some vendor doesn't use biu_clk , enable it will panic
log is below:
[  438.400868] [7:   binder:436_2: 4998] Unable to handle kernel paging request at virtual address fffffffffffffffe
[  438.400877] [7:   binder:436_2: 4998] Mem abort info:
[  438.400881] [7:   binder:436_2: 4998]   ESR = 0x0000000096000005
[  438.400887] [7:   binder:436_2: 4998]   EC = 0x25: DABT (current EL), IL = 32 bits
[  438.400894] [7:   binder:436_2: 4998]   SET = 0, FnV = 0
[  438.400899] [7:   binder:436_2: 4998]   EA = 0, S1PTW = 0
[  438.400904] [7:   binder:436_2: 4998]   FSC = 0x05: level 1 translation fault
...
[  438.409424] [7:   binder:436_2: 4998] Call trace:
[  438.409429] [7:   binder:436_2: 4998]  clk_prepare+0x10/0x24
[  438.409439] [7:   binder:436_2: 4998]  dw_mci_runtime_resume+0x50/0x2d8 [dw_mmc_samsung cd210e210975263404c28fc89778f369f8398f0c]
[  438.409471] [7:   binder:436_2: 4998]  dw_mci_exynos_runtime_resume+0x18/0x58 [dw_mmc_exynos_samsung 2735a594c7c9c9e8c65b0b87523fbf70dcaabfff]
[  438.409496] [7:   binder:436_2: 4998]  pm_generic_runtime_resume+0x40/0x58
[  438.409506] [7:   binder:436_2: 4998]  pm_runtime_force_resume+0x9c/0x134
[  438.409517] [7:   binder:436_2: 4998]  platform_pm_resume+0x40/0x8c
[  438.409529] [7:   binder:436_2: 4998]  dpm_run_callback+0x64/0x230
[  438.409540] [7:   binder:436_2: 4998]  __device_resume+0x1d8/0x394
[  438.409551] [7:   binder:436_2: 4998]  dpm_resume+0x110/0x2b8
[  438.409561] [7:   binder:436_2: 4998]  dpm_resume_end+0x1c/0x38
[  438.409570] [7:   binder:436_2: 4998]  suspend_devices_and_enter+0x828/0xab0
[  438.409582] [7:   binder:436_2: 4998]  pm_suspend+0x334/0x618
[  438.409592] [7:   binder:436_2: 4998]  state_store+0x104/0x144
[  438.409601] [7:   binder:436_2: 4998]  kobj_attr_store+0x30/0x48
[  438.409610] [7:   binder:436_2: 4998]  sysfs_kf_write+0x54/0x6c
[  438.409619] [7:   binder:436_2: 4998]  kernfs_fop_write_iter+0x104/0x1a8
[  438.409628] [7:   binder:436_2: 4998]  vfs_write+0x24c/0x2f4
[  438.409640] [7:   binder:436_2: 4998]  ksys_write+0x78/0xe8
[  438.409652] [7:   binder:436_2: 4998]  __arm64_sys_write+0x1c/0x2c
[  438.409664] [7:   binder:436_2: 4998]  invoke_syscall+0x58/0x114
[  438.409676] [7:   binder:436_2: 4998]  el0_svc_common+0xac/0xe0
[  438.409687] [7:   binder:436_2: 4998]  do_el0_svc+0x1c/0x28
[  438.409698] [7:   binder:436_2: 4998]  el0_svc+0x38/0x68
[  438.409705] [7:   binder:436_2: 4998]  el0t_64_sync_handler+0x68/0xbc
[  438.409712] [7:   binder:436_2: 4998]  el0t_64_sync+0x1a8/0x1ac
Signed-off-by: ping.gao <ping.gao@samsung.com>
---
 drivers/mmc/host/dw_mmc.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
index c5db92bbb094..61f6986f15ef 100644
--- a/drivers/mmc/host/dw_mmc.c
+++ b/drivers/mmc/host/dw_mmc.c
@@ -3633,9 +3633,15 @@ int dw_mci_runtime_resume(struct device *dev)
 	if (host->slot &&
 	    (mmc_host_can_gpio_cd(host->slot->mmc) ||
 	     !mmc_card_is_removable(host->slot->mmc))) {
-		ret = clk_prepare_enable(host->biu_clk);
-		if (ret)
-			return ret;
+		if (IS_ERR(host->biu_clk)) {
+			dev_dbg(host->dev, "biu clock not available\n");
+		} else {
+			ret = clk_prepare_enable(host->biu_clk);
+			if (ret) {
+				dev_err(host->dev, "failed to enable biu clock\n");
+				goto err;
+			}
+		}
 	}
 
 	ret = clk_prepare_enable(host->ciu_clk);
-- 
2.50.1

在 2026/01/04 星期日 10:38, ping.gao 写道:
> some vendor doesn't use biu_clk , enable it will panic
> log is below:

I still don't understand the real issue you tried to solve.

host->biu_clk is got via devm_clk_get() in dw_mci_probe(). If
succeed, immediately it's enabled a few lines below. Otherwise,
dw_mci_probe() returns with failure. Seems you are not enabling it in
runtime callbacks, but why clk_prepare_enable(host->biu_clk) is able
to work when driver probed?


> [  438.400868] [7:   binder:436_2: 4998] Unable to handle kernel paging request at virtual address fffffffffffffffe
> [  438.400877] [7:   binder:436_2: 4998] Mem abort info:
> [  438.400881] [7:   binder:436_2: 4998]   ESR = 0x0000000096000005
> [  438.400887] [7:   binder:436_2: 4998]   EC = 0x25: DABT (current EL), IL = 32 bits
> [  438.400894] [7:   binder:436_2: 4998]   SET = 0, FnV = 0
> [  438.400899] [7:   binder:436_2: 4998]   EA = 0, S1PTW = 0
> [  438.400904] [7:   binder:436_2: 4998]   FSC = 0x05: level 1 translation fault
> ...
> [  438.409424] [7:   binder:436_2: 4998] Call trace:
> [  438.409429] [7:   binder:436_2: 4998]  clk_prepare+0x10/0x24
> [  438.409439] [7:   binder:436_2: 4998]  dw_mci_runtime_resume+0x50/0x2d8 [dw_mmc_samsung cd210e210975263404c28fc89778f369f8398f0c]
> [  438.409471] [7:   binder:436_2: 4998]  dw_mci_exynos_runtime_resume+0x18/0x58 [dw_mmc_exynos_samsung 2735a594c7c9c9e8c65b0b87523fbf70dcaabfff]
> [  438.409496] [7:   binder:436_2: 4998]  pm_generic_runtime_resume+0x40/0x58
> [  438.409506] [7:   binder:436_2: 4998]  pm_runtime_force_resume+0x9c/0x134
> [  438.409517] [7:   binder:436_2: 4998]  platform_pm_resume+0x40/0x8c
> [  438.409529] [7:   binder:436_2: 4998]  dpm_run_callback+0x64/0x230
> [  438.409540] [7:   binder:436_2: 4998]  __device_resume+0x1d8/0x394
> [  438.409551] [7:   binder:436_2: 4998]  dpm_resume+0x110/0x2b8
> [  438.409561] [7:   binder:436_2: 4998]  dpm_resume_end+0x1c/0x38
> [  438.409570] [7:   binder:436_2: 4998]  suspend_devices_and_enter+0x828/0xab0
> [  438.409582] [7:   binder:436_2: 4998]  pm_suspend+0x334/0x618
> [  438.409592] [7:   binder:436_2: 4998]  state_store+0x104/0x144
> [  438.409601] [7:   binder:436_2: 4998]  kobj_attr_store+0x30/0x48
> [  438.409610] [7:   binder:436_2: 4998]  sysfs_kf_write+0x54/0x6c
> [  438.409619] [7:   binder:436_2: 4998]  kernfs_fop_write_iter+0x104/0x1a8
> [  438.409628] [7:   binder:436_2: 4998]  vfs_write+0x24c/0x2f4
> [  438.409640] [7:   binder:436_2: 4998]  ksys_write+0x78/0xe8
> [  438.409652] [7:   binder:436_2: 4998]  __arm64_sys_write+0x1c/0x2c
> [  438.409664] [7:   binder:436_2: 4998]  invoke_syscall+0x58/0x114
> [  438.409676] [7:   binder:436_2: 4998]  el0_svc_common+0xac/0xe0
> [  438.409687] [7:   binder:436_2: 4998]  do_el0_svc+0x1c/0x28
> [  438.409698] [7:   binder:436_2: 4998]  el0_svc+0x38/0x68
> [  438.409705] [7:   binder:436_2: 4998]  el0t_64_sync_handler+0x68/0xbc
> [  438.409712] [7:   binder:436_2: 4998]  el0t_64_sync+0x1a8/0x1ac
> Signed-off-by: ping.gao <ping.gao@samsung.com>
> ---
>   drivers/mmc/host/dw_mmc.c | 12 +++++++++---
>   1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
> index c5db92bbb094..61f6986f15ef 100644
> --- a/drivers/mmc/host/dw_mmc.c
> +++ b/drivers/mmc/host/dw_mmc.c
> @@ -3633,9 +3633,15 @@ int dw_mci_runtime_resume(struct device *dev)
>   	if (host->slot &&
>   	    (mmc_host_can_gpio_cd(host->slot->mmc) ||
>   	     !mmc_card_is_removable(host->slot->mmc))) {
> -		ret = clk_prepare_enable(host->biu_clk);
> -		if (ret)
> -			return ret;
> +		if (IS_ERR(host->biu_clk)) {
> +			dev_dbg(host->dev, "biu clock not available\n");
> +		} else {
> +			ret = clk_prepare_enable(host->biu_clk);
> +			if (ret) {
> +				dev_err(host->dev, "failed to enable biu clock\n");
> +				goto err;
> +			}
> +		}
>   	}
>   
>   	ret = clk_prepare_enable(host->ciu_clk);

Hi,

On Sun, Jan 04, 2026 at 10:55:48AM +0800, Shawn Lin wrote:
> 在 2026/01/04 星期日 10:38, ping.gao 写道:
> > some vendor doesn't use biu_clk , enable it will panic
> > log is below:
> 
> I still don't understand the real issue you tried to solve.
> 
> host->biu_clk is got via devm_clk_get() in dw_mci_probe(). If
> succeed, immediately it's enabled a few lines below. Otherwise,
> dw_mci_probe() returns with failure. Seems you are not enabling it in
> runtime callbacks, but why clk_prepare_enable(host->biu_clk) is able
> to work when driver probed?

Based on the error and this patch, I believe what happens is:

1. dw_mci_probe() calls devm_clk_get(host->dev, "biu")
2. The clock does not exist on the platform from Ping Gao, so
   host->biu_clk gets an error pointer assigned
3. "biu clock not available" gets printed at debug level
4. the error is ignored, but the error pointer is still assigned to
   host->biu_clk
5. in the runtime PM handler clk_prepare_enable is called for
   host->biu_clk and thus for an error pointer

Instead of hacking this up even further (as this patch does),
the proper fix is to cleanup the probe function. I believe
the complete biu clock handling in it could be reduced to this:

	host->biu_clk = devm_clk_get_optional_enabled(host->dev, "biu");
    ret = PTR_ERR_OR_ZERO(host->biu_clk);
	if (ret)
		return dev_err_probe(host->dev, ret, "failed to get biu clock\n");

That will assign NULL to host->biu_clk when there is no clock
defined and it is fine to run clk_prepare_enable() with NULL
as clock pointer. Note, that this will handle the clock enabling
as part of devm, so you will also have to drop the
clk_disable_unprepare() calls from the err_clk_biu goto label
and the extra call from dw_mci_remove().

Something similar should probably be done for host->ciu_clk, which
seems to have the same incorrect logic.

Greetings,

-- Sebastian

> > [  438.400868] [7:   binder:436_2: 4998] Unable to handle kernel paging request at virtual address fffffffffffffffe
> > [  438.400877] [7:   binder:436_2: 4998] Mem abort info:
> > [  438.400881] [7:   binder:436_2: 4998]   ESR = 0x0000000096000005
> > [  438.400887] [7:   binder:436_2: 4998]   EC = 0x25: DABT (current EL), IL = 32 bits
> > [  438.400894] [7:   binder:436_2: 4998]   SET = 0, FnV = 0
> > [  438.400899] [7:   binder:436_2: 4998]   EA = 0, S1PTW = 0
> > [  438.400904] [7:   binder:436_2: 4998]   FSC = 0x05: level 1 translation fault
> > ...
> > [  438.409424] [7:   binder:436_2: 4998] Call trace:
> > [  438.409429] [7:   binder:436_2: 4998]  clk_prepare+0x10/0x24
> > [  438.409439] [7:   binder:436_2: 4998]  dw_mci_runtime_resume+0x50/0x2d8 [dw_mmc_samsung cd210e210975263404c28fc89778f369f8398f0c]
> > [  438.409471] [7:   binder:436_2: 4998]  dw_mci_exynos_runtime_resume+0x18/0x58 [dw_mmc_exynos_samsung 2735a594c7c9c9e8c65b0b87523fbf70dcaabfff]
> > [  438.409496] [7:   binder:436_2: 4998]  pm_generic_runtime_resume+0x40/0x58
> > [  438.409506] [7:   binder:436_2: 4998]  pm_runtime_force_resume+0x9c/0x134
> > [  438.409517] [7:   binder:436_2: 4998]  platform_pm_resume+0x40/0x8c
> > [  438.409529] [7:   binder:436_2: 4998]  dpm_run_callback+0x64/0x230
> > [  438.409540] [7:   binder:436_2: 4998]  __device_resume+0x1d8/0x394
> > [  438.409551] [7:   binder:436_2: 4998]  dpm_resume+0x110/0x2b8
> > [  438.409561] [7:   binder:436_2: 4998]  dpm_resume_end+0x1c/0x38
> > [  438.409570] [7:   binder:436_2: 4998]  suspend_devices_and_enter+0x828/0xab0
> > [  438.409582] [7:   binder:436_2: 4998]  pm_suspend+0x334/0x618
> > [  438.409592] [7:   binder:436_2: 4998]  state_store+0x104/0x144
> > [  438.409601] [7:   binder:436_2: 4998]  kobj_attr_store+0x30/0x48
> > [  438.409610] [7:   binder:436_2: 4998]  sysfs_kf_write+0x54/0x6c
> > [  438.409619] [7:   binder:436_2: 4998]  kernfs_fop_write_iter+0x104/0x1a8
> > [  438.409628] [7:   binder:436_2: 4998]  vfs_write+0x24c/0x2f4
> > [  438.409640] [7:   binder:436_2: 4998]  ksys_write+0x78/0xe8
> > [  438.409652] [7:   binder:436_2: 4998]  __arm64_sys_write+0x1c/0x2c
> > [  438.409664] [7:   binder:436_2: 4998]  invoke_syscall+0x58/0x114
> > [  438.409676] [7:   binder:436_2: 4998]  el0_svc_common+0xac/0xe0
> > [  438.409687] [7:   binder:436_2: 4998]  do_el0_svc+0x1c/0x28
> > [  438.409698] [7:   binder:436_2: 4998]  el0_svc+0x38/0x68
> > [  438.409705] [7:   binder:436_2: 4998]  el0t_64_sync_handler+0x68/0xbc
> > [  438.409712] [7:   binder:436_2: 4998]  el0t_64_sync+0x1a8/0x1ac
> > Signed-off-by: ping.gao <ping.gao@samsung.com>
> > ---
> >   drivers/mmc/host/dw_mmc.c | 12 +++++++++---
> >   1 file changed, 9 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
> > index c5db92bbb094..61f6986f15ef 100644
> > --- a/drivers/mmc/host/dw_mmc.c
> > +++ b/drivers/mmc/host/dw_mmc.c
> > @@ -3633,9 +3633,15 @@ int dw_mci_runtime_resume(struct device *dev)
> >   	if (host->slot &&
> >   	    (mmc_host_can_gpio_cd(host->slot->mmc) ||
> >   	     !mmc_card_is_removable(host->slot->mmc))) {
> > -		ret = clk_prepare_enable(host->biu_clk);
> > -		if (ret)
> > -			return ret;
> > +		if (IS_ERR(host->biu_clk)) {
> > +			dev_dbg(host->dev, "biu clock not available\n");
> > +		} else {
> > +			ret = clk_prepare_enable(host->biu_clk);
> > +			if (ret) {
> > +				dev_err(host->dev, "failed to enable biu clock\n");
> > +				goto err;
> > +			}
> > +		}
> >   	}
> >   	ret = clk_prepare_enable(host->ciu_clk);
> 
> 

Hi Sevastian,

在 2026/01/04 星期日 14:01, Sebastian Reichel 写道:
> Hi,
> 
> On Sun, Jan 04, 2026 at 10:55:48AM +0800, Shawn Lin wrote:
>> 在 2026/01/04 星期日 10:38, ping.gao 写道:
>>> some vendor doesn't use biu_clk , enable it will panic
>>> log is below:
>>
>> I still don't understand the real issue you tried to solve.
>>
>> host->biu_clk is got via devm_clk_get() in dw_mci_probe(). If
>> succeed, immediately it's enabled a few lines below. Otherwise,
>> dw_mci_probe() returns with failure. Seems you are not enabling it in
>> runtime callbacks, but why clk_prepare_enable(host->biu_clk) is able
>> to work when driver probed?
> 
> Based on the error and this patch, I believe what happens is:
> 
> 1. dw_mci_probe() calls devm_clk_get(host->dev, "biu")
> 2. The clock does not exist on the platform from Ping Gao, so
>     host->biu_clk gets an error pointer assigned
> 3. "biu clock not available" gets printed at debug level
> 4. the error is ignored, but the error pointer is still assigned to
>     host->biu_clk
> 5. in the runtime PM handler clk_prepare_enable is called for
>     host->biu_clk and thus for an error pointer
> 

Thanks for the details. For example,
1. dw_mci_exynos_probe() enables runtime PM before calling
dw_mci_pltfm_register()->dw_mci_probe().
2. biu_clk gets an error and propagate it to dw_mci_pltfm_register(),
3. runtime PM is disabled in dw_mci_exynos_probe() later if seeing error.

Does that mean runtime PM handler is called between step 2 and step 3?
If that is the case, how could we allow this happen because the the
controller's configuaration isn't been finished yet. Or maybe I
misunderstand your point?


> Instead of hacking this up even further (as this patch does),
> the proper fix is to cleanup the probe function. I believe
> the complete biu clock handling in it could be reduced to this:
> 
> 	host->biu_clk = devm_clk_get_optional_enabled(host->dev, "biu");
>      ret = PTR_ERR_OR_ZERO(host->biu_clk);
> 	if (ret)
> 		return dev_err_probe(host->dev, ret, "failed to get biu clock\n");
> 
> That will assign NULL to host->biu_clk when there is no clock
> defined and it is fine to run clk_prepare_enable() with NULL
> as clock pointer. Note, that this will handle the clock enabling
> as part of devm, so you will also have to drop the
> clk_disable_unprepare() calls from the err_clk_biu goto label
> and the extra call from dw_mci_remove().
> 
> Something similar should probably be done for host->ciu_clk, which
> seems to have the same incorrect logic.
> 
> Greetings,
> 
> -- Sebastian
> 
>>> [  438.400868] [7:   binder:436_2: 4998] Unable to handle kernel paging request at virtual address fffffffffffffffe
>>> [  438.400877] [7:   binder:436_2: 4998] Mem abort info:
>>> [  438.400881] [7:   binder:436_2: 4998]   ESR = 0x0000000096000005
>>> [  438.400887] [7:   binder:436_2: 4998]   EC = 0x25: DABT (current EL), IL = 32 bits
>>> [  438.400894] [7:   binder:436_2: 4998]   SET = 0, FnV = 0
>>> [  438.400899] [7:   binder:436_2: 4998]   EA = 0, S1PTW = 0
>>> [  438.400904] [7:   binder:436_2: 4998]   FSC = 0x05: level 1 translation fault
>>> ...
>>> [  438.409424] [7:   binder:436_2: 4998] Call trace:
>>> [  438.409429] [7:   binder:436_2: 4998]  clk_prepare+0x10/0x24
>>> [  438.409439] [7:   binder:436_2: 4998]  dw_mci_runtime_resume+0x50/0x2d8 [dw_mmc_samsung cd210e210975263404c28fc89778f369f8398f0c]
>>> [  438.409471] [7:   binder:436_2: 4998]  dw_mci_exynos_runtime_resume+0x18/0x58 [dw_mmc_exynos_samsung 2735a594c7c9c9e8c65b0b87523fbf70dcaabfff]
>>> [  438.409496] [7:   binder:436_2: 4998]  pm_generic_runtime_resume+0x40/0x58
>>> [  438.409506] [7:   binder:436_2: 4998]  pm_runtime_force_resume+0x9c/0x134
>>> [  438.409517] [7:   binder:436_2: 4998]  platform_pm_resume+0x40/0x8c
>>> [  438.409529] [7:   binder:436_2: 4998]  dpm_run_callback+0x64/0x230
>>> [  438.409540] [7:   binder:436_2: 4998]  __device_resume+0x1d8/0x394
>>> [  438.409551] [7:   binder:436_2: 4998]  dpm_resume+0x110/0x2b8
>>> [  438.409561] [7:   binder:436_2: 4998]  dpm_resume_end+0x1c/0x38
>>> [  438.409570] [7:   binder:436_2: 4998]  suspend_devices_and_enter+0x828/0xab0
>>> [  438.409582] [7:   binder:436_2: 4998]  pm_suspend+0x334/0x618
>>> [  438.409592] [7:   binder:436_2: 4998]  state_store+0x104/0x144
>>> [  438.409601] [7:   binder:436_2: 4998]  kobj_attr_store+0x30/0x48
>>> [  438.409610] [7:   binder:436_2: 4998]  sysfs_kf_write+0x54/0x6c
>>> [  438.409619] [7:   binder:436_2: 4998]  kernfs_fop_write_iter+0x104/0x1a8
>>> [  438.409628] [7:   binder:436_2: 4998]  vfs_write+0x24c/0x2f4
>>> [  438.409640] [7:   binder:436_2: 4998]  ksys_write+0x78/0xe8
>>> [  438.409652] [7:   binder:436_2: 4998]  __arm64_sys_write+0x1c/0x2c
>>> [  438.409664] [7:   binder:436_2: 4998]  invoke_syscall+0x58/0x114
>>> [  438.409676] [7:   binder:436_2: 4998]  el0_svc_common+0xac/0xe0
>>> [  438.409687] [7:   binder:436_2: 4998]  do_el0_svc+0x1c/0x28
>>> [  438.409698] [7:   binder:436_2: 4998]  el0_svc+0x38/0x68
>>> [  438.409705] [7:   binder:436_2: 4998]  el0t_64_sync_handler+0x68/0xbc
>>> [  438.409712] [7:   binder:436_2: 4998]  el0t_64_sync+0x1a8/0x1ac
>>> Signed-off-by: ping.gao <ping.gao@samsung.com>
>>> ---
>>>    drivers/mmc/host/dw_mmc.c | 12 +++++++++---
>>>    1 file changed, 9 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
>>> index c5db92bbb094..61f6986f15ef 100644
>>> --- a/drivers/mmc/host/dw_mmc.c
>>> +++ b/drivers/mmc/host/dw_mmc.c
>>> @@ -3633,9 +3633,15 @@ int dw_mci_runtime_resume(struct device *dev)
>>>    	if (host->slot &&
>>>    	    (mmc_host_can_gpio_cd(host->slot->mmc) ||
>>>    	     !mmc_card_is_removable(host->slot->mmc))) {
>>> -		ret = clk_prepare_enable(host->biu_clk);
>>> -		if (ret)
>>> -			return ret;
>>> +		if (IS_ERR(host->biu_clk)) {
>>> +			dev_dbg(host->dev, "biu clock not available\n");
>>> +		} else {
>>> +			ret = clk_prepare_enable(host->biu_clk);
>>> +			if (ret) {
>>> +				dev_err(host->dev, "failed to enable biu clock\n");
>>> +				goto err;
>>> +			}
>>> +		}
>>>    	}
>>>    	ret = clk_prepare_enable(host->ciu_clk);
>>
>>

Hi,

On Sun, Jan 04, 2026 at 03:38:42PM +0800, Shawn Lin wrote:
> Hi Sevastian,
> 
> 在 2026/01/04 星期日 14:01, Sebastian Reichel 写道:
> > Hi,
> > 
> > On Sun, Jan 04, 2026 at 10:55:48AM +0800, Shawn Lin wrote:
> > > 在 2026/01/04 星期日 10:38, ping.gao 写道:
> > > > some vendor doesn't use biu_clk , enable it will panic
> > > > log is below:
> > > 
> > > I still don't understand the real issue you tried to solve.
> > > 
> > > host->biu_clk is got via devm_clk_get() in dw_mci_probe(). If
> > > succeed, immediately it's enabled a few lines below. Otherwise,
> > > dw_mci_probe() returns with failure. Seems you are not enabling it in
> > > runtime callbacks, but why clk_prepare_enable(host->biu_clk) is able
> > > to work when driver probed?
> > 
> > Based on the error and this patch, I believe what happens is:
> > 
> > 1. dw_mci_probe() calls devm_clk_get(host->dev, "biu")
> > 2. The clock does not exist on the platform from Ping Gao, so
> >     host->biu_clk gets an error pointer assigned
> > 3. "biu clock not available" gets printed at debug level
> > 4. the error is ignored, but the error pointer is still assigned to
> >     host->biu_clk
> > 5. in the runtime PM handler clk_prepare_enable is called for
> >     host->biu_clk and thus for an error pointer
> > 
> 
> Thanks for the details. For example,
> 1. dw_mci_exynos_probe() enables runtime PM before calling
> dw_mci_pltfm_register()->dw_mci_probe().
> 2. biu_clk gets an error and propagate it to dw_mci_pltfm_register(),

The error propagation does not happen. This is the current code in
dw_mci_probe():

    host->biu_clk = devm_clk_get(host->dev, "biu");
	if (IS_ERR(host->biu_clk)) {
		dev_dbg(host->dev, "biu clock not available\n");
		ret = PTR_ERR(host->biu_clk);
		if (ret == -EPROBE_DEFER)
			return ret;
        /* --- no return here --- */
	} else {
		ret = clk_prepare_enable(host->biu_clk);
		if (ret) {
			dev_err(host->dev, "failed to enable biu clock\n");
			return ret;
		}
    }

This code continues probing for any error code that is not
-EPROBE_DEFER. My understanding is, that this has been done
intensionally, since the clock does not exist on some platforms.

Effectively this is an open coded devm_clk_get_optional with
the difference that you may not use any clk_* operations on the
error code. A minimal fix would be to assign "host->biu_clk = NULL;"
at the end of the error handling code, which would open code
more of the devm_clk_get_optional() behaviour.

Obviously there is no point in having this open coded and the
helper existed since ages, so I strongly suggest to just use
that. Either devm_clk_get_optional() or even better
devm_clk_get_optional_enabled(). This results in:

 - less code, which is easier to understand
 - fixing the bug at hand
 - proper error handling for errors that are neither -EPROBE_DEFER
   nor -ENOENT.
 - better error/debug messaging behaviour for -EPROBE_DEFER when
   using dev_err_probe() instead of the dev_dbg print.

Greetings,

-- Sebastian

> 3. runtime PM is disabled in dw_mci_exynos_probe() later if seeing error.
> 
> Does that mean runtime PM handler is called between step 2 and step 3?
> If that is the case, how could we allow this happen because the the
> controller's configuaration isn't been finished yet. Or maybe I
> misunderstand your point?
> 
> 
> > Instead of hacking this up even further (as this patch does),
> > the proper fix is to cleanup the probe function. I believe
> > the complete biu clock handling in it could be reduced to this:
> > 
> > 	host->biu_clk = devm_clk_get_optional_enabled(host->dev, "biu");
> >      ret = PTR_ERR_OR_ZERO(host->biu_clk);
> > 	if (ret)
> > 		return dev_err_probe(host->dev, ret, "failed to get biu clock\n");
> > 
> > That will assign NULL to host->biu_clk when there is no clock
> > defined and it is fine to run clk_prepare_enable() with NULL
> > as clock pointer. Note, that this will handle the clock enabling
> > as part of devm, so you will also have to drop the
> > clk_disable_unprepare() calls from the err_clk_biu goto label
> > and the extra call from dw_mci_remove().
> > 
> > Something similar should probably be done for host->ciu_clk, which
> > seems to have the same incorrect logic.
> > 
> > Greetings,
> > 
> > -- Sebastian
> > 
> > > > [  438.400868] [7:   binder:436_2: 4998] Unable to handle kernel paging request at virtual address fffffffffffffffe
> > > > [  438.400877] [7:   binder:436_2: 4998] Mem abort info:
> > > > [  438.400881] [7:   binder:436_2: 4998]   ESR = 0x0000000096000005
> > > > [  438.400887] [7:   binder:436_2: 4998]   EC = 0x25: DABT (current EL), IL = 32 bits
> > > > [  438.400894] [7:   binder:436_2: 4998]   SET = 0, FnV = 0
> > > > [  438.400899] [7:   binder:436_2: 4998]   EA = 0, S1PTW = 0
> > > > [  438.400904] [7:   binder:436_2: 4998]   FSC = 0x05: level 1 translation fault
> > > > ...
> > > > [  438.409424] [7:   binder:436_2: 4998] Call trace:
> > > > [  438.409429] [7:   binder:436_2: 4998]  clk_prepare+0x10/0x24
> > > > [  438.409439] [7:   binder:436_2: 4998]  dw_mci_runtime_resume+0x50/0x2d8 [dw_mmc_samsung cd210e210975263404c28fc89778f369f8398f0c]
> > > > [  438.409471] [7:   binder:436_2: 4998]  dw_mci_exynos_runtime_resume+0x18/0x58 [dw_mmc_exynos_samsung 2735a594c7c9c9e8c65b0b87523fbf70dcaabfff]
> > > > [  438.409496] [7:   binder:436_2: 4998]  pm_generic_runtime_resume+0x40/0x58
> > > > [  438.409506] [7:   binder:436_2: 4998]  pm_runtime_force_resume+0x9c/0x134
> > > > [  438.409517] [7:   binder:436_2: 4998]  platform_pm_resume+0x40/0x8c
> > > > [  438.409529] [7:   binder:436_2: 4998]  dpm_run_callback+0x64/0x230
> > > > [  438.409540] [7:   binder:436_2: 4998]  __device_resume+0x1d8/0x394
> > > > [  438.409551] [7:   binder:436_2: 4998]  dpm_resume+0x110/0x2b8
> > > > [  438.409561] [7:   binder:436_2: 4998]  dpm_resume_end+0x1c/0x38
> > > > [  438.409570] [7:   binder:436_2: 4998]  suspend_devices_and_enter+0x828/0xab0
> > > > [  438.409582] [7:   binder:436_2: 4998]  pm_suspend+0x334/0x618
> > > > [  438.409592] [7:   binder:436_2: 4998]  state_store+0x104/0x144
> > > > [  438.409601] [7:   binder:436_2: 4998]  kobj_attr_store+0x30/0x48
> > > > [  438.409610] [7:   binder:436_2: 4998]  sysfs_kf_write+0x54/0x6c
> > > > [  438.409619] [7:   binder:436_2: 4998]  kernfs_fop_write_iter+0x104/0x1a8
> > > > [  438.409628] [7:   binder:436_2: 4998]  vfs_write+0x24c/0x2f4
> > > > [  438.409640] [7:   binder:436_2: 4998]  ksys_write+0x78/0xe8
> > > > [  438.409652] [7:   binder:436_2: 4998]  __arm64_sys_write+0x1c/0x2c
> > > > [  438.409664] [7:   binder:436_2: 4998]  invoke_syscall+0x58/0x114
> > > > [  438.409676] [7:   binder:436_2: 4998]  el0_svc_common+0xac/0xe0
> > > > [  438.409687] [7:   binder:436_2: 4998]  do_el0_svc+0x1c/0x28
> > > > [  438.409698] [7:   binder:436_2: 4998]  el0_svc+0x38/0x68
> > > > [  438.409705] [7:   binder:436_2: 4998]  el0t_64_sync_handler+0x68/0xbc
> > > > [  438.409712] [7:   binder:436_2: 4998]  el0t_64_sync+0x1a8/0x1ac
> > > > Signed-off-by: ping.gao <ping.gao@samsung.com>
> > > > ---
> > > >    drivers/mmc/host/dw_mmc.c | 12 +++++++++---
> > > >    1 file changed, 9 insertions(+), 3 deletions(-)
> > > > 
> > > > diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
> > > > index c5db92bbb094..61f6986f15ef 100644
> > > > --- a/drivers/mmc/host/dw_mmc.c
> > > > +++ b/drivers/mmc/host/dw_mmc.c
> > > > @@ -3633,9 +3633,15 @@ int dw_mci_runtime_resume(struct device *dev)
> > > >    	if (host->slot &&
> > > >    	    (mmc_host_can_gpio_cd(host->slot->mmc) ||
> > > >    	     !mmc_card_is_removable(host->slot->mmc))) {
> > > > -		ret = clk_prepare_enable(host->biu_clk);
> > > > -		if (ret)
> > > > -			return ret;
> > > > +		if (IS_ERR(host->biu_clk)) {
> > > > +			dev_dbg(host->dev, "biu clock not available\n");
> > > > +		} else {
> > > > +			ret = clk_prepare_enable(host->biu_clk);
> > > > +			if (ret) {
> > > > +				dev_err(host->dev, "failed to enable biu clock\n");
> > > > +				goto err;
> > > > +			}
> > > > +		}
> > > >    	}
> > > >    	ret = clk_prepare_enable(host->ciu_clk);
> > > 
> > > 
> 

在 2026/01/04 星期日 22:48, Sebastian Reichel 写道:
> Hi,
> 
> On Sun, Jan 04, 2026 at 03:38:42PM +0800, Shawn Lin wrote:
>> Hi Sevastian,
>>
>> 在 2026/01/04 星期日 14:01, Sebastian Reichel 写道:
>>> Hi,
>>>
>>> On Sun, Jan 04, 2026 at 10:55:48AM +0800, Shawn Lin wrote:
>>>> 在 2026/01/04 星期日 10:38, ping.gao 写道:
>>>>> some vendor doesn't use biu_clk , enable it will panic
>>>>> log is below:
>>>>
>>>> I still don't understand the real issue you tried to solve.
>>>>
>>>> host->biu_clk is got via devm_clk_get() in dw_mci_probe(). If
>>>> succeed, immediately it's enabled a few lines below. Otherwise,
>>>> dw_mci_probe() returns with failure. Seems you are not enabling it in
>>>> runtime callbacks, but why clk_prepare_enable(host->biu_clk) is able
>>>> to work when driver probed?
>>>
>>> Based on the error and this patch, I believe what happens is:
>>>
>>> 1. dw_mci_probe() calls devm_clk_get(host->dev, "biu")
>>> 2. The clock does not exist on the platform from Ping Gao, so
>>>      host->biu_clk gets an error pointer assigned
>>> 3. "biu clock not available" gets printed at debug level
>>> 4. the error is ignored, but the error pointer is still assigned to
>>>      host->biu_clk
>>> 5. in the runtime PM handler clk_prepare_enable is called for
>>>      host->biu_clk and thus for an error pointer
>>>
>>
>> Thanks for the details. For example,
>> 1. dw_mci_exynos_probe() enables runtime PM before calling
>> dw_mci_pltfm_register()->dw_mci_probe().
>> 2. biu_clk gets an error and propagate it to dw_mci_pltfm_register(),
> 
> The error propagation does not happen. This is the current code in
> dw_mci_probe():
> 
>      host->biu_clk = devm_clk_get(host->dev, "biu");
> 	if (IS_ERR(host->biu_clk)) {
> 		dev_dbg(host->dev, "biu clock not available\n");
> 		ret = PTR_ERR(host->biu_clk);
> 		if (ret == -EPROBE_DEFER)
> 			return ret;
>          /* --- no return here --- */
> 	} else {
> 		ret = clk_prepare_enable(host->biu_clk);
> 		if (ret) {
> 			dev_err(host->dev, "failed to enable biu clock\n");
> 			return ret;
> 		}
>      }
> 
> This code continues probing for any error code that is not
> -EPROBE_DEFER. My understanding is, that this has been done
> intensionally, since the clock does not exist on some platforms.
> 

I never thought of biu_clk isn't been provided as it's for accessing
register/fifo/interrupt/DMA requested by dwc databook. I was
suprised it's the optional case for some platforms. What I was thinking
is all based on that defer case.

> Effectively this is an open coded devm_clk_get_optional with
> the difference that you may not use any clk_* operations on the
> error code. A minimal fix would be to assign "host->biu_clk = NULL;"
> at the end of the error handling code, which would open code
> more of the devm_clk_get_optional() behaviour.

Yes, if it's optional case for some platforms, we should use
devm_clk_get_optional() instead, both for biu_clk and ciu_clk.
Although I will also be surprised to see ciu_clk is also
optional, the code should be consistent.

> 
> Obviously there is no point in having this open coded and the
> helper existed since ages, so I strongly suggest to just use
> that. Either devm_clk_get_optional() or even better
> devm_clk_get_optional_enabled(). This results in:
> 
>   - less code, which is easier to understand
>   - fixing the bug at hand
>   - proper error handling for errors that are neither -EPROBE_DEFER
>     nor -ENOENT.
>   - better error/debug messaging behaviour for -EPROBE_DEFER when
>     using dev_err_probe() instead of the dev_dbg print.
> 
> Greetings,
> 
> -- Sebastian
> 
>> 3. runtime PM is disabled in dw_mci_exynos_probe() later if seeing error.
>>
>> Does that mean runtime PM handler is called between step 2 and step 3?
>> If that is the case, how could we allow this happen because the the
>> controller's configuaration isn't been finished yet. Or maybe I
>> misunderstand your point?
>>
>>
>>> Instead of hacking this up even further (as this patch does),
>>> the proper fix is to cleanup the probe function. I believe
>>> the complete biu clock handling in it could be reduced to this:
>>>
>>> 	host->biu_clk = devm_clk_get_optional_enabled(host->dev, "biu");
>>>       ret = PTR_ERR_OR_ZERO(host->biu_clk);
>>> 	if (ret)
>>> 		return dev_err_probe(host->dev, ret, "failed to get biu clock\n");
>>>
>>> That will assign NULL to host->biu_clk when there is no clock
>>> defined and it is fine to run clk_prepare_enable() with NULL
>>> as clock pointer. Note, that this will handle the clock enabling
>>> as part of devm, so you will also have to drop the
>>> clk_disable_unprepare() calls from the err_clk_biu goto label
>>> and the extra call from dw_mci_remove().
>>>
>>> Something similar should probably be done for host->ciu_clk, which
>>> seems to have the same incorrect logic.
>>>
>>> Greetings,
>>>
>>> -- Sebastian
>>>
>>>>> [  438.400868] [7:   binder:436_2: 4998] Unable to handle kernel paging request at virtual address fffffffffffffffe
>>>>> [  438.400877] [7:   binder:436_2: 4998] Mem abort info:
>>>>> [  438.400881] [7:   binder:436_2: 4998]   ESR = 0x0000000096000005
>>>>> [  438.400887] [7:   binder:436_2: 4998]   EC = 0x25: DABT (current EL), IL = 32 bits
>>>>> [  438.400894] [7:   binder:436_2: 4998]   SET = 0, FnV = 0
>>>>> [  438.400899] [7:   binder:436_2: 4998]   EA = 0, S1PTW = 0
>>>>> [  438.400904] [7:   binder:436_2: 4998]   FSC = 0x05: level 1 translation fault
>>>>> ...
>>>>> [  438.409424] [7:   binder:436_2: 4998] Call trace:
>>>>> [  438.409429] [7:   binder:436_2: 4998]  clk_prepare+0x10/0x24
>>>>> [  438.409439] [7:   binder:436_2: 4998]  dw_mci_runtime_resume+0x50/0x2d8 [dw_mmc_samsung cd210e210975263404c28fc89778f369f8398f0c]
>>>>> [  438.409471] [7:   binder:436_2: 4998]  dw_mci_exynos_runtime_resume+0x18/0x58 [dw_mmc_exynos_samsung 2735a594c7c9c9e8c65b0b87523fbf70dcaabfff]
>>>>> [  438.409496] [7:   binder:436_2: 4998]  pm_generic_runtime_resume+0x40/0x58
>>>>> [  438.409506] [7:   binder:436_2: 4998]  pm_runtime_force_resume+0x9c/0x134
>>>>> [  438.409517] [7:   binder:436_2: 4998]  platform_pm_resume+0x40/0x8c
>>>>> [  438.409529] [7:   binder:436_2: 4998]  dpm_run_callback+0x64/0x230
>>>>> [  438.409540] [7:   binder:436_2: 4998]  __device_resume+0x1d8/0x394
>>>>> [  438.409551] [7:   binder:436_2: 4998]  dpm_resume+0x110/0x2b8
>>>>> [  438.409561] [7:   binder:436_2: 4998]  dpm_resume_end+0x1c/0x38
>>>>> [  438.409570] [7:   binder:436_2: 4998]  suspend_devices_and_enter+0x828/0xab0
>>>>> [  438.409582] [7:   binder:436_2: 4998]  pm_suspend+0x334/0x618
>>>>> [  438.409592] [7:   binder:436_2: 4998]  state_store+0x104/0x144
>>>>> [  438.409601] [7:   binder:436_2: 4998]  kobj_attr_store+0x30/0x48
>>>>> [  438.409610] [7:   binder:436_2: 4998]  sysfs_kf_write+0x54/0x6c
>>>>> [  438.409619] [7:   binder:436_2: 4998]  kernfs_fop_write_iter+0x104/0x1a8
>>>>> [  438.409628] [7:   binder:436_2: 4998]  vfs_write+0x24c/0x2f4
>>>>> [  438.409640] [7:   binder:436_2: 4998]  ksys_write+0x78/0xe8
>>>>> [  438.409652] [7:   binder:436_2: 4998]  __arm64_sys_write+0x1c/0x2c
>>>>> [  438.409664] [7:   binder:436_2: 4998]  invoke_syscall+0x58/0x114
>>>>> [  438.409676] [7:   binder:436_2: 4998]  el0_svc_common+0xac/0xe0
>>>>> [  438.409687] [7:   binder:436_2: 4998]  do_el0_svc+0x1c/0x28
>>>>> [  438.409698] [7:   binder:436_2: 4998]  el0_svc+0x38/0x68
>>>>> [  438.409705] [7:   binder:436_2: 4998]  el0t_64_sync_handler+0x68/0xbc
>>>>> [  438.409712] [7:   binder:436_2: 4998]  el0t_64_sync+0x1a8/0x1ac
>>>>> Signed-off-by: ping.gao <ping.gao@samsung.com>
>>>>> ---
>>>>>     drivers/mmc/host/dw_mmc.c | 12 +++++++++---
>>>>>     1 file changed, 9 insertions(+), 3 deletions(-)
>>>>>
>>>>> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
>>>>> index c5db92bbb094..61f6986f15ef 100644
>>>>> --- a/drivers/mmc/host/dw_mmc.c
>>>>> +++ b/drivers/mmc/host/dw_mmc.c
>>>>> @@ -3633,9 +3633,15 @@ int dw_mci_runtime_resume(struct device *dev)
>>>>>     	if (host->slot &&
>>>>>     	    (mmc_host_can_gpio_cd(host->slot->mmc) ||
>>>>>     	     !mmc_card_is_removable(host->slot->mmc))) {
>>>>> -		ret = clk_prepare_enable(host->biu_clk);
>>>>> -		if (ret)
>>>>> -			return ret;
>>>>> +		if (IS_ERR(host->biu_clk)) {
>>>>> +			dev_dbg(host->dev, "biu clock not available\n");
>>>>> +		} else {
>>>>> +			ret = clk_prepare_enable(host->biu_clk);
>>>>> +			if (ret) {
>>>>> +				dev_err(host->dev, "failed to enable biu clock\n");
>>>>> +				goto err;
>>>>> +			}
>>>>> +		}
>>>>>     	}
>>>>>     	ret = clk_prepare_enable(host->ciu_clk);
>>>>
>>>>
>>