Some modem devices can take significant time (up to 20 secs for sdx75) to
enter mission mode during initialization. Currently, mhi_sync_power_up()
waits for this entire process to complete, blocking other driver probes
and delaying system boot.

Switch to mhi_async_power_up() so probe can return immediately while MHI
initialization continues in the background. This eliminates lengthy boot
delays and allows other drivers to probe in parallel, improving overall
system boot performance.

Add pm_runtime_forbid() in remove path to prevent device suspend during
driver reinstallation. This issue is specific to async power up: with
sync power up, pm_runtime_put_noidle() is called after mission mode is
reached because mhi_sync_power_up() waits for mission mode event. With
async power up, pm_runtime_put_noidle() is called immediately while power
up process continues in background, which can cause the device to
suspend and mhi init fail if pm_runtime_allow() from a previous probe
is still active.

Fixes: 5571519009d0 ("bus: mhi: host: pci_generic: Add SDX75 based modem support")
Cc: stable@vger.kernel.org
Signed-off-by: Qiang Yu <qiang.yu@oss.qualcomm.com>
---
 drivers/bus/mhi/host/pci_generic.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/bus/mhi/host/pci_generic.c b/drivers/bus/mhi/host/pci_generic.c
index 0884a384b77fc3f56fa62a12351933132ffc9293..fc0952e46ae5e4854c7165ed60b850729843d458 100644
--- a/drivers/bus/mhi/host/pci_generic.c
+++ b/drivers/bus/mhi/host/pci_generic.c
@@ -1393,7 +1393,7 @@ static int mhi_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
 		goto err_unregister;
 	}
 
-	err = mhi_sync_power_up(mhi_cntrl);
+	err = mhi_async_power_up(mhi_cntrl);
 	if (err) {
 		dev_err(&pdev->dev, "failed to power up MHI controller\n");
 		goto err_unprepare;
@@ -1447,6 +1447,7 @@ static void mhi_pci_remove(struct pci_dev *pdev)
 		mhi_soc_reset(mhi_cntrl);
 
 	mhi_unregister_controller(mhi_cntrl);
+	pm_runtime_forbid(&pdev->dev);
 }
 
 static void mhi_pci_shutdown(struct pci_dev *pdev)

---
base-commit: 91a0b0dce350766675961892ba4431363c4e29f7
change-id: 20260113-mhi_async_probe-a7b0867b6e2e

Best regards,
-- 
Qiang Yu <qiang.yu@oss.qualcomm.com>

On Thu, Jan 22, 2026 at 12:53:48AM -0800, Qiang Yu wrote:
> Some modem devices can take significant time (up to 20 secs for sdx75) to
> enter mission mode during initialization. Currently, mhi_sync_power_up()
> waits for this entire process to complete, blocking other driver probes
> and delaying system boot.
> 
> Switch to mhi_async_power_up() so probe can return immediately while MHI
> initialization continues in the background. This eliminates lengthy boot
> delays and allows other drivers to probe in parallel, improving overall
> system boot performance.
> 

This part is fine.

> Add pm_runtime_forbid() in remove path to prevent device suspend during
> driver reinstallation. This issue is specific to async power up: with
> sync power up, pm_runtime_put_noidle() is called after mission mode is
> reached because mhi_sync_power_up() waits for mission mode event. With
> async power up, pm_runtime_put_noidle() is called immediately while power
> up process continues in background, which can cause the device to
> suspend and mhi init fail if pm_runtime_allow() from a previous probe
> is still active.
> 

pm_runtime_forbid() should be called at the start of the remove() callback to
prevent the device from auto suspending during cleanup and to fix the issue you
described above.

So do in a separate patch and add a Fixes tag pointing to the commit that added
the Runtime PM support.

- Mani

> Fixes: 5571519009d0 ("bus: mhi: host: pci_generic: Add SDX75 based modem support")
> Cc: stable@vger.kernel.org
> Signed-off-by: Qiang Yu <qiang.yu@oss.qualcomm.com>
> ---
>  drivers/bus/mhi/host/pci_generic.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/bus/mhi/host/pci_generic.c b/drivers/bus/mhi/host/pci_generic.c
> index 0884a384b77fc3f56fa62a12351933132ffc9293..fc0952e46ae5e4854c7165ed60b850729843d458 100644
> --- a/drivers/bus/mhi/host/pci_generic.c
> +++ b/drivers/bus/mhi/host/pci_generic.c
> @@ -1393,7 +1393,7 @@ static int mhi_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
>  		goto err_unregister;
>  	}
>  
> -	err = mhi_sync_power_up(mhi_cntrl);
> +	err = mhi_async_power_up(mhi_cntrl);
>  	if (err) {
>  		dev_err(&pdev->dev, "failed to power up MHI controller\n");
>  		goto err_unprepare;
> @@ -1447,6 +1447,7 @@ static void mhi_pci_remove(struct pci_dev *pdev)
>  		mhi_soc_reset(mhi_cntrl);
>  
>  	mhi_unregister_controller(mhi_cntrl);
> +	pm_runtime_forbid(&pdev->dev);
>  }
>  
>  static void mhi_pci_shutdown(struct pci_dev *pdev)
> 
> ---
> base-commit: 91a0b0dce350766675961892ba4431363c4e29f7
> change-id: 20260113-mhi_async_probe-a7b0867b6e2e
> 
> Best regards,
> -- 
> Qiang Yu <qiang.yu@oss.qualcomm.com>
> 

-- 
மணிவண்ணன் சதாசிவம்

On Mon, Mar 02, 2026 at 01:37:38PM +0530, Manivannan Sadhasivam wrote:
> On Thu, Jan 22, 2026 at 12:53:48AM -0800, Qiang Yu wrote:
> > Some modem devices can take significant time (up to 20 secs for sdx75) to
> > enter mission mode during initialization. Currently, mhi_sync_power_up()
> > waits for this entire process to complete, blocking other driver probes
> > and delaying system boot.
> > 
> > Switch to mhi_async_power_up() so probe can return immediately while MHI
> > initialization continues in the background. This eliminates lengthy boot
> > delays and allows other drivers to probe in parallel, improving overall
> > system boot performance.
> > 
> 
> This part is fine.
> 
> > Add pm_runtime_forbid() in remove path to prevent device suspend during
> > driver reinstallation. This issue is specific to async power up: with
> > sync power up, pm_runtime_put_noidle() is called after mission mode is
> > reached because mhi_sync_power_up() waits for mission mode event. With
> > async power up, pm_runtime_put_noidle() is called immediately while power
> > up process continues in background, which can cause the device to
> > suspend and mhi init fail if pm_runtime_allow() from a previous probe
> > is still active.
> > 
> 
> pm_runtime_forbid() should be called at the start of the remove() callback to
> prevent the device from auto suspending during cleanup and to fix the issue you
> described above.
> 
> So do in a separate patch and add a Fixes tag pointing to the commit that added
> the Runtime PM support.
>

I can implement this in a separate patch as it also serves as a cleanup to
call pm_runtime_forbid() in the remove callback, since we call
pm_runtime_allow() in our driver. However, I cannot call it at the start
of the remove() callback. Before the remove callback is invoked,
pci_device_remove() calls pm_runtime_get_sync(dev) first, so we don't need
to worry about auto-suspend during removal.

Since we use mhi_async_power_up(), there's a race condition where the
mhi_pci_generic driver could be removed after mission mode is reached but
before pm_runtime_allow() is called as part of mhi_status_cb(). In this
scenario, the pm_runtime_forbid() operation would be ineffective, and when
the driver is reinstalled next time, MHI read operations will fail during
initialization because the previous pm_runtime_allow() state was not
properly cleared.

- Qiang Yu
> - Mani
> 
> > Fixes: 5571519009d0 ("bus: mhi: host: pci_generic: Add SDX75 based modem support")
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Qiang Yu <qiang.yu@oss.qualcomm.com>
> > ---
> >  drivers/bus/mhi/host/pci_generic.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/bus/mhi/host/pci_generic.c b/drivers/bus/mhi/host/pci_generic.c
> > index 0884a384b77fc3f56fa62a12351933132ffc9293..fc0952e46ae5e4854c7165ed60b850729843d458 100644
> > --- a/drivers/bus/mhi/host/pci_generic.c
> > +++ b/drivers/bus/mhi/host/pci_generic.c
> > @@ -1393,7 +1393,7 @@ static int mhi_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
> >  		goto err_unregister;
> >  	}
> >  
> > -	err = mhi_sync_power_up(mhi_cntrl);
> > +	err = mhi_async_power_up(mhi_cntrl);
> >  	if (err) {
> >  		dev_err(&pdev->dev, "failed to power up MHI controller\n");
> >  		goto err_unprepare;
> > @@ -1447,6 +1447,7 @@ static void mhi_pci_remove(struct pci_dev *pdev)
> >  		mhi_soc_reset(mhi_cntrl);
> >  
> >  	mhi_unregister_controller(mhi_cntrl);
> > +	pm_runtime_forbid(&pdev->dev);
> >  }
> >  
> >  static void mhi_pci_shutdown(struct pci_dev *pdev)
> > 
> > ---
> > base-commit: 91a0b0dce350766675961892ba4431363c4e29f7
> > change-id: 20260113-mhi_async_probe-a7b0867b6e2e
> > 
> > Best regards,
> > -- 
> > Qiang Yu <qiang.yu@oss.qualcomm.com>
> > 
> 
> -- 
> மணிவண்ணன் சதாசிவம்

On Mon, Mar 02, 2026 at 02:06:56AM -0800, Qiang Yu wrote:
> On Mon, Mar 02, 2026 at 01:37:38PM +0530, Manivannan Sadhasivam wrote:
> > On Thu, Jan 22, 2026 at 12:53:48AM -0800, Qiang Yu wrote:
> > > Some modem devices can take significant time (up to 20 secs for sdx75) to
> > > enter mission mode during initialization. Currently, mhi_sync_power_up()
> > > waits for this entire process to complete, blocking other driver probes
> > > and delaying system boot.
> > > 
> > > Switch to mhi_async_power_up() so probe can return immediately while MHI
> > > initialization continues in the background. This eliminates lengthy boot
> > > delays and allows other drivers to probe in parallel, improving overall
> > > system boot performance.
> > > 
> > 
> > This part is fine.
> > 
> > > Add pm_runtime_forbid() in remove path to prevent device suspend during
> > > driver reinstallation. This issue is specific to async power up: with
> > > sync power up, pm_runtime_put_noidle() is called after mission mode is
> > > reached because mhi_sync_power_up() waits for mission mode event. With
> > > async power up, pm_runtime_put_noidle() is called immediately while power
> > > up process continues in background, which can cause the device to
> > > suspend and mhi init fail if pm_runtime_allow() from a previous probe
> > > is still active.
> > > 
> > 
> > pm_runtime_forbid() should be called at the start of the remove() callback to
> > prevent the device from auto suspending during cleanup and to fix the issue you
> > described above.
> > 
> > So do in a separate patch and add a Fixes tag pointing to the commit that added
> > the Runtime PM support.
> >
> 
> I can implement this in a separate patch as it also serves as a cleanup to
> call pm_runtime_forbid() in the remove callback, since we call
> pm_runtime_allow() in our driver. However, I cannot call it at the start
> of the remove() callback. Before the remove callback is invoked,
> pci_device_remove() calls pm_runtime_get_sync(dev) first, so we don't need
> to worry about auto-suspend during removal.
> 

Three issues here:

1. remove() callback uses pm_runtime_get_noresume(), which wouldn't guarantee
that the driver will be resumed (if suspended) during remove operation. So there
is a good chance that the device access will fail.

2. Moreover, pm_runtime_get_noresume() is called at the end of the remove()
callback, which is also too late.

3. Even if the above two gets fixed, we should make sure that the autosuspend
should be stopped before executing remove() as the autosuspend timer will start
and expire in parallel. This is not causing any issue as of now, but it would be
canolical to fix it.

I've submitted a fix for the first two issues:
https://lore.kernel.org/mhi/20260302134116.18960-1-manivannan.sadhasivam@oss.qualcomm.com

You should fix the third one in a separate patch in this series. Hope this
clarifies!

- Mani

-- 
மணிவண்ணன் சதாசிவம்