iTCO_wdt: ignore NMI_NOW bit on register comparison

[PATCH v1] iTCO_wdt: ignore NMI_NOW bit on register comparison

Posted by Oleksandr Ocheretnyi 1 year, 3 months ago

Commit da23b6faa8bf ("watchdog: iTCO: Add support for Cannon Lake
PCH iTCO") does not ignore NMI_NOW bit on write operation to TCO1_CNT
register what causes unexpected NMIs due to NMI_NOW bit inversion
during regular crashkernel's workflow with following logs:

iTCO_vendor_support: vendor-support=0
iTCO_wdt iTCO_wdt: unable to reset NO_REBOOT flag, device
                                            disabled by hardware/BIOS

This change clears NMI_NOW bit in the TCO1_CNT register to have no
effect on NMI_NOW bit inversion what can cause NMI immediately.

Fixes: da23b6faa8bf ("watchdog: iTCO: Add support for Cannon Lake PCH iTCO")
Signed-off-by: Oleksandr Ocheretnyi <oocheret@cisco.com>
---
 drivers/watchdog/iTCO_wdt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/watchdog/iTCO_wdt.c b/drivers/watchdog/iTCO_wdt.c
index 264857d314da..679c115ef7d3 100644
--- a/drivers/watchdog/iTCO_wdt.c
+++ b/drivers/watchdog/iTCO_wdt.c
@@ -224,7 +224,7 @@ static int update_no_reboot_bit_cnt(void *priv, bool set)
 		val |= BIT(0);
 	else
 		val &= ~BIT(0);
-	outw(val, TCO1_CNT(p));
+	outw(val & ~BIT(8), TCO1_CNT(p));
 	newval = inw(TCO1_CNT(p));
 
 	/* make sure the update is successful */
-- 
2.39.3

Re: [PATCH v1] iTCO_wdt: ignore NMI_NOW bit on register comparison

Posted by Mika Westerberg 1 year, 3 months ago

Hi,

On Mon, Aug 26, 2024 at 12:53:01AM -0700, Oleksandr Ocheretnyi wrote:
> Commit da23b6faa8bf ("watchdog: iTCO: Add support for Cannon Lake
> PCH iTCO") does not ignore NMI_NOW bit on write operation to TCO1_CNT
> register what causes unexpected NMIs due to NMI_NOW bit inversion
> during regular crashkernel's workflow with following logs:
> 
> iTCO_vendor_support: vendor-support=0
> iTCO_wdt iTCO_wdt: unable to reset NO_REBOOT flag, device
>                                             disabled by hardware/BIOS
> 
> This change clears NMI_NOW bit in the TCO1_CNT register to have no
> effect on NMI_NOW bit inversion what can cause NMI immediately.
> 
> Fixes: da23b6faa8bf ("watchdog: iTCO: Add support for Cannon Lake PCH iTCO")
> Signed-off-by: Oleksandr Ocheretnyi <oocheret@cisco.com>
> ---
>  drivers/watchdog/iTCO_wdt.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/watchdog/iTCO_wdt.c b/drivers/watchdog/iTCO_wdt.c
> index 264857d314da..679c115ef7d3 100644
> --- a/drivers/watchdog/iTCO_wdt.c
> +++ b/drivers/watchdog/iTCO_wdt.c
> @@ -224,7 +224,7 @@ static int update_no_reboot_bit_cnt(void *priv, bool set)
>  		val |= BIT(0);
>  	else
>  		val &= ~BIT(0);
> -	outw(val, TCO1_CNT(p));
> +	outw(val & ~BIT(8), TCO1_CNT(p));

I suggest adding some #define for the magical number 8 so that it is
easier for anyone looking at this driver to figure out what it is doing.

Otherwise looks good to me, thanks!

>  	newval = inw(TCO1_CNT(p));
>  
>  	/* make sure the update is successful */
> -- 
> 2.39.3

Re: [PATCH v1] iTCO_wdt: ignore NMI_NOW bit on register comparison

Posted by Guenter Roeck 1 year, 3 months ago

On 8/26/24 04:18, Mika Westerberg wrote:
> Hi,
> 
> On Mon, Aug 26, 2024 at 12:53:01AM -0700, Oleksandr Ocheretnyi wrote:
>> Commit da23b6faa8bf ("watchdog: iTCO: Add support for Cannon Lake
>> PCH iTCO") does not ignore NMI_NOW bit on write operation to TCO1_CNT
>> register what causes unexpected NMIs due to NMI_NOW bit inversion
>> during regular crashkernel's workflow with following logs:
>>
>> iTCO_vendor_support: vendor-support=0
>> iTCO_wdt iTCO_wdt: unable to reset NO_REBOOT flag, device
>>                                              disabled by hardware/BIOS
>>
>> This change clears NMI_NOW bit in the TCO1_CNT register to have no
>> effect on NMI_NOW bit inversion what can cause NMI immediately.
>>
>> Fixes: da23b6faa8bf ("watchdog: iTCO: Add support for Cannon Lake PCH iTCO")
>> Signed-off-by: Oleksandr Ocheretnyi <oocheret@cisco.com>
>> ---
>>   drivers/watchdog/iTCO_wdt.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/watchdog/iTCO_wdt.c b/drivers/watchdog/iTCO_wdt.c
>> index 264857d314da..679c115ef7d3 100644
>> --- a/drivers/watchdog/iTCO_wdt.c
>> +++ b/drivers/watchdog/iTCO_wdt.c
>> @@ -224,7 +224,7 @@ static int update_no_reboot_bit_cnt(void *priv, bool set)
>>   		val |= BIT(0);
>>   	else
>>   		val &= ~BIT(0);
>> -	outw(val, TCO1_CNT(p));
>> +	outw(val & ~BIT(8), TCO1_CNT(p));
> 
> I suggest adding some #define for the magical number 8 so that it is
> easier for anyone looking at this driver to figure out what it is doing.
> 
> Otherwise looks good to me, thanks!
> 

Not really; it appears to be hiding a change in code which is supposed to do
something different (it is supposed to set or clear the no_reboot bit),
with no explanation whatsoever. That warrants a comment in the code.
Also, I would prefer
	val = inw(TCO1_CNT(p)) & ~BIT(8);

Guenter

>>   	newval = inw(TCO1_CNT(p));
>>   
>>   	/* make sure the update is successful */
>> -- 
>> 2.39.3

Re: [PATCH v1] iTCO_wdt: ignore NMI_NOW bit on register comparison

Posted by Guenter Roeck 1 year, 3 months ago

On 8/26/24 08:12, Guenter Roeck wrote:
> On 8/26/24 04:18, Mika Westerberg wrote:
>> Hi,
>>
>> On Mon, Aug 26, 2024 at 12:53:01AM -0700, Oleksandr Ocheretnyi wrote:
>>> Commit da23b6faa8bf ("watchdog: iTCO: Add support for Cannon Lake
>>> PCH iTCO") does not ignore NMI_NOW bit on write operation to TCO1_CNT
>>> register what causes unexpected NMIs due to NMI_NOW bit inversion
>>> during regular crashkernel's workflow with following logs:
>>>
>>> iTCO_vendor_support: vendor-support=0
>>> iTCO_wdt iTCO_wdt: unable to reset NO_REBOOT flag, device
>>>                                              disabled by hardware/BIOS
>>>
>>> This change clears NMI_NOW bit in the TCO1_CNT register to have no
>>> effect on NMI_NOW bit inversion what can cause NMI immediately.
>>>
>>> Fixes: da23b6faa8bf ("watchdog: iTCO: Add support for Cannon Lake PCH iTCO")
>>> Signed-off-by: Oleksandr Ocheretnyi <oocheret@cisco.com>
>>> ---
>>>   drivers/watchdog/iTCO_wdt.c | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/watchdog/iTCO_wdt.c b/drivers/watchdog/iTCO_wdt.c
>>> index 264857d314da..679c115ef7d3 100644
>>> --- a/drivers/watchdog/iTCO_wdt.c
>>> +++ b/drivers/watchdog/iTCO_wdt.c
>>> @@ -224,7 +224,7 @@ static int update_no_reboot_bit_cnt(void *priv, bool set)
>>>           val |= BIT(0);
>>>       else
>>>           val &= ~BIT(0);
>>> -    outw(val, TCO1_CNT(p));
>>> +    outw(val & ~BIT(8), TCO1_CNT(p));
>>
>> I suggest adding some #define for the magical number 8 so that it is
>> easier for anyone looking at this driver to figure out what it is doing.
>>
>> Otherwise looks good to me, thanks!
>>
> 
> Not really; it appears to be hiding a change in code which is supposed to do
> something different (it is supposed to set or clear the no_reboot bit),
> with no explanation whatsoever. That warrants a comment in the code.
> Also, I would prefer
>      val = inw(TCO1_CNT(p)) & ~BIT(8);
> 

On top of that, I fail to understand "on register comparison" in the subject.
What register comparison ?

Guenter

Re: [PATCH v1] iTCO_wdt: ignore NMI_NOW bit on register comparison

Posted by Guenter Roeck 1 year, 3 months ago

On 8/26/24 08:15, Guenter Roeck wrote:
> On 8/26/24 08:12, Guenter Roeck wrote:
>> On 8/26/24 04:18, Mika Westerberg wrote:
>>> Hi,
>>>
>>> On Mon, Aug 26, 2024 at 12:53:01AM -0700, Oleksandr Ocheretnyi wrote:
>>>> Commit da23b6faa8bf ("watchdog: iTCO: Add support for Cannon Lake
>>>> PCH iTCO") does not ignore NMI_NOW bit on write operation to TCO1_CNT
>>>> register what causes unexpected NMIs due to NMI_NOW bit inversion
>>>> during regular crashkernel's workflow with following logs:
>>>>
>>>> iTCO_vendor_support: vendor-support=0
>>>> iTCO_wdt iTCO_wdt: unable to reset NO_REBOOT flag, device
>>>>                                              disabled by hardware/BIOS
>>>>
>>>> This change clears NMI_NOW bit in the TCO1_CNT register to have no
>>>> effect on NMI_NOW bit inversion what can cause NMI immediately.
>>>>
>>>> Fixes: da23b6faa8bf ("watchdog: iTCO: Add support for Cannon Lake PCH iTCO")
>>>> Signed-off-by: Oleksandr Ocheretnyi <oocheret@cisco.com>
>>>> ---
>>>>   drivers/watchdog/iTCO_wdt.c | 2 +-
>>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/watchdog/iTCO_wdt.c b/drivers/watchdog/iTCO_wdt.c
>>>> index 264857d314da..679c115ef7d3 100644
>>>> --- a/drivers/watchdog/iTCO_wdt.c
>>>> +++ b/drivers/watchdog/iTCO_wdt.c
>>>> @@ -224,7 +224,7 @@ static int update_no_reboot_bit_cnt(void *priv, bool set)
>>>>           val |= BIT(0);
>>>>       else
>>>>           val &= ~BIT(0);
>>>> -    outw(val, TCO1_CNT(p));
>>>> +    outw(val & ~BIT(8), TCO1_CNT(p));
>>>
>>> I suggest adding some #define for the magical number 8 so that it is
>>> easier for anyone looking at this driver to figure out what it is doing.
>>>
>>> Otherwise looks good to me, thanks!
>>>
>>
>> Not really; it appears to be hiding a change in code which is supposed to do
>> something different (it is supposed to set or clear the no_reboot bit),
>> with no explanation whatsoever. That warrants a comment in the code.
>> Also, I would prefer
>>      val = inw(TCO1_CNT(p)) & ~BIT(8);
>>
> 
> On top of that, I fail to understand "on register comparison" in the subject.
> What register comparison ?
> 

Sorry, one more: The comment will need to explain why clearing bit 8 is needed
here but not for any other writes to TCO1_CNT. Obviously this isn't just "ignore
bit on write" but something more.

Guenter

[PATCH v2] iTCO_wdt: mask NMI_NOW bit for update_no_reboot_bit() call

Posted by Oleksandr Ocheretnyi 1 year, 3 months ago

Commit da23b6faa8bf ("watchdog: iTCO: Add support for Cannon Lake
PCH iTCO") does not mask NMI_NOW bit during TCO1_CNT register's
value comparison for update_no_reboot_bit() call causing following
failure:

   ...
   iTCO_vendor_support: vendor-support=0
   iTCO_wdt iTCO_wdt: unable to reset NO_REBOOT flag, device
                                    disabled by hardware/BIOS
   ...

and this can lead to unexpected NMIs later during regular
crashkernel's workflow because of watchdog probe call failures.

This change masks NMI_NOW bit for TCO1_CNT register values to
avoid unexpected NMI_NOW bit inversions.

Fixes: da23b6faa8bf ("watchdog: iTCO: Add support for Cannon Lake PCH iTCO")
Signed-off-by: Oleksandr Ocheretnyi <oocheret@cisco.com>
---
 drivers/watchdog/iTCO_wdt.c | 23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/drivers/watchdog/iTCO_wdt.c b/drivers/watchdog/iTCO_wdt.c
index 264857d314da..46c09359588f 100644
--- a/drivers/watchdog/iTCO_wdt.c
+++ b/drivers/watchdog/iTCO_wdt.c
@@ -82,6 +82,12 @@
 #define TCO2_CNT(p)	(TCOBASE(p) + 0x0a) /* TCO2 Control Register	*/
 #define TCOv2_TMR(p)	(TCOBASE(p) + 0x12) /* TCOv2 Timer Initial Value*/
 
+/* NMI_NOW is bit 8 of TCO1_CNT register
+ * Read/Write
+ * This bit is implemented as RW but has no effect on HW.
+ */
+#define NMI_NOW		BIT(8)
+
 /* internal variables */
 struct iTCO_wdt_private {
 	struct watchdog_device wddev;
@@ -217,15 +223,24 @@ static int update_no_reboot_bit_mem(void *priv, bool set)
 static int update_no_reboot_bit_cnt(void *priv, bool set)
 {
 	struct iTCO_wdt_private *p = priv;
-	u16 val, newval;
-
-	val = inw(TCO1_CNT(p));
+	u16 val, newval, mask = (~NMI_NOW);
+
+	/* writing back 1b1 to NMI_NOW of TCO1_CNT register
+	 * causes NMI_NOW bit inversion what consequently does
+	 * not allow to perform the register's value comparison
+	 * properly.
+	 *
+	 * NMI_NOW bit masking for TCO1_CNT register values
+	 * helps to avoid possible NMI_NOW bit inversions on
+	 * following write operation.
+	 */
+	val = inw(TCO1_CNT(p)) & mask;
 	if (set)
 		val |= BIT(0);
 	else
 		val &= ~BIT(0);
 	outw(val, TCO1_CNT(p));
-	newval = inw(TCO1_CNT(p));
+	newval = inw(TCO1_CNT(p)) & mask;
 
 	/* make sure the update is successful */
 	return val != newval ? -EIO : 0;
-- 
2.35.6

Re: [PATCH v2] iTCO_wdt: mask NMI_NOW bit for update_no_reboot_bit() call

Posted by kernel test robot 1 year, 3 months ago

Hi Oleksandr,

kernel test robot noticed the following build warnings:

[auto build test WARNING on westeri-thunderbolt/next]
[also build test WARNING on linus/master v6.11-rc7 next-20240912]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Oleksandr-Ocheretnyi/iTCO_wdt-mask-NMI_NOW-bit-for-update_no_reboot_bit-call/20240912-222231
base:   https://git.kernel.org/pub/scm/linux/kernel/git/westeri/thunderbolt.git next
patch link:    https://lore.kernel.org/r/20240912141931.2447826-1-oocheret%40cisco.com
patch subject: [PATCH v2] iTCO_wdt: mask NMI_NOW bit for update_no_reboot_bit() call
config: i386-buildonly-randconfig-001-20240913 (https://download.01.org/0day-ci/archive/20240913/202409131548.X0MGdN1r-lkp@intel.com/config)
compiler: clang version 18.1.8 (https://github.com/llvm/llvm-project 3b5b5c1ec4a3095ab096dd780e84d7ab81f3d7ff)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240913/202409131548.X0MGdN1r-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202409131548.X0MGdN1r-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> drivers/watchdog/iTCO_wdt.c:226:27: warning: implicit conversion from 'unsigned long' to 'u16' (aka 'unsigned short') changes value from 4294967039 to 65279 [-Wconstant-conversion]
     226 |         u16 val, newval, mask = (~NMI_NOW);
         |                          ~~~~    ^~~~~~~~
   1 warning generated.


vim +226 drivers/watchdog/iTCO_wdt.c

   222	
   223	static int update_no_reboot_bit_cnt(void *priv, bool set)
   224	{
   225		struct iTCO_wdt_private *p = priv;
 > 226		u16 val, newval, mask = (~NMI_NOW);
   227	
   228		/* writing back 1b1 to NMI_NOW of TCO1_CNT register
   229		 * causes NMI_NOW bit inversion what consequently does
   230		 * not allow to perform the register's value comparison
   231		 * properly.
   232		 *
   233		 * NMI_NOW bit masking for TCO1_CNT register values
   234		 * helps to avoid possible NMI_NOW bit inversions on
   235		 * following write operation.
   236		 */
   237		val = inw(TCO1_CNT(p)) & mask;
   238		if (set)
   239			val |= BIT(0);
   240		else
   241			val &= ~BIT(0);
   242		outw(val, TCO1_CNT(p));
   243		newval = inw(TCO1_CNT(p)) & mask;
   244	
   245		/* make sure the update is successful */
   246		return val != newval ? -EIO : 0;
   247	}
   248	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH v2] iTCO_wdt: mask NMI_NOW bit for update_no_reboot_bit() call

Posted by kernel test robot 1 year, 3 months ago

Hi Oleksandr,

kernel test robot noticed the following build warnings:

[auto build test WARNING on westeri-thunderbolt/next]
[also build test WARNING on linus/master v6.11-rc7 next-20240912]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Oleksandr-Ocheretnyi/iTCO_wdt-mask-NMI_NOW-bit-for-update_no_reboot_bit-call/20240912-222231
base:   https://git.kernel.org/pub/scm/linux/kernel/git/westeri/thunderbolt.git next
patch link:    https://lore.kernel.org/r/20240912141931.2447826-1-oocheret%40cisco.com
patch subject: [PATCH v2] iTCO_wdt: mask NMI_NOW bit for update_no_reboot_bit() call
config: i386-buildonly-randconfig-003-20240913 (https://download.01.org/0day-ci/archive/20240913/202409131302.oGABipcM-lkp@intel.com/config)
compiler: gcc-12 (Debian 12.2.0-14) 12.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240913/202409131302.oGABipcM-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202409131302.oGABipcM-lkp@intel.com/

All warnings (new ones prefixed by >>):

   drivers/watchdog/iTCO_wdt.c: In function 'update_no_reboot_bit_cnt':
>> drivers/watchdog/iTCO_wdt.c:226:33: warning: conversion from 'long unsigned int' to 'u16' {aka 'short unsigned int'} changes value from '4294967039' to '65279' [-Woverflow]
     226 |         u16 val, newval, mask = (~NMI_NOW);
         |                                 ^


vim +226 drivers/watchdog/iTCO_wdt.c

   222	
   223	static int update_no_reboot_bit_cnt(void *priv, bool set)
   224	{
   225		struct iTCO_wdt_private *p = priv;
 > 226		u16 val, newval, mask = (~NMI_NOW);
   227	
   228		/* writing back 1b1 to NMI_NOW of TCO1_CNT register
   229		 * causes NMI_NOW bit inversion what consequently does
   230		 * not allow to perform the register's value comparison
   231		 * properly.
   232		 *
   233		 * NMI_NOW bit masking for TCO1_CNT register values
   234		 * helps to avoid possible NMI_NOW bit inversions on
   235		 * following write operation.
   236		 */
   237		val = inw(TCO1_CNT(p)) & mask;
   238		if (set)
   239			val |= BIT(0);
   240		else
   241			val &= ~BIT(0);
   242		outw(val, TCO1_CNT(p));
   243		newval = inw(TCO1_CNT(p)) & mask;
   244	
   245		/* make sure the update is successful */
   246		return val != newval ? -EIO : 0;
   247	}
   248	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH v2] iTCO_wdt: mask NMI_NOW bit for update_no_reboot_bit() call

Posted by Guenter Roeck 1 year, 3 months ago

On 9/12/24 07:19, Oleksandr Ocheretnyi wrote:
> Commit da23b6faa8bf ("watchdog: iTCO: Add support for Cannon Lake
> PCH iTCO") does not mask NMI_NOW bit during TCO1_CNT register's
> value comparison for update_no_reboot_bit() call causing following
> failure:
> 
>     ...
>     iTCO_vendor_support: vendor-support=0
>     iTCO_wdt iTCO_wdt: unable to reset NO_REBOOT flag, device
>                                      disabled by hardware/BIOS
>     ...
> 
> and this can lead to unexpected NMIs later during regular
> crashkernel's workflow because of watchdog probe call failures.
> 
> This change masks NMI_NOW bit for TCO1_CNT register values to
> avoid unexpected NMI_NOW bit inversions.
> 
> Fixes: da23b6faa8bf ("watchdog: iTCO: Add support for Cannon Lake PCH iTCO")
> Signed-off-by: Oleksandr Ocheretnyi <oocheret@cisco.com>
> ---

Oh, and change log goes here.

Guenter

[PATCH v3] iTCO_wdt: mask NMI_NOW bit for update_no_reboot_bit() call

Posted by Oleksandr Ocheretnyi 1 year, 3 months ago

Commit da23b6faa8bf ("watchdog: iTCO: Add support for Cannon Lake
PCH iTCO") does not mask NMI_NOW bit during TCO1_CNT register's
value comparison for update_no_reboot_bit() call causing following
failure:

   ...
   iTCO_vendor_support: vendor-support=0
   iTCO_wdt iTCO_wdt: unable to reset NO_REBOOT flag, device
                                    disabled by hardware/BIOS
   ...

and this can lead to unexpected NMIs later during regular
crashkernel's workflow because of watchdog probe call failures.

This change masks NMI_NOW bit for TCO1_CNT register values to
avoid unexpected NMI_NOW bit inversions.

Fixes: da23b6faa8bf ("watchdog: iTCO: Add support for Cannon Lake PCH iTCO")
Signed-off-by: Oleksandr Ocheretnyi <oocheret@cisco.com>
---
 V2 -> V3: Removed not necessary variable 'mask', updated multi-line comments
 V1 -> V2: Provided comments and macro define with bit description

 drivers/watchdog/iTCO_wdt.c | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/drivers/watchdog/iTCO_wdt.c b/drivers/watchdog/iTCO_wdt.c
index 264857d314da..dd297dcd524c 100644
--- a/drivers/watchdog/iTCO_wdt.c
+++ b/drivers/watchdog/iTCO_wdt.c
@@ -82,6 +82,13 @@
 #define TCO2_CNT(p)	(TCOBASE(p) + 0x0a) /* TCO2 Control Register	*/
 #define TCOv2_TMR(p)	(TCOBASE(p) + 0x12) /* TCOv2 Timer Initial Value*/
 
+/*
+ * NMI_NOW is bit 8 of TCO1_CNT register
+ * Read/Write
+ * This bit is implemented as RW but has no effect on HW.
+ */
+#define NMI_NOW		BIT(8)
+
 /* internal variables */
 struct iTCO_wdt_private {
 	struct watchdog_device wddev;
@@ -219,13 +226,23 @@ static int update_no_reboot_bit_cnt(void *priv, bool set)
 	struct iTCO_wdt_private *p = priv;
 	u16 val, newval;
 
-	val = inw(TCO1_CNT(p));
+	/*
+	 * writing back 1b1 to NMI_NOW of TCO1_CNT register
+	 * causes NMI_NOW bit inversion what consequently does
+	 * not allow to perform the register's value comparison
+	 * properly.
+	 *
+	 * NMI_NOW bit masking for TCO1_CNT register values
+	 * helps to avoid possible NMI_NOW bit inversions on
+	 * following write operation.
+	 */
+	val = inw(TCO1_CNT(p)) & ~NMI_NOW;
 	if (set)
 		val |= BIT(0);
 	else
 		val &= ~BIT(0);
 	outw(val, TCO1_CNT(p));
-	newval = inw(TCO1_CNT(p));
+	newval = inw(TCO1_CNT(p)) & ~NMI_NOW;
 
 	/* make sure the update is successful */
 	return val != newval ? -EIO : 0;
-- 
2.39.3

Re: [PATCH v3] iTCO_wdt: mask NMI_NOW bit for update_no_reboot_bit() call

Posted by Guenter Roeck 1 year, 3 months ago

On 9/13/24 12:14, Oleksandr Ocheretnyi wrote:
> Commit da23b6faa8bf ("watchdog: iTCO: Add support for Cannon Lake
> PCH iTCO") does not mask NMI_NOW bit during TCO1_CNT register's
> value comparison for update_no_reboot_bit() call causing following
> failure:
> 
>     ...
>     iTCO_vendor_support: vendor-support=0
>     iTCO_wdt iTCO_wdt: unable to reset NO_REBOOT flag, device
>                                      disabled by hardware/BIOS
>     ...
> 
> and this can lead to unexpected NMIs later during regular
> crashkernel's workflow because of watchdog probe call failures.
> 
> This change masks NMI_NOW bit for TCO1_CNT register values to
> avoid unexpected NMI_NOW bit inversions.
> 
> Fixes: da23b6faa8bf ("watchdog: iTCO: Add support for Cannon Lake PCH iTCO")
> Signed-off-by: Oleksandr Ocheretnyi <oocheret@cisco.com>

Reviewed-by: Guenter Roeck <linux@roeck-us.net>

> ---
>   V2 -> V3: Removed not necessary variable 'mask', updated multi-line comments
>   V1 -> V2: Provided comments and macro define with bit description
> 
>   drivers/watchdog/iTCO_wdt.c | 21 +++++++++++++++++++--
>   1 file changed, 19 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/watchdog/iTCO_wdt.c b/drivers/watchdog/iTCO_wdt.c
> index 264857d314da..dd297dcd524c 100644
> --- a/drivers/watchdog/iTCO_wdt.c
> +++ b/drivers/watchdog/iTCO_wdt.c
> @@ -82,6 +82,13 @@
>   #define TCO2_CNT(p)	(TCOBASE(p) + 0x0a) /* TCO2 Control Register	*/
>   #define TCOv2_TMR(p)	(TCOBASE(p) + 0x12) /* TCOv2 Timer Initial Value*/
>   
> +/*
> + * NMI_NOW is bit 8 of TCO1_CNT register
> + * Read/Write
> + * This bit is implemented as RW but has no effect on HW.
> + */
> +#define NMI_NOW		BIT(8)
> +
>   /* internal variables */
>   struct iTCO_wdt_private {
>   	struct watchdog_device wddev;
> @@ -219,13 +226,23 @@ static int update_no_reboot_bit_cnt(void *priv, bool set)
>   	struct iTCO_wdt_private *p = priv;
>   	u16 val, newval;
>   
> -	val = inw(TCO1_CNT(p));
> +	/*
> +	 * writing back 1b1 to NMI_NOW of TCO1_CNT register
> +	 * causes NMI_NOW bit inversion what consequently does
> +	 * not allow to perform the register's value comparison
> +	 * properly.
> +	 *
> +	 * NMI_NOW bit masking for TCO1_CNT register values
> +	 * helps to avoid possible NMI_NOW bit inversions on
> +	 * following write operation.
> +	 */
> +	val = inw(TCO1_CNT(p)) & ~NMI_NOW;
>   	if (set)
>   		val |= BIT(0);
>   	else
>   		val &= ~BIT(0);
>   	outw(val, TCO1_CNT(p));
> -	newval = inw(TCO1_CNT(p));
> +	newval = inw(TCO1_CNT(p)) & ~NMI_NOW;
>   
>   	/* make sure the update is successful */
>   	return val != newval ? -EIO : 0;

[PATCH v3] iTCO_wdt: mask NMI_NOW bit for update_no_reboot_bit() call

Posted by Oleksandr Ocheretnyi 1 year, 2 months ago

Hello Mika,

> I suggest adding some #define for the magical number 8 so that it is
> easier for anyone looking at this driver to figure out what it is doing.

Are the changes with #define NMI_NOW bit fine for you?

Best regards,
Oleksandr

Re: [PATCH v3] iTCO_wdt: mask NMI_NOW bit for update_no_reboot_bit() call

Posted by Mika Westerberg 1 year, 2 months ago

On Mon, Oct 07, 2024 at 08:57:02AM -0700, Oleksandr Ocheretnyi wrote:
> Hello Mika,
> 
> > I suggest adding some #define for the magical number 8 so that it is
> > easier for anyone looking at this driver to figure out what it is doing.
> 
> Are the changes with #define NMI_NOW bit fine for you?

Sure,

Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>

Re: [PATCH v2] iTCO_wdt: mask NMI_NOW bit for update_no_reboot_bit() call

Posted by Guenter Roeck 1 year, 3 months ago

On 9/12/24 07:19, Oleksandr Ocheretnyi wrote:
> Commit da23b6faa8bf ("watchdog: iTCO: Add support for Cannon Lake
> PCH iTCO") does not mask NMI_NOW bit during TCO1_CNT register's
> value comparison for update_no_reboot_bit() call causing following
> failure:
> 
>     ...
>     iTCO_vendor_support: vendor-support=0
>     iTCO_wdt iTCO_wdt: unable to reset NO_REBOOT flag, device
>                                      disabled by hardware/BIOS
>     ...
> 
> and this can lead to unexpected NMIs later during regular
> crashkernel's workflow because of watchdog probe call failures.
> 
> This change masks NMI_NOW bit for TCO1_CNT register values to
> avoid unexpected NMI_NOW bit inversions.
> 
> Fixes: da23b6faa8bf ("watchdog: iTCO: Add support for Cannon Lake PCH iTCO")
> Signed-off-by: Oleksandr Ocheretnyi <oocheret@cisco.com>
> ---
>   drivers/watchdog/iTCO_wdt.c | 23 +++++++++++++++++++----
>   1 file changed, 19 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/watchdog/iTCO_wdt.c b/drivers/watchdog/iTCO_wdt.c
> index 264857d314da..46c09359588f 100644
> --- a/drivers/watchdog/iTCO_wdt.c
> +++ b/drivers/watchdog/iTCO_wdt.c
> @@ -82,6 +82,12 @@
>   #define TCO2_CNT(p)	(TCOBASE(p) + 0x0a) /* TCO2 Control Register	*/
>   #define TCOv2_TMR(p)	(TCOBASE(p) + 0x12) /* TCOv2 Timer Initial Value*/
>   
> +/* NMI_NOW is bit 8 of TCO1_CNT register
> + * Read/Write
> + * This bit is implemented as RW but has no effect on HW.
> + */
> +#define NMI_NOW		BIT(8)
> +
>   /* internal variables */
>   struct iTCO_wdt_private {
>   	struct watchdog_device wddev;
> @@ -217,15 +223,24 @@ static int update_no_reboot_bit_mem(void *priv, bool set)
>   static int update_no_reboot_bit_cnt(void *priv, bool set)
>   {
>   	struct iTCO_wdt_private *p = priv;
> -	u16 val, newval;
> -
> -	val = inw(TCO1_CNT(p));
> +	u16 val, newval, mask = (~NMI_NOW);
> +
Unnecessary (). Either case, please just mask against ~NMI_NOW directly.
The mask variable is not necessary.

> +	/* writing back 1b1 to NMI_NOW of TCO1_CNT register

Standard multi-line comments, please.

Thanks,
Guenter

> +	 * causes NMI_NOW bit inversion what consequently does
> +	 * not allow to perform the register's value comparison
> +	 * properly.
> +	 *
> +	 * NMI_NOW bit masking for TCO1_CNT register values
> +	 * helps to avoid possible NMI_NOW bit inversions on
> +	 * following write operation.
> +	 */
> +	val = inw(TCO1_CNT(p)) & mask;
>   	if (set)
>   		val |= BIT(0);
>   	else
>   		val &= ~BIT(0);
>   	outw(val, TCO1_CNT(p));
> -	newval = inw(TCO1_CNT(p));
> +	newval = inw(TCO1_CNT(p)) & mask;
>   
>   	/* make sure the update is successful */
>   	return val != newval ? -EIO : 0;