[PATCH] Revert "venus: pm_helpers: Fix error check in vcodec_domains_get()"

[PATCH] Revert "venus: pm_helpers: Fix error check in vcodec_domains_get()"

[Dan Carpenter]

This reverts commit 0f6e8d8c94a82e85e1b9b62a7671990740dc6f70.

The reverted commit was based on static analysis and a misunderstanding
of how PTR_ERR() and NULLs are supposed to work.  When a function
returns both pointer errors and NULL then normally the NULL means
"continue operating without a feature because it was deliberately
turned off".  The NULL should not be treated as a failure.  If a driver
cannot work when that feature is disabled then the KConfig should
enforce that the function cannot return NULL.  We should not need to
test for it.

In this code, the patch breaks the venus driver if CONFIG_PM is
disabled.

Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
---
This patch is also based on static analysis and review so probably best
to be cautious.  My guess is that very few people disable CONFIG_PM
these days so that's why the bug wasn't caught.

 drivers/media/platform/qcom/venus/pm_helpers.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/media/platform/qcom/venus/pm_helpers.c b/drivers/media/platform/qcom/venus/pm_helpers.c
index 48c9084bb4db..c93d2906e4c7 100644
--- a/drivers/media/platform/qcom/venus/pm_helpers.c
+++ b/drivers/media/platform/qcom/venus/pm_helpers.c
@@ -869,8 +869,8 @@ static int vcodec_domains_get(struct venus_core *core)
 	for (i = 0; i < res->vcodec_pmdomains_num; i++) {
 		pd = dev_pm_domain_attach_by_name(dev,
 						  res->vcodec_pmdomains[i]);
-		if (IS_ERR_OR_NULL(pd))
-			return PTR_ERR(pd) ? : -ENODATA;
+		if (IS_ERR(pd))
+			return PTR_ERR(pd);
 		core->pmdomains[i] = pd;
 	}
 
-- 
2.39.2

Re: [PATCH] Revert "venus: pm_helpers: Fix error check in vcodec_domains_get()"

[Vikash Garodia]

Hi Dan,

On 7/3/2023 9:00 PM, Dan Carpenter wrote:
> This reverts commit 0f6e8d8c94a82e85e1b9b62a7671990740dc6f70.
> 
> The reverted commit was based on static analysis and a misunderstanding
> of how PTR_ERR() and NULLs are supposed to work.  When a function
> returns both pointer errors and NULL then normally the NULL means
> "continue operating without a feature because it was deliberately
> turned off".  The NULL should not be treated as a failure.  If a driver
> cannot work when that feature is disabled then the KConfig should
> enforce that the function cannot return NULL.  We should not need to
> test for it.
> 
> In this code, the patch breaks the venus driver if CONFIG_PM is
> disabled.
> 
> Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
> ---
> This patch is also based on static analysis and review so probably best
> to be cautious.  My guess is that very few people disable CONFIG_PM
> these days so that's why the bug wasn't caught.
> 
>  drivers/media/platform/qcom/venus/pm_helpers.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/media/platform/qcom/venus/pm_helpers.c b/drivers/media/platform/qcom/venus/pm_helpers.c
> index 48c9084bb4db..c93d2906e4c7 100644
> --- a/drivers/media/platform/qcom/venus/pm_helpers.c
> +++ b/drivers/media/platform/qcom/venus/pm_helpers.c
> @@ -869,8 +869,8 @@ static int vcodec_domains_get(struct venus_core *core)
>  	for (i = 0; i < res->vcodec_pmdomains_num; i++) {
>  		pd = dev_pm_domain_attach_by_name(dev,
>  						  res->vcodec_pmdomains[i]);
> -		if (IS_ERR_OR_NULL(pd))
> -			return PTR_ERR(pd) ? : -ENODATA;
> +		if (IS_ERR(pd))
> +			return PTR_ERR(pd);
Trying to understand if pm domains for Venus (pd) is returned NULL here, how
would the driver be able to enable and disable those power domains at [1]. And
without that, video usecase would be functional ?

[1]
https://elixir.bootlin.com/linux/latest/source/drivers/media/platform/qcom/venus/pm_helpers.c#L1043

>  		core->pmdomains[i] = pd;
>  	}
> 

Re: [PATCH] Revert "venus: pm_helpers: Fix error check in vcodec_domains_get()"

[Dan Carpenter]

On Mon, Jul 10, 2023 at 12:59:22PM +0530, Vikash Garodia wrote:
> Hi Dan,
> 
> On 7/3/2023 9:00 PM, Dan Carpenter wrote:
> > This reverts commit 0f6e8d8c94a82e85e1b9b62a7671990740dc6f70.
> > 
> > The reverted commit was based on static analysis and a misunderstanding
> > of how PTR_ERR() and NULLs are supposed to work.  When a function
> > returns both pointer errors and NULL then normally the NULL means
> > "continue operating without a feature because it was deliberately
> > turned off".  The NULL should not be treated as a failure.  If a driver
> > cannot work when that feature is disabled then the KConfig should
> > enforce that the function cannot return NULL.  We should not need to
> > test for it.
> > 
> > In this code, the patch breaks the venus driver if CONFIG_PM is
> > disabled.
> > 
> > Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
> > ---
> > This patch is also based on static analysis and review so probably best
> > to be cautious.  My guess is that very few people disable CONFIG_PM
> > these days so that's why the bug wasn't caught.
> > 
> >  drivers/media/platform/qcom/venus/pm_helpers.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/media/platform/qcom/venus/pm_helpers.c b/drivers/media/platform/qcom/venus/pm_helpers.c
> > index 48c9084bb4db..c93d2906e4c7 100644
> > --- a/drivers/media/platform/qcom/venus/pm_helpers.c
> > +++ b/drivers/media/platform/qcom/venus/pm_helpers.c
> > @@ -869,8 +869,8 @@ static int vcodec_domains_get(struct venus_core *core)
> >  	for (i = 0; i < res->vcodec_pmdomains_num; i++) {
> >  		pd = dev_pm_domain_attach_by_name(dev,
> >  						  res->vcodec_pmdomains[i]);
> > -		if (IS_ERR_OR_NULL(pd))
> > -			return PTR_ERR(pd) ? : -ENODATA;
> > +		if (IS_ERR(pd))
> > +			return PTR_ERR(pd);
> Trying to understand if pm domains for Venus (pd) is returned NULL here, how
> would the driver be able to enable and disable those power domains at [1]. And
> without that, video usecase would be functional ?
> 
> [1]
> https://elixir.bootlin.com/linux/latest/source/drivers/media/platform/qcom/venus/pm_helpers.c#L1043

I don't understand.  The CONFIG_PM is Power Management.  If you
deliberately disable power management then then, obviously, power
domains are not going to be enabled.  The __pm_runtime_resume() function
turns into:

include/linux/pm_runtime.h
   268  static inline int __pm_runtime_resume(struct device *dev, int rpmflags)
   269  {
   270          return 1;
   271  }

In real life, most people are going to want power management.

This is a video accelerator.  I would expect that it could still work
without power management.  If it really can't then that should be
enforced in the Kconfig.  Having this code here which says "We can't
load without CONFIG_PM" is wrong, it should be "We can't compile without
CONFIG_PM".

regards,
dan carpenter

Re: [PATCH] Revert "venus: pm_helpers: Fix error check in vcodec_domains_get()"

[Vikash Garodia]

On 7/10/2023 1:33 PM, Dan Carpenter wrote:
> On Mon, Jul 10, 2023 at 12:59:22PM +0530, Vikash Garodia wrote:
>> Hi Dan,
>>
>> On 7/3/2023 9:00 PM, Dan Carpenter wrote:
>>> This reverts commit 0f6e8d8c94a82e85e1b9b62a7671990740dc6f70.
>>>
>>> The reverted commit was based on static analysis and a misunderstanding
>>> of how PTR_ERR() and NULLs are supposed to work.  When a function
>>> returns both pointer errors and NULL then normally the NULL means
>>> "continue operating without a feature because it was deliberately
>>> turned off".  The NULL should not be treated as a failure.  If a driver
>>> cannot work when that feature is disabled then the KConfig should
>>> enforce that the function cannot return NULL.  We should not need to
>>> test for it.
>>>
>>> In this code, the patch breaks the venus driver if CONFIG_PM is
>>> disabled.
>>>
>>> Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
>>> ---
>>> This patch is also based on static analysis and review so probably best
>>> to be cautious.  My guess is that very few people disable CONFIG_PM
>>> these days so that's why the bug wasn't caught.
>>>
>>>  drivers/media/platform/qcom/venus/pm_helpers.c | 4 ++--
>>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/media/platform/qcom/venus/pm_helpers.c b/drivers/media/platform/qcom/venus/pm_helpers.c
>>> index 48c9084bb4db..c93d2906e4c7 100644
>>> --- a/drivers/media/platform/qcom/venus/pm_helpers.c
>>> +++ b/drivers/media/platform/qcom/venus/pm_helpers.c
>>> @@ -869,8 +869,8 @@ static int vcodec_domains_get(struct venus_core *core)
>>>  	for (i = 0; i < res->vcodec_pmdomains_num; i++) {
>>>  		pd = dev_pm_domain_attach_by_name(dev,
>>>  						  res->vcodec_pmdomains[i]);
>>> -		if (IS_ERR_OR_NULL(pd))
>>> -			return PTR_ERR(pd) ? : -ENODATA;
>>> +		if (IS_ERR(pd))
>>> +			return PTR_ERR(pd);
>> Trying to understand if pm domains for Venus (pd) is returned NULL here, how
>> would the driver be able to enable and disable those power domains at [1]. And
>> without that, video usecase would be functional ?
>>
>> [1]
>> https://elixir.bootlin.com/linux/latest/source/drivers/media/platform/qcom/venus/pm_helpers.c#L1043
> 
> I don't understand.  The CONFIG_PM is Power Management.  If you
> deliberately disable power management then then, obviously, power
> domains are not going to be enabled.  The __pm_runtime_resume() function
> turns into:
> 
> include/linux/pm_runtime.h
>    268  static inline int __pm_runtime_resume(struct device *dev, int rpmflags)
>    269  {
>    270          return 1;
>    271  }
> 
> In real life, most people are going to want power management.
> 
> This is a video accelerator.  I would expect that it could still work
> without power management.
It won't, without those 2 power domains enabled for Venus. Does it work for you
when you disabled the config ?

  If it really can't then that should be
> enforced in the Kconfig.  Having this code here which says "We can't
> load without CONFIG_PM" is wrong, it should be "We can't compile without
> CONFIG_PM".

Its better enforced in Kconfig. By allowing NULL for
dev_pm_domain_attach_by_name does not still indicate that the functionality is
dependent on CONFIG_PM to be enabled.

Thanks,
Vikash

Re: [PATCH] Revert "venus: pm_helpers: Fix error check in vcodec_domains_get()"

[Dan Carpenter]

On Mon, Jul 10, 2023 at 01:48:52PM +0530, Vikash Garodia wrote:
> > This is a video accelerator.  I would expect that it could still work
> > without power management.
> It won't, without those 2 power domains enabled for Venus. Does it work for you
> when you disabled the config ?

I have not tested this, I'm reviewing static checker bugs, as I
explained here:

> >>> This patch is also based on static analysis and review so probably best
> >>> to be cautious.  My guess is that very few people disable CONFIG_PM
> >>> these days so that's why the bug wasn't caught.


> Its better enforced in Kconfig. By allowing NULL for
> dev_pm_domain_attach_by_name does not still indicate that the functionality is
> dependent on CONFIG_PM to be enabled.

The way I'm writing it is the correct way.  I explain this better in
my blog.

https://staticthinking.wordpress.com/2022/08/01/mixing-error-pointers-and-null/

Currently it looks like the Kconfig does not have a dependency on
CONFIG_PM.  If we fix the the Kconfig, but leave the "harmless" bug here
then it will still show up as a static checker warning when COMPILE_TEST
is enabled.

We should just do it in the correct way even after we fix the Kconfig.

regards,
dan carpenter