[PATCH] backlight: lm3639: Unconditionally call led_classdev_unregister

[PATCH] backlight: lm3639: Unconditionally call led_classdev_unregister

[Nathan Chancellor]

Clang warns that the address of a pointer will always evaluated as true
in a boolean context.

drivers/video/backlight/lm3639_bl.c:403:14: warning: address of
'pchip->cdev_torch' will always evaluate to 'true'
[-Wpointer-bool-conversion]
        if (&pchip->cdev_torch)
        ~~   ~~~~~~~^~~~~~~~~~
drivers/video/backlight/lm3639_bl.c:405:14: warning: address of
'pchip->cdev_flash' will always evaluate to 'true'
[-Wpointer-bool-conversion]
        if (&pchip->cdev_flash)
        ~~   ~~~~~~~^~~~~~~~~~
2 warnings generated.

These statements have been present since 2012, introduced by
commit 0f59858d5119 ("backlight: add new lm3639 backlight
driver"). Given that they have been called unconditionally since
then presumably without any issues, removing the always true if
statements to fix the warnings without any real world changes.

Link: https://github.com/ClangBuiltLinux/linux/issues/119
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
---

Alternatively, it's possible the address wasn't supposed to be taken or
the dev in these structs should be checked instead. I don't have this
hardware to make that call so I would appreciate some review and
opinions on what was intended here.

Thanks!

 drivers/video/backlight/lm3639_bl.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/video/backlight/lm3639_bl.c b/drivers/video/backlight/lm3639_bl.c
index cd50df5807ea..086611c7bc03 100644
--- a/drivers/video/backlight/lm3639_bl.c
+++ b/drivers/video/backlight/lm3639_bl.c
@@ -400,10 +400,8 @@ static int lm3639_remove(struct i2c_client *client)
 
 	regmap_write(pchip->regmap, REG_ENABLE, 0x00);
 
-	if (&pchip->cdev_torch)
-		led_classdev_unregister(&pchip->cdev_torch);
-	if (&pchip->cdev_flash)
-		led_classdev_unregister(&pchip->cdev_flash);
+	led_classdev_unregister(&pchip->cdev_torch);
+	led_classdev_unregister(&pchip->cdev_flash);
 	if (pchip->bled)
 		device_remove_file(&(pchip->bled->dev), &dev_attr_bled_mode);
 	return 0;
-- 
2.19.0

Re: [PATCH] backlight: lm3639: Unconditionally call led_classdev_unregister

[Nick Desaulniers]

On Fri, Sep 21, 2018 at 1:23 PM Nathan Chancellor
<natechancellor@gmail.com> wrote:
>
> Clang warns that the address of a pointer will always evaluated as true
> in a boolean context.
>
> drivers/video/backlight/lm3639_bl.c:403:14: warning: address of
> 'pchip->cdev_torch' will always evaluate to 'true'
> [-Wpointer-bool-conversion]
>         if (&pchip->cdev_torch)
>         ~~   ~~~~~~~^~~~~~~~~~
> drivers/video/backlight/lm3639_bl.c:405:14: warning: address of
> 'pchip->cdev_flash' will always evaluate to 'true'
> [-Wpointer-bool-conversion]
>         if (&pchip->cdev_flash)
>         ~~   ~~~~~~~^~~~~~~~~~
> 2 warnings generated.
>
> These statements have been present since 2012, introduced by
> commit 0f59858d5119 ("backlight: add new lm3639 backlight
> driver"). Given that they have been called unconditionally since
> then presumably without any issues, removing the always true if
> statements to fix the warnings without any real world changes.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/119
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
> ---
>
> Alternatively, it's possible the address wasn't supposed to be taken or
> the dev in these structs should be checked instead. I don't have this
> hardware to make that call so I would appreciate some review and
> opinions on what was intended here.
>
> Thanks!
>
>  drivers/video/backlight/lm3639_bl.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/video/backlight/lm3639_bl.c b/drivers/video/backlight/lm3639_bl.c
> index cd50df5807ea..086611c7bc03 100644
> --- a/drivers/video/backlight/lm3639_bl.c
> +++ b/drivers/video/backlight/lm3639_bl.c
> @@ -400,10 +400,8 @@ static int lm3639_remove(struct i2c_client *client)
>
>         regmap_write(pchip->regmap, REG_ENABLE, 0x00);
>
> -       if (&pchip->cdev_torch)
> -               led_classdev_unregister(&pchip->cdev_torch);
> -       if (&pchip->cdev_flash)
> -               led_classdev_unregister(&pchip->cdev_flash);
> +       led_classdev_unregister(&pchip->cdev_torch);
> +       led_classdev_unregister(&pchip->cdev_flash);

led_classdev_unregister() requires that its arg is non-null (as it
dereferences it without any kind of check).  It's not clear that
i2c_get_clientdata() can never return a null pointer, so I think all
references to pchip in this function should instead be guarded with a
null check.  Would you mind making that change and sending a v2?

>         if (pchip->bled)
>                 device_remove_file(&(pchip->bled->dev), &dev_attr_bled_mode);
>         return 0;
> --
> 2.19.0
>


-- 
Thanks,
~Nick Desaulniers

Re: [PATCH] backlight: lm3639: Unconditionally call led_classdev_unregister

[Nathan Chancellor]

On Fri, Sep 21, 2018 at 03:48:50PM -0700, Nick Desaulniers wrote:
> On Fri, Sep 21, 2018 at 1:23 PM Nathan Chancellor
> <natechancellor@gmail.com> wrote:
> >
> > Clang warns that the address of a pointer will always evaluated as true
> > in a boolean context.
> >
> > drivers/video/backlight/lm3639_bl.c:403:14: warning: address of
> > 'pchip->cdev_torch' will always evaluate to 'true'
> > [-Wpointer-bool-conversion]
> >         if (&pchip->cdev_torch)
> >         ~~   ~~~~~~~^~~~~~~~~~
> > drivers/video/backlight/lm3639_bl.c:405:14: warning: address of
> > 'pchip->cdev_flash' will always evaluate to 'true'
> > [-Wpointer-bool-conversion]
> >         if (&pchip->cdev_flash)
> >         ~~   ~~~~~~~^~~~~~~~~~
> > 2 warnings generated.
> >
> > These statements have been present since 2012, introduced by
> > commit 0f59858d5119 ("backlight: add new lm3639 backlight
> > driver"). Given that they have been called unconditionally since
> > then presumably without any issues, removing the always true if
> > statements to fix the warnings without any real world changes.
> >
> > Link: https://github.com/ClangBuiltLinux/linux/issues/119
> > Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
> > ---
> >
> > Alternatively, it's possible the address wasn't supposed to be taken or
> > the dev in these structs should be checked instead. I don't have this
> > hardware to make that call so I would appreciate some review and
> > opinions on what was intended here.
> >
> > Thanks!
> >
> >  drivers/video/backlight/lm3639_bl.c | 6 ++----
> >  1 file changed, 2 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/video/backlight/lm3639_bl.c b/drivers/video/backlight/lm3639_bl.c
> > index cd50df5807ea..086611c7bc03 100644
> > --- a/drivers/video/backlight/lm3639_bl.c
> > +++ b/drivers/video/backlight/lm3639_bl.c
> > @@ -400,10 +400,8 @@ static int lm3639_remove(struct i2c_client *client)
> >
> >         regmap_write(pchip->regmap, REG_ENABLE, 0x00);
> >
> > -       if (&pchip->cdev_torch)
> > -               led_classdev_unregister(&pchip->cdev_torch);
> > -       if (&pchip->cdev_flash)
> > -               led_classdev_unregister(&pchip->cdev_flash);
> > +       led_classdev_unregister(&pchip->cdev_torch);
> > +       led_classdev_unregister(&pchip->cdev_flash);
> 
> led_classdev_unregister() requires that its arg is non-null (as it
> dereferences it without any kind of check).  It's not clear that
> i2c_get_clientdata() can never return a null pointer, so I think all
> references to pchip in this function should instead be guarded with a
> null check.  Would you mind making that change and sending a v2?
> 

Hi Nick,

I did a quick grep throughout the tree and I didn't see any place where
there were null checks for i2c_get_clientdata, leading me to believe
that such a check isn't necessary although I am nowhere close to an expert
into this stuff. I'm not sure I follow the rest of the request though,
where should the check be? Before regmap_write?

Furthermore, the probe function seems to make sure all of these get
initialized properly, doesn't remove imply that probe was successful?

Thank you for the comment and review!
Nathan

> >         if (pchip->bled)
> >                 device_remove_file(&(pchip->bled->dev), &dev_attr_bled_mode);
> >         return 0;
> > --
> > 2.19.0
> >
> 
> 
> -- 
> Thanks,
> ~Nick Desaulniers

Re: [PATCH] backlight: lm3639: Unconditionally call led_classdev_unregister

[Nick Desaulniers]

On Fri, Sep 21, 2018 at 4:10 PM Nathan Chancellor
<natechancellor@gmail.com> wrote:
>
> On Fri, Sep 21, 2018 at 03:48:50PM -0700, Nick Desaulniers wrote:
> > On Fri, Sep 21, 2018 at 1:23 PM Nathan Chancellor
> > <natechancellor@gmail.com> wrote:
> > >
> > > Clang warns that the address of a pointer will always evaluated as true
> > > in a boolean context.
> > >
> > > drivers/video/backlight/lm3639_bl.c:403:14: warning: address of
> > > 'pchip->cdev_torch' will always evaluate to 'true'
> > > [-Wpointer-bool-conversion]
> > >         if (&pchip->cdev_torch)
> > >         ~~   ~~~~~~~^~~~~~~~~~
> > > drivers/video/backlight/lm3639_bl.c:405:14: warning: address of
> > > 'pchip->cdev_flash' will always evaluate to 'true'
> > > [-Wpointer-bool-conversion]
> > >         if (&pchip->cdev_flash)
> > >         ~~   ~~~~~~~^~~~~~~~~~
> > > 2 warnings generated.
> > >
> > > These statements have been present since 2012, introduced by
> > > commit 0f59858d5119 ("backlight: add new lm3639 backlight
> > > driver"). Given that they have been called unconditionally since
> > > then presumably without any issues, removing the always true if
> > > statements to fix the warnings without any real world changes.
> > >
> > > Link: https://github.com/ClangBuiltLinux/linux/issues/119
> > > Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
> > > ---
> > >
> > > Alternatively, it's possible the address wasn't supposed to be taken or
> > > the dev in these structs should be checked instead. I don't have this
> > > hardware to make that call so I would appreciate some review and
> > > opinions on what was intended here.
> > >
> > > Thanks!
> > >
> > >  drivers/video/backlight/lm3639_bl.c | 6 ++----
> > >  1 file changed, 2 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/video/backlight/lm3639_bl.c b/drivers/video/backlight/lm3639_bl.c
> > > index cd50df5807ea..086611c7bc03 100644
> > > --- a/drivers/video/backlight/lm3639_bl.c
> > > +++ b/drivers/video/backlight/lm3639_bl.c
> > > @@ -400,10 +400,8 @@ static int lm3639_remove(struct i2c_client *client)
> > >
> > >         regmap_write(pchip->regmap, REG_ENABLE, 0x00);
> > >
> > > -       if (&pchip->cdev_torch)
> > > -               led_classdev_unregister(&pchip->cdev_torch);
> > > -       if (&pchip->cdev_flash)
> > > -               led_classdev_unregister(&pchip->cdev_flash);
> > > +       led_classdev_unregister(&pchip->cdev_torch);
> > > +       led_classdev_unregister(&pchip->cdev_flash);
> >
> > led_classdev_unregister() requires that its arg is non-null (as it
> > dereferences it without any kind of check).  It's not clear that
> > i2c_get_clientdata() can never return a null pointer, so I think all
> > references to pchip in this function should instead be guarded with a
> > null check.  Would you mind making that change and sending a v2?
> >
>
> Hi Nick,
>
> I did a quick grep throughout the tree and I didn't see any place where
> there were null checks for i2c_get_clientdata, leading me to believe
> that such a check isn't necessary although I am nowhere close to an expert
> into this stuff.

This seems to be the case.  We should start using
__attribute__((returns_nonnull)) (gated on gcc 5+).
I *think* that the device's driver_data is actually set in
drivers/video/backlight/backlight.c.  Looks like
CONFIG_BACKLIGHT_LM3639 depends on CONFIG_BACKLIGHT_CLASS_DEVICE so I
feel more confident in your patch.
I would still prefer the maintainers to review though.

> I'm not sure I follow the rest of the request though,
> where should the check be? Before regmap_write?
>
> Furthermore, the probe function seems to make sure all of these get
> initialized properly, doesn't remove imply that probe was successful?
>
> Thank you for the comment and review!
> Nathan
>
> > >         if (pchip->bled)
> > >                 device_remove_file(&(pchip->bled->dev), &dev_attr_bled_mode);
> > >         return 0;
> > > --
> > > 2.19.0
> > >
> >
> >
> > --
> > Thanks,
> > ~Nick Desaulniers



-- 
Thanks,
~Nick Desaulniers

Re: [PATCH] backlight: lm3639: Unconditionally call led_classdev_unregister

[Daniel Thompson]

On Mon, Sep 24, 2018 at 02:41:04PM -0700, Nick Desaulniers wrote:
> On Fri, Sep 21, 2018 at 4:10 PM Nathan Chancellor
> <natechancellor@gmail.com> wrote:
> >
> > On Fri, Sep 21, 2018 at 03:48:50PM -0700, Nick Desaulniers wrote:
> > > On Fri, Sep 21, 2018 at 1:23 PM Nathan Chancellor
> > > <natechancellor@gmail.com> wrote:
> > > >
> > > > Clang warns that the address of a pointer will always evaluated as true
> > > > in a boolean context.
> > > >
> > > > drivers/video/backlight/lm3639_bl.c:403:14: warning: address of
> > > > 'pchip->cdev_torch' will always evaluate to 'true'
> > > > [-Wpointer-bool-conversion]
> > > >         if (&pchip->cdev_torch)
> > > >         ~~   ~~~~~~~^~~~~~~~~~
> > > > drivers/video/backlight/lm3639_bl.c:405:14: warning: address of
> > > > 'pchip->cdev_flash' will always evaluate to 'true'
> > > > [-Wpointer-bool-conversion]
> > > >         if (&pchip->cdev_flash)
> > > >         ~~   ~~~~~~~^~~~~~~~~~
> > > > 2 warnings generated.
> > > >
> > > > These statements have been present since 2012, introduced by
> > > > commit 0f59858d5119 ("backlight: add new lm3639 backlight
> > > > driver"). Given that they have been called unconditionally since
> > > > then presumably without any issues, removing the always true if
> > > > statements to fix the warnings without any real world changes.
> > > >
> > > > Link: https://github.com/ClangBuiltLinux/linux/issues/119
> > > > Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>

Based on conversation below...

Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>


> > > > ---
> > > >
> > > > Alternatively, it's possible the address wasn't supposed to be taken or
> > > > the dev in these structs should be checked instead. I don't have this
> > > > hardware to make that call so I would appreciate some review and
> > > > opinions on what was intended here.
> > > >
> > > > Thanks!
> > > >
> > > >  drivers/video/backlight/lm3639_bl.c | 6 ++----
> > > >  1 file changed, 2 insertions(+), 4 deletions(-)
> > > >
> > > > diff --git a/drivers/video/backlight/lm3639_bl.c b/drivers/video/backlight/lm3639_bl.c
> > > > index cd50df5807ea..086611c7bc03 100644
> > > > --- a/drivers/video/backlight/lm3639_bl.c
> > > > +++ b/drivers/video/backlight/lm3639_bl.c
> > > > @@ -400,10 +400,8 @@ static int lm3639_remove(struct i2c_client *client)
> > > >
> > > >         regmap_write(pchip->regmap, REG_ENABLE, 0x00);
> > > >
> > > > -       if (&pchip->cdev_torch)
> > > > -               led_classdev_unregister(&pchip->cdev_torch);
> > > > -       if (&pchip->cdev_flash)
> > > > -               led_classdev_unregister(&pchip->cdev_flash);
> > > > +       led_classdev_unregister(&pchip->cdev_torch);
> > > > +       led_classdev_unregister(&pchip->cdev_flash);
> > >
> > > led_classdev_unregister() requires that its arg is non-null (as it
> > > dereferences it without any kind of check).  It's not clear that
> > > i2c_get_clientdata() can never return a null pointer, so I think all
> > > references to pchip in this function should instead be guarded with a
> > > null check.  Would you mind making that change and sending a v2?
> > >
> >
> > Hi Nick,
> >
> > I did a quick grep throughout the tree and I didn't see any place where
> > there were null checks for i2c_get_clientdata, leading me to believe
> > that such a check isn't necessary although I am nowhere close to an expert
> > into this stuff.
> 
> This seems to be the case.  We should start using
> __attribute__((returns_nonnull)) (gated on gcc 5+).
> I *think* that the device's driver_data is actually set in
> drivers/video/backlight/backlight.c.  Looks like
> CONFIG_BACKLIGHT_LM3639 depends on CONFIG_BACKLIGHT_CLASS_DEVICE so I
> feel more confident in your patch.
> I would still prefer the maintainers to review though.

AFAICT it is impossible for the probe function to complete
successfully without having called i2c_set_clientdata()
and therefore it is impossible for pchip to be NULL
in the remove function.

Not sure it is possible to use return_nonnull though. It is not that
i2c_get_clientdata() can *never* return non-NULL, it is that in *this*
case (which is actually a fairly common one) it can never return
non-NULL.


Daniel.

Re: [PATCH] backlight: lm3639: Unconditionally call led_classdev_unregister

[Lee Jones]

On Fri, 21 Sep 2018, Nathan Chancellor wrote:

> Clang warns that the address of a pointer will always evaluated as true
> in a boolean context.
> 
> drivers/video/backlight/lm3639_bl.c:403:14: warning: address of
> 'pchip->cdev_torch' will always evaluate to 'true'
> [-Wpointer-bool-conversion]
>         if (&pchip->cdev_torch)
>         ~~   ~~~~~~~^~~~~~~~~~
> drivers/video/backlight/lm3639_bl.c:405:14: warning: address of
> 'pchip->cdev_flash' will always evaluate to 'true'
> [-Wpointer-bool-conversion]
>         if (&pchip->cdev_flash)
>         ~~   ~~~~~~~^~~~~~~~~~
> 2 warnings generated.
> 
> These statements have been present since 2012, introduced by
> commit 0f59858d5119 ("backlight: add new lm3639 backlight
> driver"). Given that they have been called unconditionally since
> then presumably without any issues, removing the always true if
> statements to fix the warnings without any real world changes.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/119
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
> ---
> 
> Alternatively, it's possible the address wasn't supposed to be taken or
> the dev in these structs should be checked instead. I don't have this
> hardware to make that call so I would appreciate some review and
> opinions on what was intended here.
> 
> Thanks!
> 
>  drivers/video/backlight/lm3639_bl.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)

Applied, thanks.

-- 
Lee Jones [李琼斯]
Linaro Services Technical Lead
Linaro.org │ Open source software for ARM SoCs
Follow Linaro: Facebook | Twitter | Blog