Re: REGRESSION: [RESEND PATCH v3 1/4] backlight: pwm_bl: linear interpolation between brightness-levels

[Marcel Ziswiler <marcel.ziswiler@toradex.com>]

On Mon, 2018-07-16 at 10:42 +0100, Daniel Thompson wrote:
> On Sun, Jul 15, 2018 at 02:26:44PM +0000, Marcel Ziswiler wrote:
> > On Sun, 2018-07-15 at 08:57 +0100, Daniel Thompson wrote:
> > > On Sat, Jul 14, 2018 at 03:08:17PM +0000, Marcel Ziswiler wrote:
> > > > On Mon, 2018-04-09 at 10:33 +0200, Enric Balletbo i Serra
> > > > wrote:
> > > > > diff --git a/drivers/video/backlight/pwm_bl.c
> > > > > b/drivers/video/backlight/pwm_bl.c
> > > > > index 8e3f1245f5c5..f0a108ab570a 100644
> > > > > --- a/drivers/video/backlight/pwm_bl.c
> > > > > +++ b/drivers/video/backlight/pwm_bl.c
> > > > > @@ -147,7 +147,11 @@ static int pwm_backlight_parse_dt(struct
> > > > > device
> > > > > *dev,
> > > > >  				  struct
> > > > > platform_pwm_backlight_data
> > > > > *data)
> > > > >  {
> > > > >  	struct device_node *node = dev->of_node;
> > > > > +	unsigned int num_levels = 0;
> > > > > +	unsigned int levels_count;
> > > > > +	unsigned int num_steps;
> > > 
> > > num_steps is not initialized...
> > > 
> > > 
> > > > >  	struct property *prop;
> > > > > +	unsigned int *table;
> > > > >  	int length;
> > > > >  	u32 value;
> > > > >  	int ret;
> > > > > @@ -167,6 +171,7 @@ static int pwm_backlight_parse_dt(struct
> > > > > device
> > > > > *dev,
> > > > >  	/* read brightness levels from DT property */
> > > > >  	if (data->max_brightness > 0) {
> > > > >  		size_t size = sizeof(*data->levels) * data-
> > > > > > max_brightness;
> > > > > 
> > > > > +		unsigned int i, j, n = 0;
> > > > >  
> > > > >  		data->levels = devm_kzalloc(dev, size,
> > > > > GFP_KERNEL);
> > > > >  		if (!data->levels)
> > > > > @@ -184,6 +189,84 @@ static int pwm_backlight_parse_dt(struct
> > > > > device
> > > > > *dev,
> > > > >  			return ret;
> > > > >  
> > > > >  		data->dft_brightness = value;
> > > > > +
> > > > > +		/*
> > > > > +		 * This property is optional, if is set
> > > > > enables
> > > > > linear
> > > > > +		 * interpolation between each of the values
> > > > > of
> > > > > brightness levels
> > > > > +		 * and creates a new pre-computed table.
> > > > > +		 */
> > > > > +		of_property_read_u32(node, "num-
> > > > > interpolated-
> > > > > steps",
> > > > > +				     &num_steps);
> > > 
> > > ... this is not guaranteed to initialized num_steps ...
> > 
> > Yes, as it only does so if returning zero. I do further propose to
> > check its return value as well. Isn't that what return values are
> > used
> > for?
> 
> I don't much mind either way.
> 
> I originally wrote the patch you shared below but then decided to ask
> you
> to test and, since I didn't compile test before doing so, I opted for
> something more immune to silly mistakes.
> 
> 
> > Quoting from include/linux/of.h:
> > 
> > Search for a property in a device node and read 32-bit value(s)
> > from
> > it. Returns 0 on success, -EINVAL if the property does not exist,
> > -ENODATA if property does not have a value, and -EOVERFLOW if the
> > property data isn't large enough.
> > 
> > > > > +
> > > > > +		/*
> > > > > +		 * Make sure that there is at least two
> > > > > entries
> > > > > in
> > > > > the
> > > > > +		 * brightness-levels table, otherwise we
> > > > > can't
> > > > > interpolate
> > > > > +		 * between two points.
> > > > > +		 */
> > > > > +		if (num_steps) {
> > > 
> > > ... and we make a decision on it here.
> > > 
> > > Marcel: Can you try the following quick fix? It's untested on my
> > > side
> > >         but very simple...
> > > 
> > > From 6fa2fbeb017086147ac61981107a95cb8ae7b4e7 Mon Sep 17 00:00:00
> > > 2001
> > > From: Daniel Thompson <daniel.thompson@linaro.org>
> > > Date: Sun, 15 Jul 2018 08:49:05 +0100
> > > Subject: [PATCH] backlight: pwm_bl: Fix uninitialized variable
> > > 
> > > Currently, if the DT does not define num-interpolated-steps then
> > > num_steps is undefined meaning the interpolation code will deploy
> > > randomly. Fix this.
> > > 
> > > Fixes: 573fe6d1c25c ("backlight: pwm_bl: Linear interpolation
> > > between
> > > brightness-levels")
> > > Reported-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
> > > Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
> > > ---
> > >  drivers/video/backlight/pwm_bl.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/video/backlight/pwm_bl.c
> > > b/drivers/video/backlight/pwm_bl.c
> > > index 9ee4c1b735b2..bdfcc0a71db1 100644
> > > --- a/drivers/video/backlight/pwm_bl.c
> > > +++ b/drivers/video/backlight/pwm_bl.c
> > > @@ -250,7 +250,7 @@ static int pwm_backlight_parse_dt(struct
> > > device
> > > *dev,
> > >  	struct device_node *node = dev->of_node;
> > >  	unsigned int num_levels = 0;
> > >  	unsigned int levels_count;
> > > -	unsigned int num_steps;
> > > +	unsigned int num_steps = 0;
> > >  	struct property *prop;
> > >  	unsigned int *table;
> > >  	int length;
> > > --
> > > 2.17.1
> > 
> > From dbb31d00c9f2873affedbceae917c9d7fce5f832 Mon Sep 17 00:00:00
> > 2001
> > Message-Id:
> > <dbb31d00c9f2873affedbceae917c9d7fce5f832.1531664663.git.ma
> > rcel.ziswiler@toradex.com>
> > From: Daniel Thompson <daniel.thompson@linaro.org>
> > Date: Sun, 15 Jul 2018 08:49:05 +0100
> > Subject: [PATCH] backlight: pwm_bl: Fix uninitialized variable
> > 
> > Currently, if the DT does not define num-interpolated-steps then
> > num_steps is undefined meaning the interpolation code will deploy
> > randomly. Fix this.
> > 
> > Fixes: 573fe6d1c25c ("backlight: pwm_bl: Linear interpolation
> > between
> > brightness-levels")
> > Reported-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
> > Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
> > Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
> 
> Is it Tested-by: too? It would be good to confirm I was right about
> the
> cause of the problem.

Yes and I confirm you were right.

> > ---
> >  drivers/video/backlight/pwm_bl.c | 18 ++++++++----------
> >  1 file changed, 8 insertions(+), 10 deletions(-)
> > 
> > diff --git a/drivers/video/backlight/pwm_bl.c
> > b/drivers/video/backlight/pwm_bl.c
> > index 9ee4c1b735b2..e884d589378d 100644
> > --- a/drivers/video/backlight/pwm_bl.c
> > +++ b/drivers/video/backlight/pwm_bl.c
> > @@ -250,7 +250,7 @@ static int pwm_backlight_parse_dt(struct device
> > *dev,
> >  	struct device_node *node = dev->of_node;
> >  	unsigned int num_levels = 0;
> >  	unsigned int levels_count;
> > -	unsigned int num_steps;
> > +	unsigned int num_steps = 0;
> 
> This can go. If we check the return code them this variable is no
> longer
> used uninitialized [I'm OK to make the change though... since you've
> kept my name at the top ;-) ].

Yes, I confirm that this works for me. Are you gona send a proper patch
out or should I do it?

> Daniel.
> 
> >  	struct property *prop;
> >  	unsigned int *table;
> >  	int length;
> > @@ -299,15 +299,13 @@ static int pwm_backlight_parse_dt(struct
> > device
> > *dev,
> >  		 * interpolation between each of the values of
> > brightness levels
> >  		 * and creates a new pre-computed table.
> >  		 */
> > -		of_property_read_u32(node, "num-interpolated-
> > steps",
> > -				     &num_steps);
> > -
> > -		/*
> > -		 * Make sure that there is at least two entries in
> > the
> > -		 * brightness-levels table, otherwise we can't
> > interpolate
> > -		 * between two points.
> > -		 */
> > -		if (num_steps) {
> > +		if ((of_property_read_u32(node, "num-interpolated-
> > steps",
> > +					  &num_steps) == 0) &&
> > (num_steps)) {
> > +			/*
> > +			 * Make sure that there is at least two
> > entries in the
> > +			 * brightness-levels table, otherwise we
> > can't
> > interpolate
> > +			 * between two points.
> > +			 */
> >  			if (data->max_brightness < 2) {
> >  				dev_err(dev, "can't
> > interpolate\n");
> >  				return -EINVAL;
> > -- 
> > 2.14.4