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

From: Marcel Ziswiler
Date: Sun Jul 15 2018 - 10:27:03 EST

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?

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@xxxxxxxxxx>
> 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@xxxxxxxxxxx>
> Signed-off-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
> ---
> 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@xxxxxxxxxxx>
From: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
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@xxxxxxxxxxx>
Signed-off-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
Signed-off-by: Marcel Ziswiler <marcel.ziswiler@xxxxxxxxxxx>
---
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;
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