[v3] backlight: pwm_bl: Fix uninitialized variable

Message ID 20180724071223.18901-1-daniel.thompson@linaro.org
State Superseded
Headers show
Series
  • [v3] backlight: pwm_bl: Fix uninitialized variable
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Commit Message

Daniel Thompson July 24, 2018, 7:12 a.m.
Currently, if the DT does not define num-interpolated-steps then
num_steps is undefined and the interpolation code will deploy randomly.
Fix with a simple initialize to zero.

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>
Tested-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
---

Notes:
    v3:
     - Switch to the simplest fix and zero the uninitialized variable. git
       grep indicates that ~25% of calls to of_property_read_u32() use this
       pattern (pre-initialize optional properties with sane values and
       ignore the return code).
    
    v2:
     - Simplify SoB chain (with Marcel's permission)
     - Separate complex if statement and make other similar calls use same
       return code checking approach
     - Tidy up comment formatting and fix pre-existing grammar error

 drivers/video/backlight/pwm_bl.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

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2.17.1

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Comments

Doug Anderson July 24, 2018, 11:56 p.m. | #1
Hi,

On Tue, Jul 24, 2018 at 12:12 AM, Daniel Thompson
<daniel.thompson@linaro.org> wrote:
> Currently, if the DT does not define num-interpolated-steps then
> num_steps is undefined and the interpolation code will deploy randomly.
> Fix with a simple initialize to zero.
>
> Fixes: 573fe6d1c25c ("backlight: pwm_bl: Linear interpolation between
> brightness-levels")

I think it may be incorrect to word-wrap the Fixes line.  A quick grep
through the source code looks like others agree.

> Reported-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
> Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
> Tested-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
> ---
>
> Notes:
>     v3:
>      - Switch to the simplest fix and zero the uninitialized variable. git
>        grep indicates that ~25% of calls to of_property_read_u32() use this
>        pattern (pre-initialize optional properties with sane values and
>        ignore the return code).
>
>     v2:
>      - Simplify SoB chain (with Marcel's permission)
>      - Separate complex if statement and make other similar calls use same
>        return code checking approach
>      - Tidy up comment formatting and fix pre-existing grammar error
>
>  drivers/video/backlight/pwm_bl.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Other than the nit on the commit message, this simple fix seems sane.

Reviewed-by: Douglas Anderson <dianders@chromium.org>
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Lee Jones July 25, 2018, 5:22 a.m. | #2
On Tue, 24 Jul 2018, Daniel Thompson wrote:

> Currently, if the DT does not define num-interpolated-steps then
> num_steps is undefined and the interpolation code will deploy randomly.
> Fix with a simple initialize to zero.
> 
> 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>
> Tested-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
> ---
> 
> Notes:
>     v3:
>      - Switch to the simplest fix and zero the uninitialized variable. git
>        grep indicates that ~25% of calls to of_property_read_u32() use this
>        pattern (pre-initialize optional properties with sane values and
>        ignore the return code).
>     
>     v2:
>      - Simplify SoB chain (with Marcel's permission)
>      - Separate complex if statement and make other similar calls use same
>        return code checking approach
>      - Tidy up comment formatting and fix pre-existing grammar error
> 
>  drivers/video/backlight/pwm_bl.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Once the 'Fixes:' line has been repaired:

  Acked-by: Lee Jones <lee.jones@linaro.org>

Patch

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;