problem configuring backlight brightness levels in device tree

problem configuring backlight brightness levels in device tree

[iw3gtf]

Hi,

I was trying to configure a pwm backlight on an embedded arm board
and I think I've found a minor problem.

In the source file 'drivers/video/backlight-pwm.c', in the function pwm_backlight_parse_dt()
you set the number of brightness values to:

pwm_backlight->backlight.brightness_max = length / sizeof(u32);

and then loop through the array with:

for (i = 0; i <=  pwm_backlight->backlight.brightness_max; i++)

to find the max of the array.

I think the '<=' should be a '<' otherwise you access an uninitialized value
one past the end of the array; this actually does not directly crash barebox
but the whole brightness values are scaled wrong.

giorgio


Giorgio, iw3gtf@arcor.de

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problem configuring backlight brightness levels in device tree

[giorgio.nicole]

Hi,

I was trying to configure a pwm backlight on an embedded arm board
and I think I've found a minor problem.

In the source file 'drivers/video/backlight-pwm.c', in the function pwm_backlight_parse_dt()
you set the number of brightness values to:

pwm_backlight->backlight.brightness_max = length / sizeof(u32);

and then loop through the array with:

for (i = 0; i <=  pwm_backlight->backlight.brightness_max; i++)

to find the max of the array.

I think the '<=' should be a '<' otherwise you access an uninitialized value
one past the end of the array; this actually does not directly crash barebox
but the whole brightness values are scaled wrong.

giorgio

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barebox@lists.infradead.org
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Re: problem configuring backlight brightness levels in device tree

[Sascha Hauer]

On Mon, Jul 11, 2016 at 01:51:11PM +0200, giorgio.nicole@arcor.de wrote:
> Hi,
> 
> I was trying to configure a pwm backlight on an embedded arm board
> and I think I've found a minor problem.
> 
> In the source file 'drivers/video/backlight-pwm.c', in the function pwm_backlight_parse_dt()
> you set the number of brightness values to:
> 
> pwm_backlight->backlight.brightness_max = length / sizeof(u32);
> 
> and then loop through the array with:
> 
> for (i = 0; i <=  pwm_backlight->backlight.brightness_max; i++)
> 
> to find the max of the array.
> 
> I think the '<=' should be a '<' otherwise you access an uninitialized value
> one past the end of the array; this actually does not directly crash barebox
> but the whole brightness values are scaled wrong.

Yes, you're right. Can you send a patch for this?

Sascha

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