On 09/19/2013 04:56 AM, Thierry Reding wrote:
> On Thu, Sep 12, 2013 at 11:35:52AM -0700, Mike Dunn wrote:
>> Currently the driver assumes that the values specified in the
>> brightness-levels
>> device tree property increase as they are parsed from left to right. But
>> boards
>> that invert the signal between the PWM output and the backlight will need to
>> specify decreasing brightness-levels. This patch removes the assumption that
>> the last element of the array is the max value, and instead searches the
>> array
>> for the max value and uses that as the normalizing value when determining the
>> duty cycle.
>
> "maximum value", "... and uses that as the scale to normalize the duty
> cycle"?
It's been a while since my last math class... is "normalizing value" not the
correct term? Maybe just "uses that in the duty cycle calculation"?
>
> Also please wrap commit messages at 72 characters.
OK. Sorry, didn't know.
>
>> diff --git a/drivers/video/backlight/pwm_bl.c
>> b/drivers/video/backlight/pwm_bl.c
>> index 1fea627..d66aaa0 100644
>> --- a/drivers/video/backlight/pwm_bl.c
>> +++ b/drivers/video/backlight/pwm_bl.c
>> @@ -27,6 +27,7 @@ struct pwm_bl_data {
>> unsigned int period;
>> unsigned int lth_brightness;
>> unsigned int *levels;
>> + unsigned int max_level;
>
> Perhaps call this "scale"? Otherwise there some potential to mix it up
> with max_brightness.
Yes, this name is thorny. The code was somewhat confusing to me until I
realized that for the DT case, brightness and max_brightness are indices into
the levels[] array, whereas they are actual values for the platform_data case.
I'll go with "scale" if you prefer.
>
>> @@ -195,7 +196,15 @@ static int pwm_backlight_probe(struct platform_device
>> *pdev)
>> }
>>
>> if (data->levels) {
>> - max = data->levels[data->max_brightness];
>> + int i, max_value = 0, max_idx = 0;
>
> i should be unsigned int to match the type of data->max_brightness.
Yes, thanks. I'm surprised there's no warning from the compiler. I'm also
assigning an unsigned to a signed.
>
>> + for (i = 0; i <= data->max_brightness; i++) {
>
> There should be a blank line above this one to increase readability.
>
>> + if (data->levels[i] > max_value) {
>> + max_value = data->levels[i];
>> + max_idx = i;
>> + }
>> + }
>> + pb->max_level = max_idx;
>
> Some here.
>
> Also I suggest to just drop the max_ prefix from the local variables.
> Perhaps also simplify all of it to something like:
>
> for (i = 0; i <= data->max_brightness; i++)
> if (data->levels[i] > pb->scale)
> pb->scale = data->levels[i];
>
> And get rid of the index altogether. That way you can use pb->scale
> directly during the computation of the duty cycle and don't have to
> index the levels array over and over again.
Ok, if you prefer. The reason I made max_level an index is for consistency.
For the DT case, brightness and max_brightness are indices, and I had already
been confused by the value-versus-index issue.
Thanks much for the review! I'll ready a v2 patch.
Mike
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