Messages in this thread | | | Date | Thu, 19 Sep 2013 09:13:11 -0700 | From | Mike Dunn <> | Subject | Re: [PATCH] pwm-backlight: allow for non-increasing brightness levels |
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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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