Re: [PATCH v4] drivers: i915: Default backlight PWM frequency

Matthew Garrett
2011-11-11T23:15:21Z

On Fri, Nov 11, 2011 at 02:17:20PM -0800, Olof Johansson wrote:
> On Fri, Nov 11, 2011 at 02:12:58PM -0800, Simon Que wrote:
> > If the firmware did not initialize the backlight PWM registers, set up a
> > default PWM frequency of 200 Hz. This is determined using the following
> > formula:
> >
> > freq = refclk / (128 * pwm_max)
> >
> > The PWM register allows the max PWM value to be set. So we want to use
> > the formula, where freq = 200:
> >
> > pwm_max = refclk / (128 * freq)
> >
> > This patch will, in the case of missing PWM register initialization
> > values, look for the reference clock frequency. Based on that, it sets
> > an appropriate max PWM value for a frequency of 200 Hz.
> >
> > If no refclk frequency is found, the max PWM will be zero, which results
> > in no change to the PWM registers.
> >
> > Signed-off-by: Simon Que <sque@chromium.org>
>
> Acked-by: Olof Johansson <olof@lixom.net>
>
> Looks much better. I'm OK with this solution. Matthew?

I'd still prefer this to come from the firmware in some way, but in the
absence of the awesome let's go with the good.

Acked-by: Matthew Garrett <mjg@redhat.com>

--
Matthew Garrett | mjg59@srcf.ucam.org