From: Olof Johansson <olof@lixom.net>
To: Simon Que <sque@chromium.org>
Cc: intel-gfx@lists.freedesktop.org, olofj@chromium.org, snanda@chromium.org
Subject: Re: [PATCH v4] drivers: i915: Default backlight PWM frequency
Date: Fri, 11 Nov 2011 14:17:20 -0800 [thread overview]
Message-ID: <20111111221720.GA30923@quad.lixom.net> (raw)
In-Reply-To: <1321049578-26742-1-git-send-email-sque@chromium.org>
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?
-Olof
next prev parent reply other threads:[~2011-11-11 22:17 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-11-11 22:12 [PATCH v4] drivers: i915: Default backlight PWM frequency Simon Que
2011-11-11 22:17 ` Olof Johansson [this message]
2011-11-11 22:30 ` Matthew Garrett
2011-11-15 18:47 ` Takashi Iwai
2012-01-17 10:34 ` Daniel Vetter
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