linux-kernel - Re: [PATCH 14/21] drm/i915: Correct eDP panel power sequencing delay computations

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Date:	Fri, 30 Sep 2011 20:16:44 +0200
From:	Daniel Vetter <daniel@...ll.ch>
To:	Keith Packard <keithp@...thp.com>
Cc:	Dave Airlie <airlied@...hat.com>, intel-gfx@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH 14/21] drm/i915: Correct eDP panel power sequencing delay
 computations

On Thu, Sep 29, 2011 at 06:09:46PM -0700, Keith Packard wrote:
> Store the panel power sequencing delays in the dp private structure,
> rather than the global device structure. Who knows, maybe we'll get
> more than one eDP device in the future.
> 
> Look at both the current hardware register settings and the VBT
> specified panel power sequencing timings. Use the maximum of the two
> delays, to make sure things work reliably. If there is no VBT data,
> then those values will be initialized to zero, so we'll just use the
> values as programmed in the hardware.
> 
> This patch computes power-up and power-down delays, rather than using
> portions of the appropriate delay values as found in the hardware. The
> eDP specified delay between raising VCC and communicating over the aux
> channel includes both the power rise time (T1) and the aux channel
> communication delay (T3). The eDP specified delay between powering
> down the device and powering it back up includes both the power fall
> time (T11) and the device idle time (T12).
> 
> From the hardware, I'm taking the T3 value from the PP_OFF_DELAYS
> Power_Down_delay value, which is actually documented to be the 'T3
> time sequence' value used 'during power up'. There aren't separate T1
> and T2 values, but there is a combined T1+T2 value in the PP_ON_DELAYS
> register, so I use that instead.
> 
> VBT doesn't provide any values for T1 or T2, so we'll always just use
> the hardware value for that.
> 
> The panel power up delay is thus T1 + T2 + T3, which should be
> sufficient in all cases.
> 
> The panel power down delay is T1 + T2 + T12, using T1+T2 as a proxy
> for T11, which isn't available anywhere.
> 
> On the macbook air I'm testing with, this yields a power-up delay of
> over 200ms and a power-down delay of over 600ms. It all works now, but
> we're frobbing these power controls several times during mode setting,
> making the whole process take an awfully long time.
> 
> Signed-off-by: Keith Packard <keithp@...thp.com>

Awesome patch description and the code agrees with what I've cross-checked
on bspec. The only fear I have is that we currently ignore the backlight
on/off timings and some panel probably relies on use waiting for backlight
on/off + panel on/off in total. But that's material for another patch.

Reviewed-by: Daniel Vetter <daniel.vetter@...ll.ch>
-- 
Daniel Vetter
Mail: daniel@...ll.ch
Mobile: +41 (0)79 365 57 48
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