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    SubjectRe: [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 <>

    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
    Mobile: +41 (0)79 365 57 48

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      Last update: 2011-09-30 20:19    [W:0.022 / U:73.884 seconds]
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