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    SubjectRe: [PATCH 02/11 v3] drm/i915/intel_i2c: assign HDMI port D to pin pair 6
    On Mon, Mar 26, 2012 at 04:47:11PM +0200, Daniel Vetter wrote:
    > On Mon, Mar 26, 2012 at 10:26:41PM +0800, Daniel Kurtz wrote:
    > > According to i915 documentation [1], "Port D" (DP/HDMI Port D) is
    > > actually gmbus pin pair 6 (gmbus0.2:0 == 110b GPIOF), not 7 (111b).
    > > Pin pair 7 is a reserved pair.
    > >
    > > [1] Documentation for [DevSNB+] and [DevIBX], as found on
    > > http://intellinuxgraphics.org
    > >
    > > Note: the "reserved" and "disabled" pairs do not actually map to a
    > > physical pair of pins, nor GPIO regs and shouldn't be initialized or used.
    > > Fixing this is left for a later patch.
    > >
    > > This bug has not been noticed for two reasons:
    > > 1) "gmbus" mode is currently disabled - all transfers are actually using
    > > "bit-bang" mode which uses the GPIO port 5 (the "HDMI/DPD CTLDATA/CLK"
    > > pair), at register 0x5024 (defined as GPIOF i915_reg.h).
    > > Since this is the correct pair of pins for HDMI1, transfers succeed.
    >
    > ... this is no longer true on drm-intel-next.
    >
    > > 2) Even if gmbus mode is re-enabled, the first attempted transaction
    > > will fail because it tries to use the wrong ("Reserved") pin pair.
    > > However, the driver immediately falls back again to the bit-bang
    > > method, which correctly uses GPIOF, so again, transfers succeed.
    > >
    > > However, if gmbus mode is re-enabled and the GPIO fall-back mode is
    > > disabled, then reading an attached monitor's EDID fail.
    > >
    > > Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
    >
    > Otherwise this looks ok to me - I've checked with gen3 Bspec and we seem
    > to indeed have a 1:1 mapping, see "Display Registers", 1.5.3 "GPIO Control
    > Registers", the list right below the heading.

    well, scrap that, I've confused myself here a bit. Afaict we don't
    actually use these gmbus ports on earlier chips.
    >
    > Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
    >
    > When resending, can you please add the Bspec reference above?

    Can you you instead add a clear reference (Volume, Full Section plus
    Heading Title) for the Snb/Ibx public Bspec.

    Thanks, Daneil
    --
    Daniel Vetter
    Mail: daniel@ffwll.ch
    Mobile: +41 (0)79 365 57 48


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