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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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