[Intel-gfx] [PATCH] drm/i915: Fix DDC bus selection for multifunction SDVO

[Zhenyu Wang]

On 2010.04.23 16:16:12 -0400, Adam Jackson wrote:
> Multifunction SDVO cards stopped working after 14571b4, and would report
> something that looked remarkably like an ADD2 SPD ROM instead of EDID.
> This appears to be because DDC bus selection was utterly horked by that
> commit; controlled_output was no longer always a single bit, so
> intel_sdvo_select_ddc_bus would pick bus 0, which is (unsurprisingly)
> the SPD ROM bus, not a DDC bus.
> 
> So, instead of that, let's just use the DDC bus the child device table
> tells us to use.  I'm guessing at the bitmask and shifting from VBIOS
> dumps, but it can't possibly be worse.
> 
> cf. https://bugzilla.redhat.com/584229
> 

I'm worried about anything depending on BIOS table info for everytime.
Or if we have a fallback to spec method way to validate if BIOS info
really makes sense? As intel_sdvo_select_ddc_bus follows spec to select
ddc bus switch, which in most case should be followed by SDVO chip too.

We should fix the DDC bus selection issue by check attached_output now
and after detection for getting back the real connected output type, instead
of fixed in init.

-- 
Open Source Technology Center, Intel ltd.

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