[Intel-gfx] [PATCH 2/2] drm/i915: Support for HDMI complaince HPD

[Chris Wilson]

On Tue, Aug 12, 2014 at 06:08:21PM +0530, shashank.sharma at intel.com wrote:
> From: Shashank Sharma <shashank.sharma at intel.com>
> 
> During the HDMI complaince tests, most of the HDMI analyzers
> issue a soft HPD, to automate the tests. This process keeps
> the HDMI cable connected, and DDC chhanel alive.
> 
> HDMI detect() logic relies on EDID readability, to decide if
> its a HDMI connect or disconnect event. But in this case, the
> EDID is always readable, as HDMI cable is physically connected
> and DDC channel is UP, so detect() always reports a HDMI connect
> even if its intended to be a HDMI disconnect call.
> 
> So if HDMI compliance is enabled, we should rely on the live status
> register, than EDID availability. This patch adds:
> 1. One kernel command line parameter for i915 module, which indicates
>    if we want to support HDMI compliance, for this platform.

I would rather have this as an output property. In fact, I would like
the hotplug detection method exposed (and even selectable, but other
than this compliance testing, I can't think of a scenario where the
kernel shouldn't be able to figure things out for itself).

> 2. A new function to read EDID, which gets called only in case of
>    HDMI compliance support is required. This function reads EDID only
>    if live status register is up. The normal code flow doesn't get effected
>    if kernel command line parameter is not enabled.
> 3. After various experiments on VLV2 board, with various HDMI monitors
>    we have seen that, with few monitors, the live status register gets
>    set after a slight delay, and then stays reliably. To support such
>    monitors, there is a busy-loop added, with a max delay upto 50ms,
>    with a status check after every 10ms. Please see the comment in
>    intel_hdmi_get_edid.

Wouldn't a tidier solution be to delay the hpd by 50-100ms after the
hotplug interrupt? That may overcome the issue with the live status for
all connectors...
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre