[Intel-gfx] [PATCH] drm/i915: Check live status before reading edid

[Jindal, Sonika]

+Shashank

Shashank was planning to give a patch to bypass live status checks for older platforms.

Regards,
Sonika

-----Original Message-----
From: Chris Wilson [mailto:chris at chris-wilson.co.uk] 
Sent: Wednesday, March 9, 2016 2:34 AM
To: Jindal, Sonika <sonika.jindal at intel.com>
Cc: intel-gfx at lists.freedesktop.org
Subject: Re: [Intel-gfx] [PATCH] drm/i915: Check live status before reading edid

On Tue, Sep 15, 2015 at 09:44:20AM +0530, Sonika Jindal wrote:
> The Bspec is very clear that Live status must be checked about before 
> trying to read EDID over DDC channel. This patch makes sure that HDMI 
> EDID is read only when live status is up.
> 
> The live status doesn't seem to perform very consistent across various 
> platforms when tested with different monitors. The reason behind that 
> is some monitors are late to provide right voltage to set live_status up.
> So, after getting the interrupt, for a small duration, live status reg 
> fluctuates, and then settles down showing the correct staus.
> 
> This is explained here in, in a rough way:
> HPD line  ________________
> 			 |\ T1 = Monitor Hotplug causing IRQ
> 			 | \______________________________________
> 			 | |
>                          | |
> 			 | |   T2 = Live status is stable
> 			 | |  _____________________________________
> 			 | | /|
> Live status _____________|_|/ |
> 			 | |  |
> 			 | |  |
> 			 | |  |
> 			T0 T1  T2
> 
> (Between T1 and T2 Live status fluctuates or can be even low, 
> depending on  the monitor)
> 
> After several experiments, we have concluded that a max delay of 30ms 
> is enough to allow the live status to settle down with most of the 
> monitors. This total delay of 30ms has been split into a resolution of 
> 3 retries of 10ms each, for the better cases.
> 
> This delay is kept at 30ms, keeping in consideration that, HDCP 
> compliance expect the HPD handler to respond a plug out in 100ms, by disabling port.

This is a regression-fest. Revert with stable@?
-Chris

--
Chris Wilson, Intel Open Source Technology Centre