[Intel-gfx] [PATCH 2/3] drm/i915: Reinitialize sink scrambling/TMDS clock ratio on HPD

[Ville Syrjälä]

On Thu, Dec 28, 2017 at 08:32:05PM +0530, Sharma, Shashank wrote:
> 
> 
> On 12/22/2017 11:58 PM, Ville Syrjala wrote:
> > From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> >
> > The LG 4k TV I have doesn't deassert HPD when I turn the TV off, but
> > when I turn it back on it will pulse the HPD line. By that time it has
> > forgotten everything we told it about scrambling and the clock ratio.
> > Hence if we want to get a picture out if it again we have to tell it
> > whether we're currently sending scrambled data or not. Implement
> > that via the encoder->post_hotplug() hook.
> I am not sure if I understood the problem statement correctly. Even if 
> the TV triggers HPD line while turning it back, I would expect:
> - EDID read for TV's detection, which will refresh SCDC and scrambling 
> capabilities
> - A new modeset will be triggered, which will program the scrambling and 
> high tmds clock ratio again
> - Once HDMI controller is programmed, it will generate scrambled signals 
> till next modeset / disable.
> 
> So why do we need to do this ? I might be missing something, but lets 
> discus about it.

The EDID is readable even when the HPD gets deasserted for a short
perios, hence we never consider the sink as being disconnected. Hence
there will be no modeset triggered by userspace.

-- 
Ville Syrjälä
Intel OTC