[Intel-gfx] [PATCH 1/2] drm/edid: Add a EDID edp panel quirk for forcing max lane count

[Ville Syrjälä]

On Wed, Apr 03, 2019 at 11:37:21AM -0700, Manasi Navare wrote:
> On Wed, Apr 03, 2019 at 03:14:51PM +0300, Ville Syrjälä wrote:
> > On Tue, Apr 02, 2019 at 02:52:34PM -0700, Manasi Navare wrote:
> > > For certain eDP 1.4 panels, we need to use max lane count for the
> > > link training to succeed.
> > > 
> > > This patch adds a EDID quirk for such eDP panels using
> > > their vendor ID and product ID to force using max lane count in the driver.
> > 
> > Rather than opening the quirk can of worms I think we should consider
> > changing the retry loop to do something more sensible than what it's
> > doing now. The current behaviour of "start at optimal settings (which
> > can be either min lanes or min rate), and then reduce lanes/rate until
> > stuff works" overlooks several possible combinations. One possible
> > approach could be to start the retry loop with max lanes + max rate
> > after the optimal settings have failed. It probably won't give you
> > the best power consumption, but at least you get a picture on the
> > screen if even a single lane count + rate combo works.
> >
> 
> So you are saying that for eDP only we should modify the retry function to
> retry with max lanes and max rate so what we used to do earlier with < eDP 1.4?
> 
> Hmm I could try doing that, the only concern I have there is that certain eDP
> panels just need a retry at same parameters to work so for such panels
> where the lower values of link rate/lane count work with just an extra retry
> we would still be using max link rate /lane count now with this change.

If the panels are borked then I wouln't worry about it as long a picture
appaears on the screen. And if the extra training cycle is because of
some bug in our code then we should figure it out what that bug is.

> 
> Or are you suggesting doing the retry with same params for edp < 1.4 and for all
> edp 1.4 , we retry with , max link rate lane ocunt?

retrain_fail()
{
	if (!use_max_params) {
		use_max_params = true;
		rate = max;
		lanes = max;
	} else {
		reduce rate/lanes as usual
	}
}

compute_config()
{
	if (use_max_params) {
		limits.min = limits.max;
	}
	...
}

or something like that.

-- 
Ville Syrjälä
Intel