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

[Manasi Navare <manasi.d.navare@intel.com>]

On Wed, Apr 03, 2019 at 09:55:56PM +0300, Ville Syrjälä wrote:
> 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.
>

But we should do this retrain() in our existing modeset_retry() and intel_dp_get_fallback_values()
and only do it for eDP right?
Because DP we have the retrain loops as per the compliance, if we change that that will
affect all the compliance tests.

Manasi
 
> > 
> > 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
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