[Intel-gfx] [PATCH 1/3] drm/i915: Try to use fast+narrow link on eDP again and fall back to the old max strategy on failure

[Ville Syrjälä]

On Thu, Mar 19, 2020 at 05:53:08PM +0100, Hans de Goede wrote:
> Hi,
> 
> On 3/19/20 5:38 PM, Ville Syrjala wrote:
> > From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > 
> > Some new eDP panels don't like to operate at the max parameters, and
> > instead we need to go for an optimal confiugration. That unfortunately
> > doesn't work with older eDP panels which are generally only guaranteed
> > to work at the max parameters.
> > 
> > To solve these two conflicting requirements let's start with the optimal
> > setup, and if that fails we start again with the max parameters. The
> > downside is probably an extra modeset when we switch strategies but
> > I don't see a good way to avoid that.
> > 
> > For a bit of history we first tried to go for the fast+narrow in
> > commit 7769db588384 ("drm/i915/dp: optimize eDP 1.4+ link config
> > fast and narrow"). but that had to be reverted due to regression
> > on older panels in commit f11cb1c19ad0 ("drm/i915/dp: revert back
> > to max link rate and lane count on eDP"). So now we try to get
> > the best of both worlds by using both strategies.
> > 
> > v2: Deal with output_bpp and uapi vs. hw state split
> >      Reword some comments
> 
> I'm wondering if, at least for the fastset case, but also
> for later modesets I guess, it would not be better to
> first check if the link is already setup (panel already on)
> and then check if the existing parameters match our min/max
> criteria and if they do continue with those settings?
> 
> Doing something like this would likely also fix:
> https://gitlab.freedesktop.org/drm/intel/issues/1476

Yeah, I've thought about doing that. It's a bit ugly though, and
probably requires some actual thought so that we don't end up
doing something stupid.

-- 
Ville Syrjälä
Intel