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 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.

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?

Manasi

> > 
> > Cc: Clint Taylor <Clinton.A.Taylor@intel.com>
> > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > Tested-by: Albert Astals Cid <aacid@kde.org>
> > Tested-by: Emanuele Panigati <ilpanich@gmail.com>
> > Tested-by: Ralgor <ralgorfdb@compuspex.org>
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=109959
> > Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
> > ---
> >  drivers/gpu/drm/drm_edid.c  | 10 ++++++++++
> >  include/drm/drm_connector.h |  5 +++++
> >  2 files changed, 15 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> > index 2c22ea446075..fbc661806484 100644
> > --- a/drivers/gpu/drm/drm_edid.c
> > +++ b/drivers/gpu/drm/drm_edid.c
> > @@ -82,6 +82,8 @@
> >  #define EDID_QUIRK_FORCE_10BPC			(1 << 11)
> >  /* Non desktop display (i.e. HMD) */
> >  #define EDID_QUIRK_NON_DESKTOP			(1 << 12)
> > +/* Force max lane count */
> > +#define EDID_QUIRK_FORCE_MAX_LANE_COUNT		(1 << 13)
> >  
> >  struct detailed_mode_closure {
> >  	struct drm_connector *connector;
> > @@ -189,6 +191,10 @@ static const struct edid_quirk {
> >  
> >  	/* OSVR HDK and HDK2 VR Headsets */
> >  	{ "SVR", 0x1019, EDID_QUIRK_NON_DESKTOP },
> > +
> > +	/* SHP eDP 1.4 panel only works with max lane count */
> > +	{ "SHP", 0x149a, EDID_QUIRK_FORCE_MAX_LANE_COUNT },
> > +	{ "SHP", 0x148e, EDID_QUIRK_FORCE_MAX_LANE_COUNT },
> >  };
> >  
> >  /*
> > @@ -4463,6 +4469,7 @@ drm_reset_display_info(struct drm_connector *connector)
> >  	memset(&info->hdmi, 0, sizeof(info->hdmi));
> >  
> >  	info->non_desktop = 0;
> > +	info->force_max_lane_count = 0;
> >  }
> >  
> >  u32 drm_add_display_info(struct drm_connector *connector, const struct edid *edid)
> > @@ -4744,6 +4751,9 @@ int drm_add_edid_modes(struct drm_connector *connector, struct edid *edid)
> >  	if (quirks & EDID_QUIRK_FORCE_12BPC)
> >  		connector->display_info.bpc = 12;
> >  
> > +	if (quirks & EDID_QUIRK_FORCE_MAX_LANE_COUNT)
> > +		connector->display_info.force_max_lane_count = true;
> > +
> >  	return num_modes;
> >  }
> >  EXPORT_SYMBOL(drm_add_edid_modes);
> > diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> > index 02a131202add..45436d40ffe3 100644
> > --- a/include/drm/drm_connector.h
> > +++ b/include/drm/drm_connector.h
> > @@ -457,6 +457,11 @@ struct drm_display_info {
> >  	 * @non_desktop: Non desktop display (HMD).
> >  	 */
> >  	bool non_desktop;
> > +
> > +	/**
> > +	 * @force_max_lane_count: Link training requires max lane count to pass
> > +	 */
> > +	bool force_max_lane_count;
> >  };
> >  
> >  int drm_display_info_set_bus_formats(struct drm_display_info *info,
> > -- 
> > 2.19.1
> 
> -- 
> Ville Syrjälä
> Intel
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