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

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

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.

> 
> 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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