drm/edid: add separate drm_edid_connector_add_modes()

The original goal with drm_edid_connector_update() was to have a single
call for updating the connector and adding probed modes, in this order,
but that turned out to be problematic. Drivers that need to update the
connector in the .detect() callback would end up updating the probed
modes as well. Turns out the callback may be called so many times that
the probed mode list fills up without bounds, and this is amplified by
add_alternate_cea_modes() duplicating the CEA modes on every call,
actually running out of memory on some machines.

Kudos to Imre Deak <imre.deak@intel.com> for explaining this to me.

Go back to having separate drm_edid_connector_update() and
drm_edid_connector_add_modes() calls. The former may be called from
.detect(), .force(), or .get_modes(), but the latter only from
.get_modes().

Unlike drm_add_edid_modes(), have drm_edid_connector_add_modes() update
the probed modes from the EDID property instead of the passed in
EDID. This is mainly to enforce two things:

1) drm_edid_connector_update() must be called before
   drm_edid_connector_add_modes().

   Display info and quirks are needed for parsing the modes, and we
   don't want to call update_display_info() again to ensure the info is
   available, like drm_add_edid_modes() does.

2) The same EDID is used for both updating the connector and adding the
   probed modes.

Fortunately, the change is easy, because no driver has actually adopted
drm_edid_connector_update(). Not even i915, and that's mainly because of
the problem described above.

Cc: Imre Deak <imre.deak@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/e86fff1579f14ebf6334692526c8f6831cd02cac.1674144945.git.jani.nikula@intel.com

1 files changed, 2 insertions, 0 deletions

diff --git a/include/drm/drm_edid.h b/include/drm/drm_edid.h
index 372963600f1d..70ae6c290bdc 100644
--- a/include/drm/drm_edid.h
+++ b/include/drm/drm_edid.h
@@ -609,6 +609,8 @@ const struct drm_edid *drm_edid_read_custom(struct drm_connector *connector,
 					    void *context);
 int drm_edid_connector_update(struct drm_connector *connector,
 			      const struct drm_edid *edid);
+int drm_edid_connector_add_modes(struct drm_connector *connector);
+
 const u8 *drm_find_edid_extension(const struct drm_edid *drm_edid,
 				  int ext_id, int *ext_index);