Re: [PATCH 3/3] drm: handle override edid and firmware EDID at drm_do_get_edid() level

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

On Thu, Feb 16, 2017 at 07:54:00PM +0200, Jani Nikula wrote:
> On Thu, 16 Feb 2017, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> > On Thu, Feb 16, 2017 at 12:36:45PM +0200, Jani Nikula wrote:
> >> Handle debugfs override edid and firmware edid at the low level to
> >> transparently and completely replace the real edid. Previously, we
> >> practically only used the modes from the override EDID, and none of the
> >> other data. This also prevents actual EDID reads when the EDID is to be
> >> overridden, but retains the DDC probe.
> >
> > Hmm. Isn't that a bad thing? If someone has broken DDC on their cable or
> > somethign then the override EDID wouldn't be returned by drm_get_edid().
> 
> Isn't this in line with how this currently works?

Not really. If connector->force is used and an override EDID is
provided, then drm_get_edid() likely never gets called, and the modes
come directly from the overide EDID. With your change forcing the
connector state wouldn't because we still wouldn't get any modes
from the override EDID due to the DDC check.

I guess one way around this would be to skip the DDC check if the
connector state has been forced.

> 
> BR,
> Jani.
> 
> 
> >
> >> 
> >> FIXME: validate override edid, deduplicate firmware edid validation.
> >> 
> >> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> >> ---
> >>  drivers/gpu/drm/drm_edid.c         | 15 +++++++++++++++
> >>  drivers/gpu/drm/drm_probe_helper.c | 19 +------------------
> >>  2 files changed, 16 insertions(+), 18 deletions(-)
> >> 
> >> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> >> index 362036360724..054e2d74eafc 100644
> >> --- a/drivers/gpu/drm/drm_edid.c
> >> +++ b/drivers/gpu/drm/drm_edid.c
> >> @@ -1309,6 +1309,10 @@ static void connector_bad_edid(struct drm_connector *connector,
> >>   * level, drivers must make all reasonable efforts to expose it as an I2C
> >>   * adapter and use drm_get_edid() instead of abusing this function.
> >>   *
> >> + * The EDID may be overridden using debugfs override_edid or firmare EDID
> >> + * (drm_load_edid_firmware()), in this priority order. Having either of them
> >> + * bypasses actual EDID reads.
> >> + *
> >>   * Return: Pointer to valid EDID or NULL if we couldn't find any.
> >>   */
> >>  struct edid *drm_do_get_edid(struct drm_connector *connector,
> >> @@ -1318,6 +1322,17 @@ struct edid *drm_do_get_edid(struct drm_connector *connector,
> >>  {
> >>  	int i, j = 0, valid_extensions = 0;
> >>  	u8 *edid, *new;
> >> +	struct edid *override = NULL;
> >> +
> >> +	if (connector->override_edid)
> >> +		override = drm_edid_duplicate((const struct edid *)
> >> +					      connector->edid_blob_ptr->data);
> >> +
> >> +	if (!override)
> >> +		override = drm_load_edid_firmware(connector);
> >> +
> >> +	if (!IS_ERR_OR_NULL(override))
> >> +		return override;
> >>  
> >>  	if ((edid = kmalloc(EDID_LENGTH, GFP_KERNEL)) == NULL)
> >>  		return NULL;
> >> diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
> >> index 358957118ca9..871326cbc465 100644
> >> --- a/drivers/gpu/drm/drm_probe_helper.c
> >> +++ b/drivers/gpu/drm/drm_probe_helper.c
> >> @@ -199,8 +199,6 @@ drm_connector_detect(struct drm_connector *connector, bool force)
> >>   *    drm_mode_probed_add(). New modes start their life with status as OK.
> >>   *    Modes are added from a single source using the following priority order.
> >>   *
> >> - *    - debugfs 'override_edid' (used for testing only)
> >> - *    - firmware EDID (drm_load_edid_firmware())
> >>   *    - &drm_connector_helper_funcs.get_modes vfunc
> >>   *    - if the connector status is connector_status_connected, standard
> >>   *      VESA DMT modes up to 1024x768 are automatically added
> >> @@ -305,22 +303,7 @@ int drm_helper_probe_single_connector_modes(struct drm_connector *connector,
> >>  		goto prune;
> >>  	}
> >>  
> >> -	if (connector->override_edid) {
> >> -		struct edid *edid = (struct edid *) connector->edid_blob_ptr->data;
> >> -
> >> -		count = drm_add_edid_modes(connector, edid);
> >> -		drm_edid_to_eld(connector, edid);
> >> -	} else {
> >> -		struct edid *edid = drm_load_edid_firmware(connector);
> >> -		if (!IS_ERR_OR_NULL(edid)) {
> >> -			drm_mode_connector_update_edid_property(connector, edid);
> >> -			count = drm_add_edid_modes(connector, edid);
> >> -			drm_edid_to_eld(connector, edid);
> >> -			kfree(edid);
> >> -		}
> >> -		if (count == 0)
> >> -			count = (*connector_funcs->get_modes)(connector);
> >> -	}
> >> +	count = (*connector_funcs->get_modes)(connector);
> >>  
> >>  	if (count == 0 && connector->status == connector_status_connected)
> >>  		count = drm_add_modes_noedid(connector, 1024, 768);
> >> -- 
> >> 2.1.4
> 
> -- 
> Jani Nikula, Intel Open Source Technology Center

-- 
Ville Syrjälä
Intel OTC
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