Re: [Intel-gfx] [PATCH 1/3] drm/edid: Allow looking for ext blocks starting from a specified index

["Souza, Jose" <jose.souza@intel.com>]

On Thu, 2020-07-02 at 17:40 +0300, Ville Syrjälä wrote:
> On Tue, Jun 30, 2020 at 11:42:36PM +0000, Souza, Jose wrote:
> > On Wed, 2020-05-27 at 16:03 +0300, Ville Syrjala wrote:
> > > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > 
> > > Apparently EDIDs with multiple DispID ext blocks is a thing, so prepare
> > > for iterating through multiple ext blocks of the same type by
> > > passing the starting ext block index to drm_find_edid_extension(). Well
> > > also have drm_find_edid_extension() update the index to point to the
> > > next ext block on success. Thus we should be able to call
> > > drm_find_edid_extension() in loop.
> > > 
> > > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > ---
> > >  drivers/gpu/drm/drm_edid.c | 30 +++++++++++++++++++++---------
> > >  1 file changed, 21 insertions(+), 9 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> > > index d8372d63851b..f2531d51dfa2 100644
> > > --- a/drivers/gpu/drm/drm_edid.c
> > > +++ b/drivers/gpu/drm/drm_edid.c
> > > @@ -3188,7 +3188,8 @@ add_detailed_modes(struct drm_connector *connector, struct edid *edid,
> > >  /*
> > >   * Search EDID for CEA extension block.
> > >   */
> > > -static u8 *drm_find_edid_extension(const struct edid *edid, int ext_id)
> > > +static u8 *drm_find_edid_extension(const struct edid *edid,
> > > +				   int ext_id, int *ext_index)
> > >  {
> > >  	u8 *edid_ext = NULL;
> > >  	int i;
> > > @@ -3198,23 +3199,26 @@ static u8 *drm_find_edid_extension(const struct edid *edid, int ext_id)
> > >  		return NULL;
> > >  
> > >  	/* Find CEA extension */
> > > -	for (i = 0; i < edid->extensions; i++) {
> > > +	for (i = *ext_index; i < edid->extensions; i++) {
> > >  		edid_ext = (u8 *)edid + EDID_LENGTH * (i + 1);
> > >  		if (edid_ext[0] == ext_id)
> > >  			break;
> > >  	}
> > >  
> > > -	if (i == edid->extensions)
> > > +	if (i >= edid->extensions)
> > >  		return NULL;
> > >  
> > > +	*ext_index = i + 1;
> > > +
> > >  	return edid_ext;
> > >  }
> > >  
> > 
> > I would add something like drm_find_edid_n_extension() with the implementation above and then implement drm_find_edid_extension() calling
> > drm_find_edid_n_extension() but it is just one caller that is not using ext_index so LGTM.
> > 
> > >  
> > >  static u8 *drm_find_displayid_extension(const struct edid *edid,
> > > -					int *length, int *idx)
> > > +					int *length, int *idx,
> > > +					int *ext_index)
> > >  {
> > > -	u8 *displayid = drm_find_edid_extension(edid, DISPLAYID_EXT);
> > > +	u8 *displayid = drm_find_edid_extension(edid, DISPLAYID_EXT, ext_index);
> > >  	struct displayid_hdr *base;
> > >  	int ret;
> > >  
> > > @@ -3241,14 +3245,18 @@ static u8 *drm_find_cea_extension(const struct edid *edid)
> > >  	struct displayid_block *block;
> > >  	u8 *cea;
> > >  	u8 *displayid;
> > > +	int ext_index;
> > >  
> > >  	/* Look for a top level CEA extension block */
> > > -	cea = drm_find_edid_extension(edid, CEA_EXT);
> > > +	ext_index = 0;
> > 
> > In 2 places ext_index is initialized in the variable declaration and in 2 other places is not, all of it could be done in the declaration
> 
> No, in this case we need to reset it back to 0 when the start looking
> for the DispID ext block (as opposed to the CEA ext block). So I figured
> it's cleaner if both initialize it to 0 the same way. All the other
> places need just the one initialization.
> 
> Eventually I think I'd like some kind of for_each_ext_block() to make
> this stuff less crap...

Okay makes sense.

Reviewed-by: José Roberto de Souza <jose.souza@intel.com>

> 
> > or if you
> > really want to leave the context close to the users, initialize it in the "for (;;)" in the next patch.
> > 
> > With the change above:
> > 
> > Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
> > 
> > > +	cea = drm_find_edid_extension(edid, CEA_EXT, &ext_index);
> > >  	if (cea)
> > >  		return cea;
> > >  
> > >  	/* CEA blocks can also be found embedded in a DisplayID block */
> > > -	displayid = drm_find_displayid_extension(edid, &length, &idx);
> > > +	ext_index = 0;
> > > +	displayid = drm_find_displayid_extension(edid, &length, &idx,
> > > +						 &ext_index);
> > >  	if (!displayid)
> > >  		return NULL;
> > >  
> > > @@ -5195,8 +5203,10 @@ static int add_displayid_detailed_modes(struct drm_connector *connector,
> > >  	int length, idx;
> > >  	struct displayid_block *block;
> > >  	int num_modes = 0;
> > > +	int ext_index = 0;
> > >  
> > > -	displayid = drm_find_displayid_extension(edid, &length, &idx);
> > > +	displayid = drm_find_displayid_extension(edid, &length, &idx,
> > > +						 &ext_index);
> > >  	if (!displayid)
> > >  		return 0;
> > >  
> > > @@ -5870,11 +5880,13 @@ void drm_update_tile_info(struct drm_connector *connector,
> > >  			  const struct edid *edid)
> > >  {
> > >  	const void *displayid = NULL;
> > > +	int ext_index = 0;
> > >  	int length, idx;
> > >  	int ret;
> > >  
> > >  	connector->has_tile = false;
> > > -	displayid = drm_find_displayid_extension(edid, &length, &idx);
> > > +	displayid = drm_find_displayid_extension(edid, &length, &idx,
> > > +						 &ext_index);
> > >  	if (!displayid) {
> > >  		/* drop reference to any tile group we had */
> > >  		goto out_drop_ref;
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