[PATCH 2/2] drm/edid: Have cea_db_offsets() zero start/end when the data block collection isn't found

[Ville Syrjälä]

On Tue, Sep 10, 2019 at 11:46:20AM +0200, Jean Delvare wrote:
> Hi Ville,
> 
> On Mon,  2 Sep 2019 16:15:46 +0300, Ville Syrjala wrote:
> > From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > 
> > Let's make cea_db_offsets() a bit more convenient to use by
> > setting the start/end offsets to zero whenever the data block
> > collection isn't present. This makes it safe for the caller
> > to blindly iterate the data blocks even if there are none.
> > 
> > Cc: Jean Delvare <jdelvare at suse.de>
> > Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > ---
> >  drivers/gpu/drm/drm_edid.c | 8 ++++----
> >  1 file changed, 4 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> > index 7b3072fc550b..e5905dc764c1 100644
> > --- a/drivers/gpu/drm/drm_edid.c
> > +++ b/drivers/gpu/drm/drm_edid.c
> > @@ -3690,6 +3690,9 @@ cea_revision(const u8 *cea)
> >  static int
> >  cea_db_offsets(const u8 *cea, int *start, int *end)
> >  {
> > +	*start = 0;
> > +	*end = 0;
> > +
> >  	if (cea_revision(cea) < 3)
> >  		return -ENOTSUPP;
> >  
> > @@ -4116,10 +4119,7 @@ static void drm_edid_to_eld(struct drm_connector *connector, struct edid *edid)
> >  	if (cea_revision(cea) >= 3) {
> >  		int i, start, end;
> >  
> > -		if (cea_db_offsets(cea, &start, &end)) {
> > -			start = 0;
> > -			end = 0;
> > -		}
> > +		cea_db_offsets(cea, &start, &end);
> >  
> >  		for_each_cea_db(cea, i, start, end) {
> >  			db = &cea[i];
> 
> Not sure if that's really needed. As it stands there's only one
> function which wants to continue after cea_db_offsets() fails, all
> others just bail out at that point. Now that cea_db_offsets() checks
> for revision >= 3, the construct above could simply become:
> 
> 	int i, start, end;
> 
> 	if (cea_db_offsets(cea, &start, &end) == 0) {
> 		for_each_cea_db(cea, i, start, end) {
> 			db = &cea[i];
> 
> which is IMHO more elegant and does not require zeroing start and end
> in cea_db_offsets().

I dislike indentation. Also could perhaps even move the cea_db_offsets()
into the for_each_cea_db() macro so that the caller doesn't have to care
about these mundane details at all.

-- 
Ville Syrjälä
Intel