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

[Jean Delvare <jdelvare@suse.de>]

On Tue, 10 Sep 2019 12:48:42 +0300, Ville Syrjälä wrote:
> 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@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@suse.de>
> > > Signed-off-by: Ville Syrjälä <ville.syrjala@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.

It would be the same as currently, so it's not that bad. But well I'm
not maintaining that piece of code so it's not my call anyway.

> 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.

If the macro stays readable, why not.

-- 
Jean Delvare
SUSE L3 Support
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