On Fri, Mar 10, 2023 at 07:48:04PM +0200, Ville Syrjälä wrote: > On Thu, Mar 09, 2023 at 04:30:27PM -0500, Hamza Mahfooz wrote: > > We should be checking if drm_dp_dpcd_read() returns the size that we are > > asking it to read instead of just checking if it is greater than zero. > > Also, we should WARN_ON() here since this condition is only ever met, if > > there is an issue worth investigating. So, compare the return value of > > drm_dp_dpcd_read() to size and WARN_ON() if they aren't equal. > > > > Signed-off-by: Hamza Mahfooz <hamza.mahfooz@xxxxxxx> > > --- > > drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c > > index 8d598b322e5b..ed2ed7b1d869 100644 > > --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c > > +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c > > @@ -511,8 +511,8 @@ bool dm_helpers_dp_read_dpcd( > > return false; > > } > > > > - return drm_dp_dpcd_read(&aconnector->dm_dp_aux.aux, address, > > - data, size) > 0; > > + return !WARN_ON(drm_dp_dpcd_read(&aconnector->dm_dp_aux.aux, address, > > + data, size) != size); > > Just FYI there are devices out there that violate the DP spec and reads > from specific DPCD registers simply fail instead of returning the > expected 0. And of course anyone can yank the cable anytime, so in fact pretty much any DPCD read can fail. -- Ville Syrjälä Intel
