On Thu, Feb 13, 2025 at 01:56:12AM +0200, Ville Syrjälä wrote: > On Thu, Jan 23, 2025 at 01:05:47PM +0200, Dmitry Baryshkov wrote: > > On Thu, Jan 23, 2025 at 12:05:29PM +0200, Jani Nikula wrote: > > > On Fri, 17 Jan 2025, Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx> wrote: > > > > Switch drm_dp_aux_dev.c to use new set of DPCD read / write helpers. > > > > > > This might be one of the few places where the old functions and the old > > > return value was used in a sensible manner. > > > > Well... Yes and no. What does it mean if we return less bytes? Is that > > still a protocol error? > > AFAIK short AUX replies are perfectly legal accoding to the DP > spec, but we've not really seen them happening in any real > use cases I suppose (although I'm not sure we have sufficient > logging to tell whether something failed completely or only > partially), hence why we've never really handled them > correctly. > > For aux_dev it might matter more because the common use > case is to just dump the entire DPCD, and some displays > violate the spec by having black holes inside the DPCD. > What I don't rembmer is whether those black holes actually > result in short replies, or whether the entire AUX transfer > gets rejected when it hits one even partially. I see. Let's keep the old interface just for the dp-aux-dev and make everybody else switch to the new interface. This might complicate the patchset a bit, but it seems that's how it should be done. > > The other concern with not handling short replies correctly > is that writes (and even some reads) can have side effects. > So when a short reply arrives we may have already triggered > some side effects while still claiming that the access > completely failed. > > I suppose if someone was sufficiently motivated they could > try to handle short replies more correctly and keep retrying > the remaining bytes (assuming that is the correct way to > handle them). Although with those black holes I guess > you'd eventually have to give up anyway before having > transferred all the bytes. -- With best wishes Dmitry
