| Message ID | 20220831221321.748264-1-Jerry.Zuo@amd.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | drm/dp: Avoid Reading DPCD_REV Before Native Aux Read | expand |
Reviewed-by: Lyude Paul <lyude@redhat.com> On Wed, 2022-08-31 at 18:13 -0400, Fangzhi Zuo wrote: > The attempt to read DPCD_REV before any native aux read breaks > majority of DP2 compliance. > > The spec. requires DP_SINK_STATUS to be polled for the reset status > DP_INTRA_HOP_AUX_REPLY_INDICATION during the clear training stage. > > Polling DP_SINK_STATUS each time gets DPCD_REV read first > that makes non link training regsiter DPCD_REV get read > during UHBR link training. It violates DP2 compliance. > > Cc: Ville Syrjala <ville.syrjala@linux.intel.com> > Cc: Lyude Paul <lyude@redhat.com> > Signed-off-by: Fangzhi Zuo <Jerry.Zuo@amd.com> > --- > drivers/gpu/drm/display/drm_dp_helper.c | 18 ------------------ > 1 file changed, 18 deletions(-) > > diff --git a/drivers/gpu/drm/display/drm_dp_helper.c b/drivers/gpu/drm/display/drm_dp_helper.c > index e7c22c2ca90c..c7aa5bafa667 100644 > --- a/drivers/gpu/drm/display/drm_dp_helper.c > +++ b/drivers/gpu/drm/display/drm_dp_helper.c > @@ -571,24 +571,6 @@ ssize_t drm_dp_dpcd_read(struct drm_dp_aux *aux, unsigned int offset, > { > int ret; > > - /* > - * HP ZR24w corrupts the first DPCD access after entering power save > - * mode. Eg. on a read, the entire buffer will be filled with the same > - * byte. Do a throw away read to avoid corrupting anything we care > - * about. Afterwards things will work correctly until the monitor > - * gets woken up and subsequently re-enters power save mode. > - * > - * The user pressing any button on the monitor is enough to wake it > - * up, so there is no particularly good place to do the workaround. > - * We just have to do it before any DPCD access and hope that the > - * monitor doesn't power down exactly after the throw away read. > - */ > - if (!aux->is_remote) { > - ret = drm_dp_dpcd_probe(aux, DP_DPCD_REV); > - if (ret < 0) > - return ret; > - } > - > if (aux->is_remote) > ret = drm_dp_mst_dpcd_read(aux, offset, buffer, size); > else
diff --git a/drivers/gpu/drm/display/drm_dp_helper.c b/drivers/gpu/drm/display/drm_dp_helper.c index e7c22c2ca90c..c7aa5bafa667 100644 --- a/drivers/gpu/drm/display/drm_dp_helper.c +++ b/drivers/gpu/drm/display/drm_dp_helper.c @@ -571,24 +571,6 @@ ssize_t drm_dp_dpcd_read(struct drm_dp_aux *aux, unsigned int offset, { int ret; - /* - * HP ZR24w corrupts the first DPCD access after entering power save - * mode. Eg. on a read, the entire buffer will be filled with the same - * byte. Do a throw away read to avoid corrupting anything we care - * about. Afterwards things will work correctly until the monitor - * gets woken up and subsequently re-enters power save mode. - * - * The user pressing any button on the monitor is enough to wake it - * up, so there is no particularly good place to do the workaround. - * We just have to do it before any DPCD access and hope that the - * monitor doesn't power down exactly after the throw away read. - */ - if (!aux->is_remote) { - ret = drm_dp_dpcd_probe(aux, DP_DPCD_REV); - if (ret < 0) - return ret; - } - if (aux->is_remote) ret = drm_dp_mst_dpcd_read(aux, offset, buffer, size); else
The attempt to read DPCD_REV before any native aux read breaks majority of DP2 compliance. The spec. requires DP_SINK_STATUS to be polled for the reset status DP_INTRA_HOP_AUX_REPLY_INDICATION during the clear training stage. Polling DP_SINK_STATUS each time gets DPCD_REV read first that makes non link training regsiter DPCD_REV get read during UHBR link training. It violates DP2 compliance. Cc: Ville Syrjala <ville.syrjala@linux.intel.com> Cc: Lyude Paul <lyude@redhat.com> Signed-off-by: Fangzhi Zuo <Jerry.Zuo@amd.com> --- drivers/gpu/drm/display/drm_dp_helper.c | 18 ------------------ 1 file changed, 18 deletions(-)