| Message ID | 1537866837-4408-3-git-send-email-dkos@cadence.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | None | expand |
Hi Damian, Am Dienstag, 25. September 2018, 11:13:32 CEST schrieb Damian Kos: > From: Quentin Schulz <quentin.schulz@free-electrons.com> > > DP 1.4 introduced a DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT bit in > DP_TRAINING_AUX_RD_INTERVAL register. If set, DPCD registers from > DP_DPCD_REV to DP_ADAPTER_CAP should be retrieved starting from > DP_DPCD_REV_EXTENDED. All registers are copied except DP_DPCD_REV, > DP_MAX_LINK_RATE and DP_DOWNSTREAMPORT_PRESENT which represent the > "true capabilities" of DPRX device. > > Original DP_DPCD_REV, DP_MAX_LINK_RATE and DP_DOWNSTREAMPORT_PRESENT > might falsely return lower capabilities to "avoid interoperability > issues with some of the existing DP Source devices that malfunction > when they discover the higher capabilities within those three > registers.". > > Before DP 1.4, DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT bit was reserved > and read 0 so it's safe to check against it even if DP revision is > <1.4 > > Signed-off-by: Quentin Schulz <quentin.schulz@free-electrons.com> > Signed-off-by: Damian Kos <dkos@cadence.com> in v4 you received a Reviewed-by: Manasi Navare <manasi.d.navare@intel.com> for this patch. If a patch is largely unchanged from one version to another please add these previously received tags to the commit message. This prevents people from reviewing needlessly stuff twice ;-) . So the above should read ----- 8< ----- Signed-off-by: Quentin Schulz <quentin.schulz@free-electrons.com> Signed-off-by: Damian Kos <dkos@cadence.com> Reviewed-by: Manasi Navare <manasi.d.navare@intel.com> ----- 8< ----- Heiko
diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c index 8c6b9fd89f8a..735ebde5c2f0 100644 --- a/drivers/gpu/drm/drm_dp_helper.c +++ b/drivers/gpu/drm/drm_dp_helper.c @@ -370,10 +370,38 @@ int drm_dp_link_probe(struct drm_dp_aux *aux, struct drm_dp_link *link) { u8 values[3]; int err; + unsigned int addr; memset(link, 0, sizeof(*link)); - err = drm_dp_dpcd_read(aux, DP_DPCD_REV, values, sizeof(values)); + /* + * DP 1.4 introduced a DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT bit in + * DP_TRAINING_AUX_RD_INTERVAL register. If set, DPCD registers from + * DP_DPCD_REV to DP_ADAPTER_CAP should be retrieved starting from + * DP_DPCD_REV_EXTENDED. All registers are copied except DP_DPCD_REV, + * DP_MAX_LINK_RATE and DP_DOWNSTREAMPORT_PRESENT which represent the + * "true capabilities" of DPRX device. + * + * Original DP_DPCD_REV, DP_MAX_LINK_RATE and DP_DOWNSTREAMPORT_PRESENT + * might falsely return lower capabilities to "avoid interoperability + * issues with some of the existing DP Source devices that malfunction + * when they discover the higher capabilities within those three + * registers.". + * + * Before DP 1.4, DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT bit was reserved + * and read 0 so it's safe to check against it even if DP revision is + * <1.4 + */ + err = drm_dp_dpcd_readb(aux, DP_TRAINING_AUX_RD_INTERVAL, values); + if (err < 0) + return err; + + if (values[0] & DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT) + addr = DP_DP13_DPCD_REV; + else + addr = DP_DPCD_REV; + + err = drm_dp_dpcd_read(aux, addr, values, sizeof(values)); if (err < 0) return err;