Thanks for the patch. Verified with the DP 1.4 spec and looks good to me. Also look at the related patch that makes use of the correct extended capabilities: https://patchwork.freedesktop.org/patch/249400/ Reviewed-by: Manasi Navare <manasi.d.navare@xxxxxxxxx> Manasi On Thu, Sep 20, 2018 at 03:54:37PM +0100, Damian Kos wrote: > From: Quentin Schulz <quentin.schulz@xxxxxxxxxxxxxxxxxx> > > 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@xxxxxxxxxxxxxxxxxx> > Signed-off-by: Damian Kos <dkos@xxxxxxxxxxx> > --- > drivers/gpu/drm/drm_dp_helper.c | 30 +++++++++++++++++++++++++++++- > 1 file changed, 29 insertions(+), 1 deletion(-) > > 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; > > -- > 2.17.1 > > _______________________________________________ > dri-devel mailing list > dri-devel@xxxxxxxxxxxxxxxxxxxxx > https://lists.freedesktop.org/mailman/listinfo/dri-devel
