Hi Manasi, On Fri, Sep 21, 2018 at 12:59:30AM -0700, Manasi Navare wrote: > 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/ > If I'm not mistaken, you could get rid of the patch in the Intel driver when we have this one merged. Is there any reason not to, have I missed something? Thanks, Quentin > 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
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