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It is expected to be connecting at UHBR link rate, but we are observing HBR3 instead. Thanks, George cc: Mark.Broadworth@amd.com On 6/30/26 10:59, Jackie Dong wrote: > [WHY] > In the evolution of displays from DP 1.4 to DP 2.0, due to considerations > some factors,such as cost, some displays support 128b/132b encoding but > do not support UHBR rate transmission. The values can be read from DPCD > register address as below. > > 0x00006 is 03 > 0x02215 is 00 > > For such displays, the current kernel reports the following error message. > > [drm:dp_retrieve_lttpr_cap [amdgpu]] *ERROR* retrieve_link_cap: Invalid RX > 128b_132b_supported_link_rates > > [HOW] > Add new judgment: if all bits in dp_128b_132b_supported_link_rates.raw > are non-zero, then further determine the specific UHBR type; otherwise, > determine that the display does not support UHBR. > > Signed-off-by: Jackie Dong > --- > .../gpu/drm/amd/display/dc/link/protocols/link_dp_capability.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_capability.c b/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_capability.c > index 47abb4066709..58cbb7ac8f9e 100644 > --- a/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_capability.c > +++ b/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_capability.c > @@ -2079,7 +2079,8 @@ static bool retrieve_link_cap(struct dc_link *link) > if (!dpcd_read_sink_ext_caps(link)) > link->dpcd_sink_ext_caps.raw = 0; > > - if (link->dpcd_caps.channel_coding_cap.bits.DP_128b_132b_SUPPORTED) { > + if (link->dpcd_caps.channel_coding_cap.bits.DP_128b_132b_SUPPORTED && > + link->dpcd_caps.dp_128b_132b_supported_link_rates.raw) { > DC_LOG_DP2("128b/132b encoding is supported at link %d", link->link_index); > > /* Read 128b/132b suppoerted link rates */