On Mon, May 25, 2026 at 03:55:16PM +0300, Imre Deak wrote:
> The ASUS DC301 USB-C dock containing a Realtek MST branch device
> supports the DSC decompression functionality on each of the dock's
> downstream connectors, even though there is no discoverable peer-to-peer
> virtual device in the MST topology (which the DP Standard
> requires/suggests to control the DSC functionality on a per-DFP basis).
> Add the DP_DPCD_QUIRK_DSC_WITHOUT_VIRTUAL_DPCD quirk for this branch
> device as well to enable the DSC decompression functionality on all DFP
> connectors of the dock, similarly to how this is done for dock's
> containing older Synaptics branch devices.
>
> Cc: Lyude Paul <[email protected]>
> Reported-and-tested-by: Shawn C Lee <[email protected]>
> Signed-off-by: Imre Deak <[email protected]>
Thanks for the reviews, patch is pushed drm-misc-next.
> ---
> drivers/gpu/drm/display/drm_dp_helper.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/drivers/gpu/drm/display/drm_dp_helper.c
> b/drivers/gpu/drm/display/drm_dp_helper.c
> index a6067471dd563..9c31e14cc413b 100644
> --- a/drivers/gpu/drm/display/drm_dp_helper.c
> +++ b/drivers/gpu/drm/display/drm_dp_helper.c
> @@ -2546,6 +2546,8 @@ static const struct dpcd_quirk dpcd_quirk_list[] = {
> { OUI(0x00, 0x00, 0x00), DEVICE_ID('C', 'H', '7', '5', '1', '1'),
> false, BIT(DP_DPCD_QUIRK_NO_SINK_COUNT) },
> /* Synaptics DP1.4 MST hubs can support DSC without virtual DPCD */
> { OUI(0x90, 0xCC, 0x24), DEVICE_ID_ANY, true,
> BIT(DP_DPCD_QUIRK_DSC_WITHOUT_VIRTUAL_DPCD) },
> + /* Realtek DP1.4 MST hubs can support DSC without virtual DPCD */
> + { OUI(0x00, 0xe0, 0x4c), DEVICE_ID('D', 'p', '1', '.', '4', 0), true,
> BIT(DP_DPCD_QUIRK_DSC_WITHOUT_VIRTUAL_DPCD) },
> /* Synaptics DP1.4 MST hubs require DSC for some modes on which it
> applies HBLANK expansion. */
> { OUI(0x90, 0xCC, 0x24), DEVICE_ID_ANY, true,
> BIT(DP_DPCD_QUIRK_HBLANK_EXPANSION_REQUIRES_DSC) },
> /* MediaTek panels (at least in U3224KBA) require DSC for modes with a
> short HBLANK on UHBR links. */
> --
> 2.49.1
>
