On Mon, Jun 29, 2026 at 10:14:36PM +0800, Yongxing Mou wrote:
> From: Abhinav Kumar <[email protected]>
>
> If the DP controller is capable of supporting multiple streams
> then initialize the DP sink in MST mode by programming the DP_MSTM_CTRL
> DPCD register to enable MST mode.
>
> Signed-off-by: Abhinav Kumar <[email protected]>
> Signed-off-by: Yongxing Mou <[email protected]>
> ---
> drivers/gpu/drm/msm/dp/dp_display.c | 48
> +++++++++++++++++++++++++++++++------
> 1 file changed, 41 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/dp/dp_display.c
> b/drivers/gpu/drm/msm/dp/dp_display.c
> index 5786e598a406..c3be656f10ee 100644
> --- a/drivers/gpu/drm/msm/dp/dp_display.c
> +++ b/drivers/gpu/drm/msm/dp/dp_display.c
> @@ -14,6 +14,7 @@
> #include <linux/string_choices.h>
> #include <drm/display/drm_dp_aux_bus.h>
> #include <drm/display/drm_hdmi_audio_helper.h>
> +#include <drm/display/drm_dp_mst_helper.h>
> #include <drm/drm_edid.h>
>
> #include "msm_drv.h"
> @@ -270,6 +271,31 @@ static int msm_dp_display_lttpr_init(struct
> msm_dp_display_private *dp, u8 *dpcd
> return lttpr_count;
> }
>
> +static void msm_dp_display_mst_init(struct msm_dp_display_private *dp)
> +{
> + u8 old_mstm_ctrl;
> + struct msm_dp *msm_dp = &dp->msm_dp_display;
> + int ret;
> +
> + /* clear sink MST state */
> + drm_dp_dpcd_read_byte(dp->aux, DP_MSTM_CTRL, &old_mstm_ctrl);
> +
> + ret = drm_dp_dpcd_write_byte(dp->aux, DP_MSTM_CTRL, 0);
> + if (ret < 0) {
> + DRM_ERROR("failed to clear DP_MSTM_CTRL, ret=%d\n", ret);
> + return;
> + }
Is it not enough to write the new value? Please add a small comment,
why (reference DP standard in the commit message, please).
> +
> + ret = drm_dp_dpcd_write_byte(dp->aux, DP_MSTM_CTRL,
> + DP_MST_EN | DP_UP_REQ_EN |
> DP_UPSTREAM_IS_SRC);
> + if (ret < 0) {
> + DRM_ERROR("sink MST enablement failed\n");
> + return;
> + }
> +
> + msm_dp->mst_active = true;
> +}
> +
> static int msm_dp_display_process_hpd_high(struct msm_dp_display_private *dp)
> {
> struct drm_connector *connector = dp->msm_dp_display.connector;
> @@ -288,14 +314,19 @@ static int msm_dp_display_process_hpd_high(struct
> msm_dp_display_private *dp)
> if (rc)
> goto end;
>
> - drm_edid = drm_edid_read_ddc(connector, &dp->aux->ddc);
> - drm_edid_connector_update(connector, drm_edid);
> + if (!(dp->max_stream > 1) || !drm_dp_read_mst_cap(dp->aux,
> dp->panel->dpcd)) {
> + drm_edid = drm_edid_read_ddc(connector, &dp->aux->ddc);
> + drm_edid_connector_update(connector, drm_edid);
>
> - if (!drm_edid) {
> - DRM_ERROR("panel edid read failed\n");
> - /* check edid read fail is due to unplug */
> - if (!msm_dp_aux_is_link_connected(dp->aux))
> - return -ETIMEDOUT;
> + if (!drm_edid) {
> + DRM_ERROR("panel edid read failed\n");
> + /* check edid read fail is due to unplug */
> + if (!msm_dp_aux_is_link_connected(dp->aux))
> + return -ETIMEDOUT;
> + }
> +
> + if (rc)
> + goto end;
This also is going to break DP. If you are using dp->max_streams as a
determining factor, rearrange commits so that max_streams are parseed
and set only after the rest of the commits are in place (and the driver
is ready for DP MST).
> }
>
> msm_dp_link_process_request(dp->link);
> @@ -317,6 +348,9 @@ static int msm_dp_display_process_hpd_high(struct
> msm_dp_display_private *dp)
> */
> msm_dp_link_psm_config(dp->link, &dp->panel->link_info, false);
>
> + if (dp->max_stream > 1 && drm_dp_read_mst_cap(dp->aux, dp->panel->dpcd))
> + msm_dp_display_mst_init(dp);
> +
> msm_dp_link_reset_phy_params_vx_px(dp->link);
>
> end:
>
> --
> 2.43.0
>
--
With best wishes
Dmitry
