[PATCH 28/45] drm/msm/dp: add an API to initialize MST on sink side

[Dmitry Baryshkov]

On Thu, Dec 05, 2024 at 08:31:59PM -0800, Abhinav Kumar wrote:
> 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 <quic_abhinavk at quicinc.com>
> ---
>  drivers/gpu/drm/msm/dp/dp_display.c | 32 ++++++++++++++++++++++++++++++++
>  1 file changed, 32 insertions(+)
> 
> diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
> index e69cdfbbe10484e47475ef189849f8ff6628bd7a..033d238e956263c1212fce45aab01316ef341edb 100644
> --- a/drivers/gpu/drm/msm/dp/dp_display.c
> +++ b/drivers/gpu/drm/msm/dp/dp_display.c
> @@ -380,6 +380,35 @@ static int msm_dp_display_send_hpd_notification(struct msm_dp_display_private *d
>  	return 0;
>  }
>  
> +static void msm_dp_display_mst_init(struct msm_dp_display_private *dp)
> +{
> +	const unsigned long clear_mstm_ctrl_timeout_us = 100000;
> +	u8 old_mstm_ctrl;
> +	struct msm_dp *msm_dp = &dp->msm_dp_display;
> +	int ret;
> +
> +	/* clear sink mst state */
> +	drm_dp_dpcd_readb(dp->aux, DP_MSTM_CTRL, &old_mstm_ctrl);
> +	drm_dp_dpcd_writeb(dp->aux, DP_MSTM_CTRL, 0);
> +
> +	/* add extra delay if MST state is not cleared */
> +	if (old_mstm_ctrl) {
> +		drm_dbg_dp(dp->drm_dev, "MSTM_CTRL is not cleared, wait %luus\n",
> +			   clear_mstm_ctrl_timeout_us);

"is not cleared" usually means that we wrote 0 to it, but the value
still stays on. Please rephrase the message, drop wait time.

> +		usleep_range(clear_mstm_ctrl_timeout_us,
> +			     clear_mstm_ctrl_timeout_us + 1000);
> +	}
> +
> +	ret = drm_dp_dpcd_writeb(dp->aux, DP_MSTM_CTRL,
> +				 DP_MST_EN | DP_UP_REQ_EN | DP_UPSTREAM_IS_SRC);
> +	if (ret < 0) {

if (ret != 1) ?

> +		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;
> @@ -414,6 +443,9 @@ 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 > DEFAULT_STREAM_COUNT && msm_dp_panel_read_mst_cap(dp->panel))
> +		msm_dp_display_mst_init(dp);
> +
>  	msm_dp_link_reset_phy_params_vx_px(dp->link);
>  	rc = msm_dp_ctrl_on_link(dp->ctrl, dp_display->mst_active);
>  	if (rc) {
> 
> -- 
> 2.34.1
> 

-- 
With best wishes
Dmitry