Re: [PATCH v3 17/38] drm/msm/dp: add support to send ACT packets for MST
From: Dmitry Baryshkov
Date: Wed Apr 01 2026 - 02:48:10 EST
On 01/04/2026 09:44, Yongxing Mou wrote:
On 8/26/2025 5:10 AM, Dmitry Baryshkov wrote:
On Mon, Aug 25, 2025 at 10:16:03PM +0800, Yongxing Mou wrote:In some cases, MST still works correctly even when the ACT trigger fails; here refer to the downstream implementation.
From: Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx>
Whenever virtual channel slot allocation changes, the DP
source must send the action control trigger sequence to notify
the sink about the same. This would be applicable during the
start and stop of the pixel stream. Add the infrastructure
to be able to send ACT packets for the DP controller when
operating in MST mode.
Signed-off-by: Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx>
Signed-off-by: Yongxing Mou <yongxing.mou@xxxxxxxxxxxxxxxx>
---
drivers/gpu/drm/msm/dp/dp_ctrl.c | 39 ++++++++++++++++++++++++++ +++++++++--
drivers/gpu/drm/msm/dp/dp_ctrl.h | 4 ++--
drivers/gpu/drm/msm/dp/dp_display.c | 3 ++-
drivers/gpu/drm/msm/dp/dp_display.h | 1 +
drivers/gpu/drm/msm/dp/dp_reg.h | 2 ++
5 files changed, 44 insertions(+), 5 deletions(-)
diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/ dp/dp_ctrl.c
index 608a1a077301b2ef3c77c271d873bb4364abe779..16e5ed58e791971d5dca3077cbb77bfcc186505a 100644
--- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
+++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
@@ -142,6 +142,7 @@ struct msm_dp_ctrl_private {
bool core_clks_on;
bool link_clks_on;
bool stream_clks_on[DP_STREAM_MAX];
+ bool mst_active;
};
static inline u32 msm_dp_read_ahb(const struct msm_dp_ctrl_private *ctrl, u32 offset)
@@ -227,6 +228,32 @@ static int msm_dp_aux_link_configure(struct drm_dp_aux *aux,
return 0;
}
+void msm_dp_ctrl_mst_send_act(struct msm_dp_ctrl *msm_dp_ctrl)
+{
+ struct msm_dp_ctrl_private *ctrl;
+ bool act_complete;
+
+ ctrl = container_of(msm_dp_ctrl, struct msm_dp_ctrl_private, msm_dp_ctrl);
+
+ if (!ctrl->mst_active)
+ return;
+
+ msm_dp_write_link(ctrl, REG_DP_MST_ACT, 0x1);
+ /* make sure ACT signal is performed */
+ wmb();
+
+ msleep(20); /* needs 1 frame time */
+
+ act_complete = msm_dp_read_link(ctrl, REG_DP_MST_ACT);
+
+ if (!act_complete)
+ drm_dbg_dp(ctrl->drm_dev, "mst ACT trigger complete SUCCESS\n");
+ else
+ drm_dbg_dp(ctrl->drm_dev, "mst ACT trigger complete failed\n");
Shouldn't it return an error if the register dind't latch? Also,
shouldn't we set mst_active only if the write went through?
I don't think it is a good idea. It would be better to signal this to the user and rollback the MST configuration (as in the case of any other error).
I will change my mind if you point out i915, amdgpu or nouveau drivers ignoring the ACT issues.
--
With best wishes
Dmitry