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Message-ID: <nmrzydtcn4d3imhanxbvrmydvavarckcck3we5phzimd7l332z@gqfencrtaksn>
Date: Sun, 8 Dec 2024 10:54:21 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Abhinav Kumar <quic_abhinavk@...cinc.com>
Cc: Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
Marijn Suijten <marijn.suijten@...ainline.org>, David Airlie <airlied@...il.com>,
Simona Vetter <simona@...ll.ch>, Stephen Boyd <swboyd@...omium.org>,
Chandan Uddaraju <chandanu@...eaurora.org>, Guenter Roeck <groeck@...omium.org>,
Kuogee Hsieh <quic_khsieh@...cinc.com>, Bjorn Andersson <andersson@...nel.org>,
Konrad Dybcio <konradybcio@...nel.org>, Rob Herring <robh@...nel.org>,
Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>,
Vara Reddy <quic_varar@...cinc.com>, Rob Clark <robdclark@...omium.org>,
Tanmay Shah <tanmay@...eaurora.org>, linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
Jessica Zhang <quic_jesszhan@...cinc.com>, Laurent Pinchart <laurent.pinchart@...asonboard.com>
Subject: Re: [PATCH 35/45] drm/msm/dp: add a mst session mutex to protect
bridge ops
On Thu, Dec 05, 2024 at 08:32:06PM -0800, Abhinav Kumar wrote:
> To protect against concurrent access of the dp mst bridges
> introduce a session mutex.
Why is it necessary? What kind of concurrent access is expected?
Why wasn't it introduced together with struct msm_dp_mst?
>
> Signed-off-by: Abhinav Kumar <quic_abhinavk@...cinc.com>
> ---
> drivers/gpu/drm/msm/dp/dp_mst_drm.c | 20 ++++++++++++++++++++
> drivers/gpu/drm/msm/dp/dp_mst_drm.h | 1 +
> 2 files changed, 21 insertions(+)
>
> diff --git a/drivers/gpu/drm/msm/dp/dp_mst_drm.c b/drivers/gpu/drm/msm/dp/dp_mst_drm.c
> index 15c61fd37c418889074222c0f576778adadf51c9..313eb63b9a35cbbb36db2d7d8f0a85e4441f2998 100644
> --- a/drivers/gpu/drm/msm/dp/dp_mst_drm.c
> +++ b/drivers/gpu/drm/msm/dp/dp_mst_drm.c
> @@ -344,6 +344,7 @@ static void msm_dp_mst_bridge_atomic_pre_enable(struct drm_bridge *drm_bridge,
> struct msm_dp_mst_bridge *bridge;
> struct msm_dp *dp;
> struct msm_dp_mst_bridge_state *msm_dp_bridge_state;
> + struct msm_dp_mst *dp_mst;
>
> if (!drm_bridge) {
> DRM_ERROR("Invalid params\n");
> @@ -353,6 +354,7 @@ static void msm_dp_mst_bridge_atomic_pre_enable(struct drm_bridge *drm_bridge,
> bridge = to_msm_dp_mst_bridge(drm_bridge);
> msm_dp_bridge_state = to_msm_dp_mst_bridge_state(bridge);
> dp = bridge->display;
> + dp_mst = dp->msm_dp_mst;
>
> /* to cover cases of bridge_disable/bridge_enable without modeset */
> bridge->connector = msm_dp_bridge_state->connector;
> @@ -363,12 +365,14 @@ static void msm_dp_mst_bridge_atomic_pre_enable(struct drm_bridge *drm_bridge,
> return;
> }
>
> + mutex_lock(&dp_mst->mst_lock);
> msm_dp_display_atomic_prepare(dp);
>
> rc = _msm_dp_mst_bridge_pre_enable_part1(bridge, old_bridge_state);
> if (rc) {
> DRM_ERROR("[%d] DP display pre-enable failed, rc=%d\n", bridge->id, rc);
> msm_dp_display_unprepare(dp);
> + mutex_unlock(&dp_mst->mst_lock);
> return;
> }
>
> @@ -381,6 +385,8 @@ static void msm_dp_mst_bridge_atomic_pre_enable(struct drm_bridge *drm_bridge,
> drm_mode_vrefresh(&bridge->drm_mode),
> bridge->vcpi, bridge->start_slot,
> bridge->start_slot + bridge->num_slots);
> +
> + mutex_unlock(&dp_mst->mst_lock);
> }
>
> static void msm_dp_mst_bridge_atomic_disable(struct drm_bridge *drm_bridge,
> @@ -388,6 +394,7 @@ static void msm_dp_mst_bridge_atomic_disable(struct drm_bridge *drm_bridge,
> {
> struct msm_dp_mst_bridge *bridge;
> struct msm_dp *dp;
> + struct msm_dp_mst *mst;
>
> if (!drm_bridge) {
> DRM_ERROR("Invalid params\n");
> @@ -401,6 +408,9 @@ static void msm_dp_mst_bridge_atomic_disable(struct drm_bridge *drm_bridge,
> }
>
> dp = bridge->display;
> + mst = dp->msm_dp_mst;
> +
> + mutex_lock(&mst->mst_lock);
>
> _msm_dp_mst_bridge_pre_disable_part1(bridge, old_bridge_state);
>
> @@ -410,6 +420,8 @@ static void msm_dp_mst_bridge_atomic_disable(struct drm_bridge *drm_bridge,
>
> drm_dbg_dp(dp->drm_dev, "mst bridge:%d conn:%d disable complete\n", bridge->id,
> DP_MST_CONN_ID(bridge));
> +
> + mutex_unlock(&mst->mst_lock);
> }
>
> static void msm_dp_mst_bridge_atomic_post_disable(struct drm_bridge *drm_bridge,
> @@ -418,6 +430,7 @@ static void msm_dp_mst_bridge_atomic_post_disable(struct drm_bridge *drm_bridge,
> int conn = 0;
> struct msm_dp_mst_bridge *bridge;
> struct msm_dp *dp;
> + struct msm_dp_mst *mst;
>
> if (!drm_bridge) {
> DRM_ERROR("Invalid params\n");
> @@ -433,6 +446,9 @@ static void msm_dp_mst_bridge_atomic_post_disable(struct drm_bridge *drm_bridge,
> conn = DP_MST_CONN_ID(bridge);
>
> dp = bridge->display;
> + mst = dp->msm_dp_mst;
> +
> + mutex_lock(&mst->mst_lock);
>
> msm_dp_display_atomic_post_disable_helper(dp, bridge->msm_dp_panel);
>
> @@ -444,6 +460,8 @@ static void msm_dp_mst_bridge_atomic_post_disable(struct drm_bridge *drm_bridge,
>
> drm_dbg_dp(dp->drm_dev, "mst bridge:%d conn:%d post disable complete\n",
> bridge->id, conn);
> +
> + mutex_unlock(&mst->mst_lock);
> }
>
> static void msm_dp_mst_bridge_mode_set(struct drm_bridge *drm_bridge,
> @@ -1072,6 +1090,8 @@ int msm_dp_mst_init(struct msm_dp *dp_display, u32 max_streams, u32 max_dpcd_tra
>
> dp_display->msm_dp_mst = msm_dp_mst;
>
> + mutex_init(&msm_dp_mst->mst_lock);
> +
> msm_dp_mst->mst_initialized = true;
>
> drm_dbg_dp(dp_display->drm_dev, "dp drm mst topology manager init completed\n");
> diff --git a/drivers/gpu/drm/msm/dp/dp_mst_drm.h b/drivers/gpu/drm/msm/dp/dp_mst_drm.h
> index 5fe5dc7596086467e9a3b3d7d04a665853fbb3d7..b1adb8a61115d4809107553809206bb2ed3c6c3d 100644
> --- a/drivers/gpu/drm/msm/dp/dp_mst_drm.h
> +++ b/drivers/gpu/drm/msm/dp/dp_mst_drm.h
> @@ -80,6 +80,7 @@ struct msm_dp_mst {
> struct drm_dp_aux *dp_aux;
> bool mst_session_hpd_state;
> u32 max_streams;
> + struct mutex mst_lock;
> };
>
> struct msm_dp_mst_connector {
>
> --
> 2.34.1
>
--
With best wishes
Dmitry
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