Re: [Nouveau] [PATCH v2 19/27] drm/dp_mst: Handle UP requests asynchronously
On Tue, Sep 03, 2019 at 04:45:57PM -0400, Lyude Paul wrote:
> Once upon a time, hotplugging devices on MST branches actually worked in
> DRM. Now, it only works in amdgpu (likely because of how it's hotplug
> handlers are implemented). On both i915 and nouveau, hotplug
> notifications from MST branches are noticed - but trying to respond to
> them causes messaging timeouts and causes the whole topology state to go
> out of sync with reality, usually resulting in the user needing to
> replug the entire topology in hopes that it actually fixes things.
>
> The reason for this is because the way we currently handle UP requests
> in MST is completely bogus. drm_dp_mst_handle_up_req() is called from
> drm_dp_mst_hpd_irq(), which is usually called from the driver's hotplug
> handler. Because we handle sending the hotplug event from this function,
> we actually cause the driver's hotplug handler (and in turn, all
> sideband transactions) to block on
> drm_device->mode_config.connection_mutex. This makes it impossible to
> send any sideband messages from the driver's connector probing
> functions, resulting in the aforementioned sideband message timeout.
>
> There's even more problems with this beyond breaking hotplugging on MST
> branch devices. It also makes it almost impossible to protect
> drm_dp_mst_port struct members under a lock because we then have to
> worry about dealing with all of the lock dependency issues that ensue.
>
> So, let's finally actually fix this issue by handling the processing of
> up requests asyncronously. This way we can send sideband messages from
> most contexts without having to deal with getting blocked if we hold
> connection_mutex. This also fixes MST branch device hotplugging on i915,
> finally!
>
> Cc: Juston Li
> Cc: Imre Deak
> Cc: Ville Syrjälä
> Cc: Harry Wentland
> Cc: Daniel Vetter
> Signed-off-by: Lyude Paul
Looks really good!
Reviewed-by: Sean Paul
> ---
> drivers/gpu/drm/drm_dp_mst_topology.c | 146 +++---
> include/drm/drm_dp_mst_helper.h | 16 +++
> 2 files changed, 122 insertions(+), 40 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> b/drivers/gpu/drm/drm_dp_mst_topology.c
> index cfaf9eb7ace9..5101eeab4485 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -46,6 +46,12 @@
> * protocol. The helpers contain a topology manager and bandwidth manager.
> * The helpers encapsulate the sending and received of sideband msgs.
> */
> +struct drm_dp_pending_up_req {
> + struct drm_dp_sideband_msg_hdr hdr;
> + struct drm_dp_sideband_msg_req_body msg;
> + struct list_head next;
> +};
> +
> static bool dump_dp_payload_table(struct drm_dp_mst_topology_mgr *mgr,
> char *buf);
>
> @@ -3109,6 +3115,7 @@ void drm_dp_mst_topology_mgr_suspend(struct
> drm_dp_mst_topology_mgr *mgr)
> drm_dp_dpcd_writeb(mgr->aux, DP_MSTM_CTRL,
> DP_MST_EN | DP_UPSTREAM_IS_SRC);
> mutex_unlock(>lock);
> + flush_work(>up_req_work);
> flush_work(>work);
> flush_work(>delayed_destroy_work);
> }
> @@ -3281,12 +3288,70 @@ static int drm_dp_mst_handle_down_rep(struct
> drm_dp_mst_topology_mgr *mgr)
> return 0;
> }
>
> +static inline void
> +drm_dp_mst_process_up_req(struct drm_dp_mst_topology_mgr *mgr,
> + struct drm_dp_pending_up_req *up_req)
> +{
> + struct drm_dp_mst_branch *mstb = NULL;
> + struct drm_dp_sideband_msg_req_body *msg = _req->msg;
> + struct drm_dp_sideband_msg_hdr *hdr = _req->hdr;
> +
> + if (hdr->broadcast) {
> + const u8 *guid = NULL;
> +
> + if (msg->req_type == DP_CONNECTION_STATUS_NOTIFY)
> + guid = msg->u.conn_stat.guid;
> + else if (msg->req_type == DP_RESOURCE_STATUS_NOTIFY)
> + guid = msg->u.resource_stat.guid;
> +
> + mstb = drm_dp_get_mst_branch_device_by_guid(mgr, guid);
> + } else {
> + mstb = drm_dp_get_mst_branch_device(mgr, hdr->lct, hdr->rad);
> + }
> +
> + if (!mstb) {
> + DRM_DEBUG_KMS("Got MST reply from unknown device %d\n",
> + hdr->lct);
> + return;
> + }
> +
> + /* TODO: Add missing handler for DP_RESOURCE_STATUS_NOTIFY events */
> + if (msg->req_type == DP_CONNECTION_STATUS_NOTIFY) {
> + drm_dp_mst_handle_conn_stat(mstb, >u.conn_stat);
> + drm_kms_helper_hotplug_event(mgr->dev);
> + }
> +
> + drm_dp_mst_topology_put_mstb(mstb);
> +}
> +
> +static void drm_dp_mst_up_req_work(struct work_struct *work)
> +{
> + struct drm_dp_mst_topology_mgr *mgr =
> + container_of(work, struct drm_dp_mst_topology_mgr,
> + up_req_work);
> + struct drm_dp_pending_up_req *up_req;
> +
> + while (true) {
> + mutex_lock(>up_req_lock);
> + up_req =
[Nouveau] [PATCH v2 19/27] drm/dp_mst: Handle UP requests asynchronously
Once upon a time, hotplugging devices on MST branches actually worked in
DRM. Now, it only works in amdgpu (likely because of how it's hotplug
handlers are implemented). On both i915 and nouveau, hotplug
notifications from MST branches are noticed - but trying to respond to
them causes messaging timeouts and causes the whole topology state to go
out of sync with reality, usually resulting in the user needing to
replug the entire topology in hopes that it actually fixes things.
The reason for this is because the way we currently handle UP requests
in MST is completely bogus. drm_dp_mst_handle_up_req() is called from
drm_dp_mst_hpd_irq(), which is usually called from the driver's hotplug
handler. Because we handle sending the hotplug event from this function,
we actually cause the driver's hotplug handler (and in turn, all
sideband transactions) to block on
drm_device->mode_config.connection_mutex. This makes it impossible to
send any sideband messages from the driver's connector probing
functions, resulting in the aforementioned sideband message timeout.
There's even more problems with this beyond breaking hotplugging on MST
branch devices. It also makes it almost impossible to protect
drm_dp_mst_port struct members under a lock because we then have to
worry about dealing with all of the lock dependency issues that ensue.
So, let's finally actually fix this issue by handling the processing of
up requests asyncronously. This way we can send sideband messages from
most contexts without having to deal with getting blocked if we hold
connection_mutex. This also fixes MST branch device hotplugging on i915,
finally!
Cc: Juston Li
Cc: Imre Deak
Cc: Ville Syrjälä
Cc: Harry Wentland
Cc: Daniel Vetter
Signed-off-by: Lyude Paul
---
drivers/gpu/drm/drm_dp_mst_topology.c | 146 +++---
include/drm/drm_dp_mst_helper.h | 16 +++
2 files changed, 122 insertions(+), 40 deletions(-)
diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
b/drivers/gpu/drm/drm_dp_mst_topology.c
index cfaf9eb7ace9..5101eeab4485 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -46,6 +46,12 @@
* protocol. The helpers contain a topology manager and bandwidth manager.
* The helpers encapsulate the sending and received of sideband msgs.
*/
+struct drm_dp_pending_up_req {
+ struct drm_dp_sideband_msg_hdr hdr;
+ struct drm_dp_sideband_msg_req_body msg;
+ struct list_head next;
+};
+
static bool dump_dp_payload_table(struct drm_dp_mst_topology_mgr *mgr,
char *buf);
@@ -3109,6 +3115,7 @@ void drm_dp_mst_topology_mgr_suspend(struct
drm_dp_mst_topology_mgr *mgr)
drm_dp_dpcd_writeb(mgr->aux, DP_MSTM_CTRL,
DP_MST_EN | DP_UPSTREAM_IS_SRC);
mutex_unlock(>lock);
+ flush_work(>up_req_work);
flush_work(>work);
flush_work(>delayed_destroy_work);
}
@@ -3281,12 +3288,70 @@ static int drm_dp_mst_handle_down_rep(struct
drm_dp_mst_topology_mgr *mgr)
return 0;
}
+static inline void
+drm_dp_mst_process_up_req(struct drm_dp_mst_topology_mgr *mgr,
+ struct drm_dp_pending_up_req *up_req)
+{
+ struct drm_dp_mst_branch *mstb = NULL;
+ struct drm_dp_sideband_msg_req_body *msg = _req->msg;
+ struct drm_dp_sideband_msg_hdr *hdr = _req->hdr;
+
+ if (hdr->broadcast) {
+ const u8 *guid = NULL;
+
+ if (msg->req_type == DP_CONNECTION_STATUS_NOTIFY)
+ guid = msg->u.conn_stat.guid;
+ else if (msg->req_type == DP_RESOURCE_STATUS_NOTIFY)
+ guid = msg->u.resource_stat.guid;
+
+ mstb = drm_dp_get_mst_branch_device_by_guid(mgr, guid);
+ } else {
+ mstb = drm_dp_get_mst_branch_device(mgr, hdr->lct, hdr->rad);
+ }
+
+ if (!mstb) {
+ DRM_DEBUG_KMS("Got MST reply from unknown device %d\n",
+ hdr->lct);
+ return;
+ }
+
+ /* TODO: Add missing handler for DP_RESOURCE_STATUS_NOTIFY events */
+ if (msg->req_type == DP_CONNECTION_STATUS_NOTIFY) {
+ drm_dp_mst_handle_conn_stat(mstb, >u.conn_stat);
+ drm_kms_helper_hotplug_event(mgr->dev);
+ }
+
+ drm_dp_mst_topology_put_mstb(mstb);
+}
+
+static void drm_dp_mst_up_req_work(struct work_struct *work)
+{
+ struct drm_dp_mst_topology_mgr *mgr =
+ container_of(work, struct drm_dp_mst_topology_mgr,
+up_req_work);
+ struct drm_dp_pending_up_req *up_req;
+
+ while (true) {
+ mutex_lock(>up_req_lock);
+ up_req = list_first_entry_or_null(>up_req_list,
+ struct drm_dp_pending_up_req,
+ next);
+ if (up_req)
+ list_del(_req->next);
+
