RE: [PATCH] drm/dp_mst: Clear MSG_RDY flag before sending new message

[AMD Official Use Only - General]

Hi Lyude,

Much appreciated! Will update and send out another version.

Thanks, Wayne Lin

-----Original Message----- From: Lyude Paul lyude@redhat.com Sent: Wednesday, June 7, 2023 6:03 AM To: Lin, Wayne Wayne.Lin@amd.com; amd-gfx@lists.freedesktop.org Cc: ville.syrjala@linux.intel.com; jani.nikula@intel.com; imre.deak@intel.com; Wentland, Harry Harry.Wentland@amd.com; Zuo, Jerry Jerry.Zuo@amd.com; stable@vger.kernel.org Subject: Re: [PATCH] drm/dp_mst: Clear MSG_RDY flag before sending new message

My apologies for taking so long to reply to this. I'll be honest - the last MST fiasco seriously burned me out big time, and I had to take a big step back from working on MST for a while. Comments below

On Wed, 2023-05-31 at 12:00 +0800, Wayne Lin wrote:

...

[Why] The sequence for collecting down_reply from source perspective should be:

Request_n->repeat (get partial reply of Request_n->clear message ready flag to ack DPRX that the message is received) till all partial replies for Request_n are received->new Request_n+1.

Now there is chance that drm_dp_mst_hpd_irq() will fire new down request in the tx queue when the down reply is incomplete. Source is restricted to generate interveleaved message transactions so we should avoid it.

Also, while assembling partial reply packets, reading out DPCD DOWN_REP Sideband MSG buffer + clearing DOWN_REP_MSG_RDY flag

should

...

be wrapped up as a complete operation for reading out a reply packet. Kicking off a new request before clearing DOWN_REP_MSG_RDY flag might be risky. e.g. If the reply of the new request has overwritten the DPRX DOWN_REP Sideband MSG buffer before source writing one to clear DOWN_REP_MSG_RDY flag, source then unintentionally flushes the reply for the new request. Should handle the up request in the same way.

[How] Separete drm_dp_mst_hpd_irq() into 2 steps. After acking the MST IRQ event, driver calls drm_dp_mst_hpd_irq_send_new_request() and might trigger drm_dp_mst_kick_tx() only when there is no on going message transaction.

Changes since v1:

• Reworked on review comments received

-> Adjust the fix to let driver explicitly kick off new down request when mst irq event is handled and acked -> Adjust the commit message

Changes since v2:

• Adjust the commit message
• Adjust the naming of the divided 2 functions and add a new input parameter "ack".
• Adjust code flow as per review comments.

Signed-off-by: Wayne Lin Wayne.Lin@amd.com Cc: stable@vger.kernel.org

---

.../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 33 +++++++++-----

--

...

drivers/gpu/drm/display/drm_dp_mst_topology.c | 39

+++++++++++++++++--

...

drivers/gpu/drm/i915/display/intel_dp.c | 7 ++-- drivers/gpu/drm/nouveau/dispnv50/disp.c | 12 ++++-- include/drm/display/drm_dp_mst_helper.h | 7 +++- 5 files changed, 70 insertions(+), 28 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c index d5cec03eaa8d..597c3368bcfb 100644 --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c @@ -3236,6 +3236,7 @@ static void dm_handle_mst_sideband_msg(struct amdgpu_dm_connector *aconnector) { u8 esi[DP_PSR_ERROR_STATUS - DP_SINK_COUNT_ESI] = { 0 }; u8 dret;

• u8 ack; bool new_irq_handled = false; int dpcd_addr; int dpcd_bytes_to_read;

@@ -3265,34 +3266,36 @@ static void

dm_handle_mst_sideband_msg(struct amdgpu_dm_connector *aconnector)

...

        process_count < max_process_count) {
        u8 retry;
        dret = 0;

•       ack = 0;
  
        process_count++;
  
        DRM_DEBUG_DRIVER("ESI %02x %02x %02x\n", esi[0],
  

esi[1], esi[2]);

...

        /* handle HPD short pulse irq */
        if (aconnector->mst_mgr.mst_state)

•               drm_dp_mst_hpd_irq(
  

•                       &aconnector->mst_mgr,
  

•                       esi,
  

•                       &new_irq_handled);
  

•               drm_dp_mst_hpd_irq_handle_event(&aconnector-
  

mst_mgr,

•                                               esi,
  

•                                               &ack,
  

•                                               &new_irq_handled);
  
        if (new_irq_handled) {
                /* ACK at DPCD to notify down stream */
  

•               const int ack_dpcd_bytes_to_write =
  

•                       dpcd_bytes_to_read - 1;
  

•               for (retry = 0; retry < 3; retry++) {
  

•                       u8 wret;
  

•                       wret = drm_dp_dpcd_write(
  

•                               &aconnector->dm_dp_aux.aux,
  

•                               dpcd_addr + 1,
  

•                               &esi[1],
  

•                               ack_dpcd_bytes_to_write);
  

•                       if (wret == ack_dpcd_bytes_to_write)
  

•                       ssize_t wret;
  

•                       wret = drm_dp_dpcd_writeb(&aconnector-
  

dm_dp_aux.aux,

•                                                 dpcd_addr + 1,
  

•                                                 ack);
  

•                       if (wret == 1)
                                break;
                }
  
  

•               if (retry == 3) {
  

•                       DRM_ERROR("Failed to ack MST event.\n");
  

•                       return;
  

•               }
  

  drm_dp_mst_hpd_irq_send_new_request(&aconnector->mst_mgr);

...

                /* check if there is new irq to be handled */
                dret = drm_dp_dpcd_read(
                        &aconnector->dm_dp_aux.aux,

diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c b/drivers/gpu/drm/display/drm_dp_mst_topology.c index 38dab76ae69e..13165e764709 100644 --- a/drivers/gpu/drm/display/drm_dp_mst_topology.c +++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c @@ -4053,9 +4053,10 @@ static int drm_dp_mst_handle_up_req(struct drm_dp_mst_topology_mgr *mgr) }

/**

• • drm_dp_mst_hpd_irq() - MST hotplug IRQ notify

• • drm_dp_mst_hpd_irq_handle_event() - MST hotplug IRQ handle MST
• event
  • @mgr: manager to notify irq for.
  • @esi: 4 bytes from SINK_COUNT_ESI
• • @ack: flags of events to ack
  • @handled: whether the hpd interrupt was consumed or not
  • This should be called from the driver when it detects a short IRQ,

@@ -4063,7 +4064,8 @@ static int drm_dp_mst_handle_up_req(struct

drm_dp_mst_topology_mgr *mgr)

...

• topology manager will process the sideband messages received as a result
• of this.

We've gotta update the documentation here to reflect the changes being made. Otherwise I think this looks good. Mind sending out a new version and I will confirm this works on nouveau's side before giving an RB

(That might take a day or two, I accidentally discovered nouveau's MST support regressed a bit while I was away :( )

...

*/ -int drm_dp_mst_hpd_irq(struct drm_dp_mst_topology_mgr *mgr, u8 *esi, bool *handled) +int drm_dp_mst_hpd_irq_handle_event(struct drm_dp_mst_topology_mgr

*mgr, const u8 *esi,

...

•                           u8 *ack, bool *handled)
  

{ int ret = 0; int sc; @@ -4078,18 +4080,47 @@ int drm_dp_mst_hpd_irq(struct

drm_dp_mst_topology_mgr *mgr, u8 *esi, bool *handl

...

if (esi[1] & DP_DOWN_REP_MSG_RDY) {
        ret = drm_dp_mst_handle_down_rep(mgr);
        *handled = true;

•       *ack |= DP_DOWN_REP_MSG_RDY;
  

  }

  if (esi[1] & DP_UP_REQ_MSG_RDY) { ret |= drm_dp_mst_handle_up_req(mgr); *handled = true;

•       *ack |= DP_UP_REQ_MSG_RDY;
  

  }

• drm_dp_mst_kick_tx(mgr); return ret;

} -EXPORT_SYMBOL(drm_dp_mst_hpd_irq); +EXPORT_SYMBOL(drm_dp_mst_hpd_irq_handle_event);

+/**

• • drm_dp_mst_hpd_irq_send_new_request() - MST hotplug IRQ kick off

+new request

• • @mgr: manager to notify irq for.
• • This should be called from the driver when mst irq event is

+handled

• • and acked. Note that new down request should only be sent when
• • previous message transaction is completed. Source is not supposed

+to generate

• • interleaved message transactions.
• */

+void drm_dp_mst_hpd_irq_send_new_request(struct +drm_dp_mst_topology_mgr *mgr) {

• struct drm_dp_sideband_msg_tx *txmsg;

• bool kick = true;

• mutex_lock(&mgr->qlock);

• txmsg = list_first_entry_or_null(&mgr->tx_msg_downq,

•                                struct drm_dp_sideband_msg_tx,
  

next);

...

• /* If last transaction is not completed yet*/
• if (!txmsg ||

•   txmsg->state == DRM_DP_SIDEBAND_TX_START_SEND ||
  

•   txmsg->state == DRM_DP_SIDEBAND_TX_SENT)
  

•       kick = false;
  

• mutex_unlock(&mgr->qlock);
• if (kick)

•       drm_dp_mst_kick_tx(mgr);
  

+} +EXPORT_SYMBOL(drm_dp_mst_hpd_irq_send_new_request); /**

• drm_dp_mst_detect_port() - get connection status for an MST port
• @connector: DRM connector for this port diff --git

a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c index 4bec8cd7979f..f24602887015 100644 --- a/drivers/gpu/drm/i915/display/intel_dp.c +++ b/drivers/gpu/drm/i915/display/intel_dp.c @@ -4062,9 +4062,7 @@ intel_dp_mst_hpd_irq(struct intel_dp *intel_dp, u8 *esi, u8 *ack) { bool handled = false;

• drm_dp_mst_hpd_irq(&intel_dp->mst_mgr, esi, &handled);
• if (handled)

•       ack[1] |= esi[1] & (DP_DOWN_REP_MSG_RDY |
  

DP_UP_REQ_MSG_RDY);

...

• drm_dp_mst_hpd_irq_handle_event(&intel_dp->mst_mgr, esi,

&ack[1],

...

+&handled);

if (esi[1] & DP_CP_IRQ) {
        intel_hdcp_handle_cp_irq(intel_dp->attached_connector);

@@ -4139,6 +4137,9 @@ intel_dp_check_mst_status(struct intel_dp *intel_dp)

        if (!intel_dp_ack_sink_irq_esi(intel_dp, ack))
                drm_dbg_kms(&i915->drm, "Failed to ack ESI\n");

•       if (ack[1] & (DP_DOWN_REP_MSG_RDY |
  

DP_UP_REQ_MSG_RDY))

...

•               drm_dp_mst_hpd_irq_send_new_request(&intel_dp-
  

mst_mgr); }

return link_ok;

diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c b/drivers/gpu/drm/nouveau/dispnv50/disp.c index 9b6824f6b9e4..b2d9978e88a8 100644 --- a/drivers/gpu/drm/nouveau/dispnv50/disp.c +++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c @@ -1357,6 +1357,7 @@ nv50_mstm_service(struct nouveau_drm *drm, bool handled = true, ret = true; int rc; u8 esi[8] = {};

• u8 ack;

  while (handled) { rc = drm_dp_dpcd_read(aux, DP_SINK_COUNT_ESI, esi, 8);

@@ -1365,16

...

+1366,19 @@ nv50_mstm_service(struct nouveau_drm *drm, break; }

•       drm_dp_mst_hpd_irq(&mstm->mgr, esi, &handled);
  

•       ack = 0;
  

•       drm_dp_mst_hpd_irq_handle_event(&mstm->mgr, esi, &ack,
  

&handled);

...

        if (!handled)
                break;

•       rc = drm_dp_dpcd_write(aux, DP_SINK_COUNT_ESI + 1,
  

&esi[1],

...

•                              3);
  

•       if (rc != 3) {
  

•       rc = drm_dp_dpcd_writeb(aux, DP_SINK_COUNT_ESI + 1,
  

ack);

...

•       if (rc != 1) {
                ret = false;
                break;
        }
  

•       drm_dp_mst_hpd_irq_send_new_request(&mstm->mgr);
  

  }

  if (!ret)

diff --git a/include/drm/display/drm_dp_mst_helper.h b/include/drm/display/drm_dp_mst_helper.h index 32c764fb9cb5..40e855c8407c 100644 --- a/include/drm/display/drm_dp_mst_helper.h +++ b/include/drm/display/drm_dp_mst_helper.h @@ -815,8 +815,11 @@ void drm_dp_mst_topology_mgr_destroy(struct drm_dp_mst_topology_mgr *mgr); bool drm_dp_read_mst_cap(struct drm_dp_aux *aux, const u8 dpcd[DP_RECEIVER_CAP_SIZE]); int drm_dp_mst_topology_mgr_set_mst(struct drm_dp_mst_topology_mgr

*mgr,

...

bool mst_state);

-int drm_dp_mst_hpd_irq(struct drm_dp_mst_topology_mgr *mgr, u8 *esi, bool *handled);

+int drm_dp_mst_hpd_irq_handle_event(struct drm_dp_mst_topology_mgr

*mgr,

...

•                           const u8 *esi,
  

•                           u8 *ack,
  

•                           bool *handled);
  

+void drm_dp_mst_hpd_irq_send_new_request(struct +drm_dp_mst_topology_mgr *mgr);

int drm_dp_mst_detect_port(struct drm_connector *connector,

-- Cheers, Lyude Paul (she/her) Software Engineer at Red Hat