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....@amd.com>
> Cc: sta...@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
