[Public]
Hi Jani,
Thanks for your time!
Comments inline.
> -----Original Message-----
> From: Jani Nikula <jani.nikula@xxxxxxxxx>
> Sent: Tuesday, May 16, 2023 6:34 PM
> To: Lin, Wayne <Wayne.Lin@xxxxxxx>; dri-devel@xxxxxxxxxxxxxxxxxxxxx;
> amd-gfx@xxxxxxxxxxxxxxxxxxxxx
> Cc: lyude@xxxxxxxxxx; ville.syrjala@xxxxxxxxxxxxxxx; imre.deak@xxxxxxxxx;
> Wentland, Harry <Harry.Wentland@xxxxxxx>; Zuo, Jerry
> <Jerry.Zuo@xxxxxxx>; Lin, Wayne <Wayne.Lin@xxxxxxx>;
> stable@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH v2] drm/dp_mst: Clear MSG_RDY flag before sending new
> message
>
> On Thu, 27 Apr 2023, Wayne Lin <Wayne.Lin@xxxxxxx> 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_step2() 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
> >
> > Signed-off-by: Wayne Lin <Wayne.Lin@xxxxxxx>
> > Cc: stable@xxxxxxxxxxxxxxx
> > ---
> > .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 8 ++---
> > drivers/gpu/drm/display/drm_dp_mst_topology.c | 35
> ++++++++++++++++---
> > drivers/gpu/drm/i915/display/intel_dp.c | 5 ++-
> > drivers/gpu/drm/nouveau/dispnv50/disp.c | 5 ++-
> > include/drm/display/drm_dp_mst_helper.h | 4 +--
> > 5 files changed, 45 insertions(+), 12 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 1ad67c2a697e..48bdcb2ee9b1 100644
> > --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> > +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> > @@ -3259,10 +3259,9 @@ static void
> dm_handle_mst_sideband_msg(struct amdgpu_dm_connector *aconnector)
> > 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_step1(&aconnector->mst_mgr,
> > + esi,
> > + &new_irq_handled);
> >
> > if (new_irq_handled) {
> > /* ACK at DPCD to notify down stream */ @@ -
> 3281,6 +3280,7 @@
> > static void dm_handle_mst_sideband_msg(struct amdgpu_dm_connector
> *aconnector)
> > break;
> > }
> >
> > + drm_dp_mst_hpd_irq_step2(&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 70df29fe92db..2e0a38a6509c 100644
> > --- a/drivers/gpu/drm/display/drm_dp_mst_topology.c
> > +++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c
> > @@ -4045,7 +4045,7 @@ 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_step1() - MST hotplug IRQ notify
> > * @mgr: manager to notify irq for.
> > * @esi: 4 bytes from SINK_COUNT_ESI
> > * @handled: whether the hpd interrupt was consumed or not @@ -4055,7
> > +4055,7 @@ 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.
> > */
> > -int drm_dp_mst_hpd_irq(struct drm_dp_mst_topology_mgr *mgr, u8 *esi,
> > bool *handled)
> > +int drm_dp_mst_hpd_irq_step1(struct drm_dp_mst_topology_mgr *mgr,
> u8
> > +*esi, bool *handled)
>
> If you're changing the signature of the function, I'd make esi "const u8 *esi",
> and add a separate "u8 *ack" that you have to provide, where this function
> would |= the flags to ack. It would be useful at least in i915.
Will adjust. Thanks.
>
> As to naming, _step1 and _step2 are pretty vague.
Was trying to align the naming method we used for payload allocation/de-allocation.
Anyway, I'll adjust the naming here.
>
> > {
> > int ret = 0;
> > int sc;
> > @@ -4077,11 +4077,38 @@ int drm_dp_mst_hpd_irq(struct
> drm_dp_mst_topology_mgr *mgr, u8 *esi, bool *handl
> > *handled = true;
> > }
> >
> > - drm_dp_mst_kick_tx(mgr);
> > return ret;
> > }
> > -EXPORT_SYMBOL(drm_dp_mst_hpd_irq);
> > +EXPORT_SYMBOL(drm_dp_mst_hpd_irq_step1);
> > +
> > +/**
> > + * drm_dp_mst_hpd_irq_step2() - MST hotplug IRQ 2nd part handling
> > + * @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 done. Source is not supposed to
> > +generate
> > + * interleaved message transactions.
> > + */
> > +void drm_dp_mst_hpd_irq_step2(struct drm_dp_mst_topology_mgr
> *mgr)
>
> _done, _finish, _complete?
Will use "complete". Thanks.
>
> > +{
> > + struct drm_dp_sideband_msg_tx *txmsg;
> > + bool skip = false;
> >
> > + 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)
> > + skip = true;
> > + mutex_unlock(&mgr->qlock);
> > +
> > + if (!skip)
>
> Please avoid negatives like this. You could have bool kick = true instead.
Thanks. Will modify it.
>
> > + drm_dp_mst_kick_tx(mgr);
> > +}
> > +EXPORT_SYMBOL(drm_dp_mst_hpd_irq_step2);
> > /**
> > * 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 75070eb07d4b..9a9a5aec9534 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> > @@ -3803,7 +3803,7 @@ 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);
> > + drm_dp_mst_hpd_irq_step1(&intel_dp->mst_mgr, esi, &handled);
> > if (handled)
> > ack[1] |= esi[1] & (DP_DOWN_REP_MSG_RDY |
> DP_UP_REQ_MSG_RDY);
> >
> > @@ -3880,6 +3880,9 @@ 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_step2(&intel_dp->mst_mgr);
>
> I'm getting confused about the division of responsibilities between the two
> functions to be called, and the caller. Why does i915 do things differently from
> nouveau and amd wrt this?
The main idea is trying to ack the irq before sending a new request. We used to
send a new request before acking the irq event which will cause message interleaving
and that's not recommended by DP spec.
amd and nouveau only handle mst up/down message irq events while calling
drm_dp_mst_hpd_irq() but i915 also tries to handle content protection irq while
handling mst events. That's why it's a bit different between amd/nouveau and i915.
>
> > }
> >
> > return link_ok;
> > diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c
> > b/drivers/gpu/drm/nouveau/dispnv50/disp.c
> > index ed9d374147b8..00c36fcc8afd 100644
> > --- a/drivers/gpu/drm/nouveau/dispnv50/disp.c
> > +++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c
> > @@ -1332,12 +1332,15 @@ nv50_mstm_service(struct nouveau_drm
> *drm,
> > break;
> > }
> >
> > - drm_dp_mst_hpd_irq(&mstm->mgr, esi, &handled);
> > + drm_dp_mst_hpd_irq_step1(&mstm->mgr, esi, &handled);
> > if (!handled)
> > break;
> >
> > rc = drm_dp_dpcd_write(aux, DP_SINK_COUNT_ESI + 1,
> &esi[1],
> > 3);
> > +
> > + drm_dp_mst_hpd_irq_step2(&mstm->mgr);
> > +
>
> Don't you think the return value should be checked first?
Sorry I missed it. Will adjust. Thanks!
>
> > if (rc != 3) {
> > ret = false;
> > break;
> > diff --git a/include/drm/display/drm_dp_mst_helper.h
> > b/include/drm/display/drm_dp_mst_helper.h
> > index 32c764fb9cb5..6c08ba765d5a 100644
> > --- a/include/drm/display/drm_dp_mst_helper.h
> > +++ b/include/drm/display/drm_dp_mst_helper.h
> > @@ -815,8 +815,8 @@ 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_step1(struct drm_dp_mst_topology_mgr *mgr,
> u8
> > +*esi, bool *handled); void drm_dp_mst_hpd_irq_step2(struct
> > +drm_dp_mst_topology_mgr *mgr);
> >
> > int
> > drm_dp_mst_detect_port(struct drm_connector *connector,
>
> --
> Jani Nikula, Intel Open Source Graphics Center
--
Regards,
Wayne Lin
