[PATCH] drm/dp_mst: Clear MSG_RDY flag before sending new message
Jani Nikula
jani.nikula at intel.com
Tue Apr 18 11:58:42 UTC 2023
On Tue, 18 Apr 2023, "Lin, Wayne" <Wayne.Lin at amd.com> wrote:
> [Public]
>
> Hi Jani Nikula,
>
> Appreciate your time and feedback! Will adjust the patch.
> Some comments inline.
>
>> -----Original Message-----
>> From: Jani Nikula <jani.nikula at intel.com>
>> Sent: Tuesday, April 18, 2023 4:53 PM
>> To: Lin, Wayne <Wayne.Lin at amd.com>; dri-devel at lists.freedesktop.org;
>> amd-gfx at lists.freedesktop.org
>> Cc: lyude at redhat.com; imre.deak at intel.com; ville.syrjala at linux.intel.com;
>> Wentland, Harry <Harry.Wentland at amd.com>; Zuo, Jerry
>> <Jerry.Zuo at amd.com>; Lin, Wayne <Wayne.Lin at amd.com>;
>> stable at vger.kernel.org
>> Subject: Re: [PATCH] drm/dp_mst: Clear MSG_RDY flag before sending new
>> message
>>
>> On Tue, 18 Apr 2023, Wayne Lin <Wayne.Lin at amd.com> wrote:
>> > [Why & How]
>> > The sequence for collecting down_reply/up_request 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.
>> >
>> > 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 ack 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.
>> >
>> > In drm_dp_mst_hpd_irq(), we don't clear MSG_RDY flag before caliing
>> > drm_dp_mst_kick_tx(). Fix that.
>> >
>> > Signed-off-by: Wayne Lin <Wayne.Lin at amd.com>
>> > Cc: stable at vger.kernel.org
>> > ---
>> > .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 2 ++
>> > drivers/gpu/drm/display/drm_dp_mst_topology.c | 22
>> +++++++++++++++++++
>> > drivers/gpu/drm/i915/display/intel_dp.c | 3 +++
>> > drivers/gpu/drm/nouveau/dispnv50/disp.c | 2 ++
>> > 4 files changed, 29 insertions(+)
>> >
>> > 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 77277d90b6e2..5313a5656598 100644
>> > --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>> > +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>> > @@ -3166,6 +3166,8 @@ static void dm_handle_mst_sideband_msg(struct
>> amdgpu_dm_connector *aconnector)
>> > for (retry = 0; retry < 3; retry++) {
>> > uint8_t wret;
>> >
>> > + /* MSG_RDY ack is done in drm*/
>> > + esi[1] &= ~(DP_DOWN_REP_MSG_RDY |
>> DP_UP_REQ_MSG_RDY);
>>
>> Why do the masking within the retry loop?
>>
>> > wret = drm_dp_dpcd_write(
>> > &aconnector->dm_dp_aux.aux,
>> > dpcd_addr + 1,
>> > diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c
>> > b/drivers/gpu/drm/display/drm_dp_mst_topology.c
>> > index 51a46689cda7..02aad713c67c 100644
>> > --- a/drivers/gpu/drm/display/drm_dp_mst_topology.c
>> > +++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c
>> > @@ -4054,6 +4054,9 @@ int drm_dp_mst_hpd_irq(struct
>> > drm_dp_mst_topology_mgr *mgr, u8 *esi, bool *handl {
>> > int ret = 0;
>> > int sc;
>> > + const int tosend = 1;
>> > + int retries = 0;
>> > + u8 buf = 0;
>>
>> All of these should be in tighter scope.
>>
>> > *handled = false;
>> > sc = DP_GET_SINK_COUNT(esi[0]);
>> >
>> > @@ -4072,6 +4075,25 @@ int drm_dp_mst_hpd_irq(struct
>> drm_dp_mst_topology_mgr *mgr, u8 *esi, bool *handl
>> > *handled = true;
>> > }
>> >
>> > + if (*handled) {
>>
>> That should check for DP_DOWN_REP_MSG_RDY and
>> DP_UP_REQ_MSG_RDY only, right? If those are not set, we didn't do
>> anything with them, and should not ack.
>
> Right. I was thinking the sink count change will accompany the CSN
> up request message. I'll change it to be more clear. Thanks.
>>
>> > + buf = esi[1] & (DP_DOWN_REP_MSG_RDY |
>> DP_UP_REQ_MSG_RDY);
>> > + do {
>> > + ret = drm_dp_dpcd_write(mgr->aux,
>> > +
>> DP_DEVICE_SERVICE_IRQ_VECTOR_ESI0,
>> > + &buf,
>> > + tosend);
>>
>> We should probably have a helper function to do the acking, similar to
>> intel_dp_ack_sink_irq_esi(), which could be used both by this function and
>> the drivers.
>>
>> > +
>> > + if (ret == tosend)
>> > + break;
>> > +
>> > + retries++;
>> > + } while (retries < 5);
>>
>> Please don't use a do-while when a for loop is sufficient.
>>
>> for (tries = 0; tries < 5; tries++)
>>
>> and it's obvious at a glance how many times at most this runs. Not so with a
>> do-while where you count *re-tries*. Again, would be nice to abstract this
>> away in a helper function.
>>
>> > +
>> > + if (ret != tosend)
>> > + drm_dbg_kms(mgr->dev, "failed to write dpcd
>> 0x%x\n",
>> > + DP_DEVICE_SERVICE_IRQ_VECTOR_ESI0);
>> > + }
>> > +
>> > drm_dp_mst_kick_tx(mgr);
>> > return ret;
>> > }
>> > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c
>> > b/drivers/gpu/drm/i915/display/intel_dp.c
>> > index bf80f296a8fd..abec3de38b66 100644
>> > --- a/drivers/gpu/drm/i915/display/intel_dp.c
>> > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
>> > @@ -3939,6 +3939,9 @@ intel_dp_check_mst_status(struct intel_dp
>> *intel_dp)
>> > if (!memchr_inv(ack, 0, sizeof(ack)))
>> > break;
>> >
>> > + /* MSG_RDY ack is done in drm*/
>> > + ack[1] &= ~(DP_DOWN_REP_MSG_RDY |
>> DP_UP_REQ_MSG_RDY);
>>
>> Above we check if there's anything to ack and bail out, and now this clears
>> the bits but writes them anyway.
>>
>> I think the handled parameter was problematic before, but now it's even
>> more convoluted. What does it indicate? It used to mean you need to ack if
>> it's set, but now it's something different. This function is getting very difficult
>> to use correctly.
>
> My plan was to ack message events within drm_dp_mst_hpd_irq() since the
> events are handled there. There are still CP_IRQ and LINK_STATUS_CHANGED
> events above get handled in intel_dp_check_mst_status(), so I intended to
> mask DP_DOWN_REP_MSG_RDY/DP_UP_REQ_MSG_RDY, and ack
> CP_IRQ/LINK_STATUS_CHANGED here.
I get it, but if DP_DOWN_REP_MSG_RDY or DP_UP_REQ_MSG_RDY were the only
events to ack, and they were already acked in drm_dp_mst_hpd_irq(), we
should not do an extra "nop" ack.
The caller of drm_dp_mst_hpd_irq() needs to be able to conveniently
figure out what to ack, and what to not ack. And without duplicating the
logic within drm_dp_mst_hpd_irq().
BR,
Jani.
>>
>> BR,
>> Jani.
>>
>>
>>
>> > +
>> > if (!intel_dp_ack_sink_irq_esi(intel_dp, ack))
>> > drm_dbg_kms(&i915->drm, "Failed to ack ESI\n");
>> > }
>> > diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c
>> > b/drivers/gpu/drm/nouveau/dispnv50/disp.c
>> > index edcb2529b402..e905987104ed 100644
>> > --- a/drivers/gpu/drm/nouveau/dispnv50/disp.c
>> > +++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c
>> > @@ -1336,6 +1336,8 @@ nv50_mstm_service(struct nouveau_drm *drm,
>> > if (!handled)
>> > break;
>> >
>> > + /* MSG_RDY ack is done in drm*/
>> > + esi[1] &= ~(DP_DOWN_REP_MSG_RDY |
>> DP_UP_REQ_MSG_RDY);
>> > rc = drm_dp_dpcd_write(aux, DP_SINK_COUNT_ESI + 1,
>> &esi[1],
>> > 3);
>>
>> Same here, this acks even if it's already been acked.
>>
>> > if (rc != 3) {
>>
>> --
>> Jani Nikula, Intel Open Source Graphics Center
>
> --
> Regards,
> Wayne Lin
--
Jani Nikula, Intel Open Source Graphics Center
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