[PATCH 3/3] drm/dp_mst: Remove single tx msg restriction.
Sean Paul
sean at poorly.run
Tue Feb 18 17:15:22 UTC 2020
On Tue, Feb 18, 2020 at 10:52:06AM -0500, Sean Paul wrote:
> On Mon, Feb 17, 2020 at 07:08:37AM +0000, Lin, Wayne wrote:
> > [AMD Public Use]
> >
> >
> >
> > > -----Original Message-----
> > > From: Sean Paul <sean at poorly.run>
> > > Sent: Saturday, February 15, 2020 12:09 AM
> > > To: Lin, Wayne <Wayne.Lin at amd.com>
> > > Cc: dri-devel at lists.freedesktop.org; lyude at redhat.com; Sean Paul
> > > <seanpaul at chromium.org>; Maarten Lankhorst
> > > <maarten.lankhorst at linux.intel.com>; Maxime Ripard <mripard at kernel.org>;
> > > David Airlie <airlied at linux.ie>
> > > Subject: Re: [PATCH 3/3] drm/dp_mst: Remove single tx msg restriction.
> > >
> > > On Fri, Feb 14, 2020 at 12:58 AM Lin, Wayne <Wayne.Lin at amd.com> wrote:
> > > >
> > > > [AMD Public Use]
> > > >
> > > > Hi Paul,
> > > >
> > > > Thanks for the mail!
> > > >
> > > > I tried to solve this problem by having restriction on sending one msg at a
> > > time due to hub/dock compatibility problems.
> > > > From my experience, some branch devices don't handle well on
> > > > interleaved replies (Dock from HP I think)
> > >
> > > Hi Wayne,
> > > Hmm, that's interesting, do you have a part number of the failing dock so I can
> > > test it?
> > >
> > Hi Paul,
> >
> > Sorry but it's been quite a while. I can't exactly tell the part number.
> > If I remember correctly, when the specific branch device receives interleaved replies,
> > it just doesn't reply to any requests.
> >
> > > > As the result of that, correct me if I'm wrong, I remember most gpu vendors
> > > just send one down request at a time now in windows environment.
> > > > I would suggest the original solution :)
> > >
> > > I can't really say what happens on the Windows side of the world, but I suppose
> > > that makes sense if this is a widespread issue with docks. I do worry about the
> > > performance hit.
> > >
> > > If indeed this is a problem, could we ratelimit per branch device instead of
> > > globally? Even that would be better than serializing everything.
> > >
> > Since the problem was because some branch devices can't simultaneously handle
> > two replies, I'm afraid that we might still encounter the same problem?
> >
>
> Hi Wayne,
> Thanks for clarifying. I'm a bit hesitant to scrap this idea without solid
> evidence that this is a common problem. Do you have any hubs around AMD that
> you could try my patchset with?
Oh, if you can test the set, you'll also need this patch as well :-)
diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -3814,7 +3814,9 @@ static bool drm_dp_get_one_sb_msg(struct drm_dp_mst_topology_mgr *mgr, bool up,
int basereg = up ? DP_SIDEBAND_MSG_UP_REQ_BASE :
DP_SIDEBAND_MSG_DOWN_REP_BASE;
- *mstb = NULL;
+ if (mstb)
+ *mstb = NULL;
+
*seqno = -1;
len = min(mgr->max_dpcd_transaction_bytes, 16);
> Perhaps we could get some hard data? I'm happy
> to test things on my end, but I probably shouldn't just start buying a bunch of
> random HP docks in hopes one of them exhibits the issue :)
>
> To add anecdote to anecdote, everything on my desk seems to work with
> interleaved replies.
>
> Since HDCP spec requires the host to verify each channel's encryption every <2s,
> we're going to be increasing the amount of sideband traffic a fair amount, so I
> would like to ensure we're doing everything possible to maximize our sideband
> bandwidth.
>
> Sean
>
> > Thanks!
> > > Sean
> > >
> > > >
> > > > Thanks!
> > > > > -----Original Message-----
> > > > > From: Sean Paul <sean at poorly.run>
> > > > > Sent: Friday, February 14, 2020 5:15 AM
> > > > > To: dri-devel at lists.freedesktop.org
> > > > > Cc: lyude at redhat.com; Lin, Wayne <Wayne.Lin at amd.com>; Sean Paul
> > > > > <seanpaul at chromium.org>; Maarten Lankhorst
> > > > > <maarten.lankhorst at linux.intel.com>; Maxime Ripard
> > > > > <mripard at kernel.org>; David Airlie <airlied at linux.ie>
> > > > > Subject: [PATCH 3/3] drm/dp_mst: Remove single tx msg restriction.
> > > > >
> > > > > From: Sean Paul <seanpaul at chromium.org>
> > > > >
> > > > > Now that we can support multiple simultaneous replies, remove the
> > > > > restrictions placed on sending new tx msgs.
> > > > >
> > > > > This patch essentially just reverts commit
> > > > > 5a64967a2f3b ("drm/dp_mst: Have DP_Tx send one msg at a time")
> > > now
> > > > > that the problem is solved in a different way.
> > > > >
> > > > > Cc: Wayne Lin <Wayne.Lin at amd.com>
> > > > > Signed-off-by: Sean Paul <seanpaul at chromium.org>
> > > > > ---
> > > > > drivers/gpu/drm/drm_dp_mst_topology.c | 14 ++------------
> > > > > include/drm/drm_dp_mst_helper.h | 6 ------
> > > > > 2 files changed, 2 insertions(+), 18 deletions(-)
> > > > >
> > > > > diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> > > > > b/drivers/gpu/drm/drm_dp_mst_topology.c
> > > > > index 7e6a82efdfc02..cbf0bb0ddeb84 100644
> > > > > --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> > > > > +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> > > > > @@ -1203,8 +1203,6 @@ static int drm_dp_mst_wait_tx_reply(struct
> > > > > drm_dp_mst_branch *mstb,
> > > > > txmsg->state == DRM_DP_SIDEBAND_TX_SENT) {
> > > > > mstb->tx_slots[txmsg->seqno] = NULL;
> > > > > }
> > > > > - mgr->is_waiting_for_dwn_reply = false;
> > > > > -
> > > > > }
> > > > > out:
> > > > > if (unlikely(ret == -EIO) && drm_debug_enabled(DRM_UT_DP)) {
> > > > > @@
> > > > > -1214,7 +1212,6 @@ static int drm_dp_mst_wait_tx_reply(struct
> > > > > drm_dp_mst_branch *mstb,
> > > > > }
> > > > > mutex_unlock(&mgr->qlock);
> > > > >
> > > > > - drm_dp_mst_kick_tx(mgr);
> > > > > return ret;
> > > > > }
> > > > >
> > > > > @@ -2797,11 +2794,9 @@ static void
> > > > > process_single_down_tx_qlock(struct
> > > > > drm_dp_mst_topology_mgr *mgr)
> > > > > ret = process_single_tx_qlock(mgr, txmsg, false);
> > > > > if (ret == 1) {
> > > > > /* txmsg is sent it should be in the slots now */
> > > > > - mgr->is_waiting_for_dwn_reply = true;
> > > > > list_del(&txmsg->next);
> > > > > } else if (ret) {
> > > > > DRM_DEBUG_KMS("failed to send msg in q %d\n", ret);
> > > > > - mgr->is_waiting_for_dwn_reply = false;
> > > > > list_del(&txmsg->next);
> > > > > if (txmsg->seqno != -1)
> > > > > txmsg->dst->tx_slots[txmsg->seqno] = NULL;
> > > @@
> > > > > -2841,8
> > > > > +2836,7 @@ static void drm_dp_queue_down_tx(struct
> > > > > drm_dp_mst_topology_mgr *mgr,
> > > > > drm_dp_mst_dump_sideband_msg_tx(&p, txmsg);
> > > > > }
> > > > >
> > > > > - if (list_is_singular(&mgr->tx_msg_downq) &&
> > > > > - !mgr->is_waiting_for_dwn_reply)
> > > > > + if (list_is_singular(&mgr->tx_msg_downq))
> > > > > process_single_down_tx_qlock(mgr);
> > > > > mutex_unlock(&mgr->qlock);
> > > > > }
> > > > > @@ -3822,7 +3816,6 @@ static int drm_dp_mst_handle_down_rep(struct
> > > > > drm_dp_mst_topology_mgr *mgr)
> > > > > mutex_lock(&mgr->qlock);
> > > > > txmsg->state = DRM_DP_SIDEBAND_TX_RX;
> > > > > mstb->tx_slots[seqno] = NULL;
> > > > > - mgr->is_waiting_for_dwn_reply = false;
> > > > > mutex_unlock(&mgr->qlock);
> > > > >
> > > > > wake_up_all(&mgr->tx_waitq);
> > > > > @@ -3830,9 +3823,6 @@ static int drm_dp_mst_handle_down_rep(struct
> > > > > drm_dp_mst_topology_mgr *mgr)
> > > > > return 0;
> > > > >
> > > > > out_clear_reply:
> > > > > - mutex_lock(&mgr->qlock);
> > > > > - mgr->is_waiting_for_dwn_reply = false;
> > > > > - mutex_unlock(&mgr->qlock);
> > > > > if (msg)
> > > > > memset(msg, 0, sizeof(struct
> > > drm_dp_sideband_msg_rx));
> > > > > out:
> > > > > @@ -4670,7 +4660,7 @@ static void drm_dp_tx_work(struct work_struct
> > > > > *work)
> > > > > struct drm_dp_mst_topology_mgr *mgr = container_of(work,
> > > > > struct drm_dp_mst_topology_mgr, tx_work);
> > > > >
> > > > > mutex_lock(&mgr->qlock);
> > > > > - if (!list_empty(&mgr->tx_msg_downq)
> > > > > && !mgr->is_waiting_for_dwn_reply)
> > > > > + if (!list_empty(&mgr->tx_msg_downq))
> > > > > process_single_down_tx_qlock(mgr);
> > > > > mutex_unlock(&mgr->qlock);
> > > > > }
> > > > > diff --git a/include/drm/drm_dp_mst_helper.h
> > > > > b/include/drm/drm_dp_mst_helper.h index
> > > 7d0341f94ce1b..fcc30e64c8e7e
> > > > > 100644
> > > > > --- a/include/drm/drm_dp_mst_helper.h
> > > > > +++ b/include/drm/drm_dp_mst_helper.h
> > > > > @@ -619,12 +619,6 @@ struct drm_dp_mst_topology_mgr {
> > > > > * &drm_dp_sideband_msg_tx.state once they are queued
> > > > > */
> > > > > struct mutex qlock;
> > > > > -
> > > > > - /**
> > > > > - * @is_waiting_for_dwn_reply: indicate whether is waiting for
> > > down
> > > > > reply
> > > > > - */
> > > > > - bool is_waiting_for_dwn_reply;
> > > > > -
> > > > > /**
> > > > > * @tx_msg_downq: List of pending down replies.
> > > > > */
> > > > > --
> > > > > Sean Paul, Software Engineer, Google / Chromium OS
> > > > --
> > > > Wayne Lin
> > --
> > Best regards,
> > Wayne Lin
>
> --
> Sean Paul, Software Engineer, Google / Chromium OS
--
Sean Paul, Software Engineer, Google / Chromium OS
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