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Date:   Thu, 22 Jul 2021 13:53:34 -0400
From:   Lyude Paul <lyude@...hat.com>
To:     khsieh@...eaurora.org, Jani Nikula <jani.nikula@...ux.intel.com>
Cc:     robdclark@...il.com, sean@...rly.run, swboyd@...omium.org,
        abhinavk@...eaurora.org, aravindh@...eaurora.org,
        rsubbia@...eaurora.org, rnayak@...eaurora.org,
        freedreno@...ts.freedesktop.org, airlied@...ux.ie, daniel@...ll.ch,
        maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
        tzimmermann@...e.de, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] drm/dp_mst: Fix return code on sideband message
 failure

On Tue, 2021-07-13 at 15:24 -0700, khsieh@...eaurora.org wrote:
> On 2021-07-07 01:37, Jani Nikula wrote:
> > On Tue, 06 Jul 2021, Kuogee Hsieh <khsieh@...eaurora.org> wrote:
> > > From: Rajkumar Subbiah <rsubbia@...eaurora.org>
> > > 
> > > Commit 2f015ec6eab6 ("drm/dp_mst: Add sideband down request tracing +
> > > selftests") added some debug code for sideband message tracing. But
> > > it seems to have unintentionally changed the behavior on sideband 
> > > message
> > > failure. It catches and returns failure only if DRM_UT_DP is enabled.
> > > Otherwise it ignores the error code and returns success. So on an MST
> > > unplug, the caller is unaware that the clear payload message failed 
> > > and
> > > ends up waiting for 4 seconds for the response. Fixes the issue by
> > > returning the proper error code.
> > > 
> > > Changes in V2:
> > > -- Revise commit text as review comment
> > > -- add Fixes text
> > > 
> > > Changes in V3:
> > > -- remove "unlikely" optimization
> > > 
> > > Fixes: 2f015ec6eab6 ("drm/dp_mst: Add sideband down request tracing + 
> > > selftests")
> > > 
> > > Signed-off-by: Rajkumar Subbiah <rsubbia@...eaurora.org>
> > > Signed-off-by: Kuogee Hsieh <khsieh@...eaurora.org>
> > > 
> > > Reviewed-by: Stephen Boyd <swboyd@...omium.org>
> > 
> > Reviewed-by: Jani Nikula <jani.nikula@...el.com>
> > 
> > 
> > > ---
> Lyude,
> Any comments from you?
> Thanks,

Hey! Sorry did I forget to respond to this?

Reviewed-by: Lyude Paul <lyude@...hat.com>

> 
> > >  drivers/gpu/drm/drm_dp_mst_topology.c | 10 ++++++----
> > >  1 file changed, 6 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c 
> > > b/drivers/gpu/drm/drm_dp_mst_topology.c
> > > index 1590144..df91110 100644
> > > --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> > > +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> > > @@ -2887,11 +2887,13 @@ static int process_single_tx_qlock(struct 
> > > drm_dp_mst_topology_mgr *mgr,
> > >         idx += tosend + 1;
> > > 
> > >         ret = drm_dp_send_sideband_msg(mgr, up, chunk, idx);
> > > -       if (unlikely(ret) && drm_debug_enabled(DRM_UT_DP)) {
> > > -               struct drm_printer p = drm_debug_printer(DBG_PREFIX);
> > > +       if (ret) {
> > > +               if (drm_debug_enabled(DRM_UT_DP)) {
> > > +                       struct drm_printer p =
> > > drm_debug_printer(DBG_PREFIX);
> > > 
> > > -               drm_printf(&p, "sideband msg failed to send\n");
> > > -               drm_dp_mst_dump_sideband_msg_tx(&p, txmsg);
> > > +                       drm_printf(&p, "sideband msg failed to send\n");
> > > +                       drm_dp_mst_dump_sideband_msg_tx(&p, txmsg);
> > > +               }
> > >                 return ret;
> > >         }
> 

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

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