linux-kernel - Re: [PATCH] drm/dp_mst: Fix return code on sideband message failure

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Date:   Tue, 29 Jun 2021 17:38:17 -0400
From:   Lyude Paul <lyude@...hat.com>
To:     Stephen Boyd <swboyd@...omium.org>,
        Kuogee Hsieh <khsieh@...eaurora.org>, robdclark@...il.com,
        sean@...rly.run
Cc:     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] drm/dp_mst: Fix return code on sideband message failure

JFYI this is on my radar and I'll take a look asap

On Tue, 2021-06-29 at 13:41 -0700, Stephen Boyd wrote:
> +Lyude, author of fixed commit. Please add relevant folks in the future.
> 
> Quoting Kuogee Hsieh (2021-06-29 13:08:56)
> > From: Rajkumar Subbiah <rsubbia@...eaurora.org>
> > 
> > The commit 2f015ec6eab69301fdcf54d397810d72362d7223 added some debug
> 
> Please write
> 
> 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.
> > 
> > This change fixes the issue by returning the proper error code.
> 
> $ git grep "This patch" -- Documentation/process
> 
> > 
> > Change-Id: I2887b7ca21355fe84a7968f7619d5e8199cbb0c6
> 
> Please replace with
> 
> Fixes: 2f015ec6eab6 ("drm/dp_mst: Add sideband down request tracing +
> selftests")
> 
> > Signed-off-by: Rajkumar Subbiah <rsubbia@...eaurora.org>
> 
> Should be a Signed-off-by from Kuogee Hsieh here.
> 
> > ---
> >  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..8d97430 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 (unlikely(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;
> >         }
> > 
> 
> With the above fixed up
> 
> Reviewed-by: Stephen Boyd <swboyd@...omium.org>
> 

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