linux-kernel - Re: [PATCH 4/4] drm/dp_mst: Print errors on ACT timeouts

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Date:   Mon, 6 Apr 2020 15:43:06 -0400
From:   Sean Paul <sean@...rly.run>
To:     Lyude Paul <lyude@...hat.com>
Cc:     dri-devel <dri-devel@...ts.freedesktop.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/4] drm/dp_mst: Print errors on ACT timeouts

On Fri, Apr 3, 2020 at 4:08 PM Lyude Paul <lyude@...hat.com> wrote:
>
> Although it's not unexpected for drm_dp_check_act_status() to fail due
> to DPCD read failures (as the hub may have just been unplugged
> suddenly), timeouts are a bit more worrying as they either mean we need
> a longer timeout value, or we aren't setting up payload allocations
> properly. So, let's start printing errors on timeouts.
>
> Signed-off-by: Lyude Paul <lyude@...hat.com>
> Cc: Sean Paul <sean@...rly.run>

Reviewed-by: Sean Paul <sean@...rly.run>

> ---
>  drivers/gpu/drm/drm_dp_mst_topology.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
> index f313407374ed..3d0d373f6f91 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -4494,6 +4494,10 @@ int drm_dp_check_act_status(struct drm_dp_mst_topology_mgr *mgr)
>                                         DP_PAYLOAD_TABLE_UPDATE_STATUS,
>                                         &status);
>                 if (ret < 0) {
> +                       /*
> +                        * Failure here isn't unexpected - the hub may have
> +                        * just been unplugged
> +                        */
>                         DRM_DEBUG_KMS("failed to read payload table status %d\n",
>                                       ret);
>                         return ret;
> @@ -4505,8 +4509,8 @@ int drm_dp_check_act_status(struct drm_dp_mst_topology_mgr *mgr)
>         } while (jiffies < timeout);
>
>         if (!(status & DP_PAYLOAD_ACT_HANDLED)) {
> -               DRM_DEBUG_KMS("failed to get ACT bit %d after %dms\n",
> -                             status, timeout_ms);
> +               DRM_ERROR("Failed to get ACT after %dms, last status: %02x\n",
> +                         timeout_ms, status);
>                 return -EINVAL;
>         }
>         return 0;
> --
> 2.25.1
>