Re: [PATCH v2] drm/dp_mst: Fix return code on sideband message failure

[Lyude Paul]

JFYI: will try to take a look at this at the start of next week

On Tue, 2021-06-29 at 16:07 -0700, Kuogee Hsieh wrote:
> From: Rajkumar Subbiah <rsubbia@xxxxxxxxxxxxxx>
> 
> 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
> 
> Fixes: 2f015ec6eab6 ("drm/dp_mst: Add sideband down request tracing +
> selftests")
> 
> Signed-off-by: Rajkumar Subbiah <rsubbia@xxxxxxxxxxxxxx>
> Signed-off-by: Kuogee Hsieh <khsieh@xxxxxxxxxxxxxx>
> 
> Reviewed-by: Stephen Boyd <swboyd@xxxxxxxxxxxx>
> ---
>  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;
>         }
>  

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