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

[Stephen Boyd]

+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 at codeaurora.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 at codeaurora.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 at chromium.org>