[PATCH] drm/dp_mst: Lower down debug info level when receive NAK

[Lin, Wayne]

[Public]

Thank you Lyude!

Regards,
Wayne
________________________________________
From: Lyude Paul <lyude at redhat.com>
Sent: Friday, April 29, 2022 00:45
To: Lin, Wayne; dri-devel at lists.freedesktop.org
Cc: ville.syrjala at linux.intel.com; Wentland, Harry; Zuo, Jerry; Siqueira, Rodrigo
Subject: Re: [PATCH] drm/dp_mst: Lower down debug info level when receive NAK

Reviewed-by: Lyude Paul <lyude at redhat.com>

Will push to drm-misc-next in a bit

On Thu, 2022-04-28 at 20:49 +0800, Wayne Lin wrote:
> [Why]
> It's reasonable that we receive NAK while doing DP_REMOTE_DPCD_READ.
> Downstream device might reply NAK with the reason and source should
> react accordingly.
>
> e.g.
> 1. When downstream device can't handle corresponding message in time,
> it then replies NAK as reason been set as DEFER.
> 2. When multi-function branch-sink device doesn't enumerate virtual
> DP peer devices for those multi-function down facing ports. Without
> virtual DPCD, branch device might reply NAK with reason as BAD_PARAM
> indicating this port can't do aux DPCD read.
>
> It's expected result. Not an error.
>
> [How]
> Use drm_dbg_kms() to replace drm_err() when receive NAK.
>
> Changes since v1:
> * drm_dp_mst_topology.c file path changed. Folder was rename from
>  'dp' to 'display'
>
> Signed-off-by: Wayne Lin <Wayne.Lin at amd.com>
> Reviewed-by: Harry Wentland <harry.wentland at amd.com>
> ---
>  drivers/gpu/drm/display/drm_dp_mst_topology.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c
> b/drivers/gpu/drm/display/drm_dp_mst_topology.c
> index 8526aae75c6d..f27aa0b95bea 100644
> --- a/drivers/gpu/drm/display/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c
> @@ -3557,9 +3557,8 @@ static int drm_dp_send_dpcd_read(struct
> drm_dp_mst_topology_mgr *mgr,
>         if (ret < 0)
>                 goto fail_free;
>
> -       /* DPCD read should never be NACKed */
>         if (txmsg->reply.reply_type == 1) {
> -               drm_err(mgr->dev, "mstb %p port %d: DPCD read on addr 0x%x
> for %d bytes NAKed\n",
> +               drm_dbg_kms(mgr->dev, "mstb %p port %d: DPCD read on addr
> 0x%x for %d bytes NAKed\n",
>                         mstb, port->port_num, offset, size);
>                 ret = -EIO;
>                 goto fail_free;

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