On 2022-03-29 04:05, 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.
>
> Signed-off-by: Wayne Lin <wayne....@amd.com>
Reviewed-by: Harry Wentland <harry.wentl...@amd.com>
Harry
> ---
> drivers/gpu/drm/dp/drm_dp_mst_topology.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/dp/drm_dp_mst_topology.c
> b/drivers/gpu/drm/dp/drm_dp_mst_topology.c
> index 11300b53d24f..764a6b59bc1e 100644
> --- a/drivers/gpu/drm/dp/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/dp/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;
