[PATCH] drm/dp_mst: Tune down the WARN modesetting a port with full_pbn=0

[Lyude Paul]

On Tue, 2021-02-16 at 14:34 +0200, Imre Deak wrote:
> It's possible to modeset a connector/mst port that has a 0 full_pbn
> value: if the sink on the port deasserts its HPD and a branch device
> reports this via a CSN with the port's ddps=0 and pdt!=NONE the driver
> clears full_pbn, but the corresponding connector can be still
> modesetted.
> 
> This happened on a DELL U2719D monitor as the branch device and an LG
> 27UL650-W daisy-chained to it, the LG monitor generating a long HPD
> pulse (doing this for some reason always when waking up from some power
> saving state).
> 
> Tune down the WARN about this scenario to a debug message.
> 
> References: https://gitlab.freedesktop.org/drm/intel/-/issues/1917
> Cc: Lyude Paul <lyude at redhat.com>
> Signed-off-by: Imre Deak <imre.deak at intel.com>
> ---
>  drivers/gpu/drm/drm_dp_mst_topology.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> b/drivers/gpu/drm/drm_dp_mst_topology.c
> index 0a54506c27738..dcaf4bf9b62f6 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -5118,11 +5118,15 @@ drm_dp_mst_atomic_check_port_bw_limit(struct
> drm_dp_mst_port *port,
>                 if (!found)
>                         return 0;
>  
> -               /* This should never happen, as it means we tried to
> -                * set a mode before querying the full_pbn
> +               /*
> +                * This could happen if the sink deasserted its HPD line, but
> +                * the branch device still reports it as attached (PDT !=
> NONE).
>                  */
> -               if (WARN_ON(!port->full_pbn))
> +               if (!port->full_pbn) {
> +                       drm_dbg_kms(port->mgr->dev, "[MSTB:%p] [MST PORT:%p]
> no BW available for the port\n",
> +                                   port->parent, port);

Shouldn't this use the atomic debugging level? With that fixed, this is:

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

>                         return -EINVAL;
> +               }
>  
>                 pbn_used = vcpi->pbn;
>         } else {

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