Re: [PATCH] drm/dp: Power cycle display if LINK_ADDRESS fails.

[Lyude Paul <lyude@redhat.com>]

Sorry for the late reply, I've been having very similar issues on my own MST hub
and I wanted to make sure that they were the same issue, although it seems like
they aren't.

So; I've been doing a lot of MST debugging this week and last and something I've
discovered needs to be taken into account sometimes with MST hubs is the actual
state that they're in at the point that the DRM driver detects them. I've
managed to on multiple occasions, get my hub into a weird state by:

- Plugging in MST displays into the hub
- Turning on the machine
- Unplugging MST displays from the hub (while still in the BIOS)
- Booting into linux
- Plugging MST displays into the hub
- Everything times out, the world explodes, the economy collapses, etc.

I think maybe, especially since this should be perfectly valid behavior and not
break well or poor behaving hubs, we should do a power cycle with the display
like this when the DP port initially detects an MST hub and before we start
doing any serious communication with it. Could you see if this fixes your issue
instead of the patch you've got here?

As well, mind attaching your full dmesg with drm.debug=0x6?

On Wed, 2017-12-20 at 22:36 -0800, Dhinakaran Pandiyan wrote:
> Occasionally there are LINK_ADDRESS sideband messages timing out with the
> Lenovo MST dock + Dell MST monitor(w/ in-built branch) setup I have. These
> failures lead to the display not coming up on boot. Power cycling the port
> corresponding to the MST monitor's branch device and resending the message
> fixes the issue. I am not entirely sure if this is specific to my setup.
> However, as the power state is toggled conditionally on LINK_ADDRESS
> timeouts, this should not affect the working cases.
> 
> Cc: Lyude <lyude@redhat.com>
> Cc: Dave Airlie <airlied@redhat.com>
> Cc: Jani Nikula <jani.nikula@intel.com>
> Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
> ---
>  drivers/gpu/drm/drm_dp_mst_topology.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> b/drivers/gpu/drm/drm_dp_mst_topology.c
> index 70dcfa58d3c2..e06defcdcf18 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -1596,8 +1596,9 @@ static void drm_dp_send_link_address(struct
> drm_dp_mst_topology_mgr *mgr,
>  	int len;
>  	struct drm_dp_sideband_msg_tx *txmsg;
>  	int ret;
> +	int attempts = 5;
>  
> -	txmsg = kzalloc(sizeof(*txmsg), GFP_KERNEL);
> +retry:	txmsg = kzalloc(sizeof(*txmsg), GFP_KERNEL);
>  	if (!txmsg)
>  		return;
>  
> @@ -1635,9 +1636,17 @@ static void drm_dp_send_link_address(struct
> drm_dp_mst_topology_mgr *mgr,
>  			}
>  			(*mgr->cbs->hotplug)(mgr);
>  		}
> +	} else if (attempts--) {
> +		kfree(txmsg);
> +		drm_dp_send_power_updown_phy(mstb->mgr, mstb->port_parent,
> +					     false);
> +		drm_dp_send_power_updown_phy(mstb->mgr, mstb->port_parent,
> +					     true);
> +		DRM_DEBUG_KMS("link address failed %d, retrying\n", ret);
> +		goto retry;
>  	} else {
>  		mstb->link_address_sent = false;
> -		DRM_DEBUG_KMS("link address failed %d\n", ret);
> +		DRM_DEBUG_KMS("link address failed %d, giving up\n", ret);
>  	}
>  
>  	kfree(txmsg);
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