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

[Manasi Navare <manasi.d.navare@intel.com>]

On Wed, Dec 20, 2017 at 10:36:24PM -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;
>

Does the spec say this should be retried 5 times or is this just an
experimental number?
We have such magical numbers for retries all over the DP code and that makes debugging
harder later, so atleast a comment of why its 5 would help.
  
> -	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--) {

This should be --attempts if you want the total attempts to be 5

Manasi

> +		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);
> -- 
> 2.11.0
> 
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