[Intel-gfx] [PATCH] drm/dp: Power cycle display if LINK_ADDRESS fails.

[Pandiyan, Dhinakaran]

On Thu, 2017-12-21 at 10:52 -0800, Manasi Navare wrote:
> 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 at redhat.com>
> > Cc: Dave Airlie <airlied at redhat.com>
> > Cc: Jani Nikula <jani.nikula at intel.com>
> > Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan at 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?

The spec. does not say how many times to retry, but it does say the
source is responsible for retrying. 

> 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.

Takes about 22 seconds from boot to complete 5 retries on my SKL, I
think that's enough trying from the kernel side before pulling out the
DP cable makes sense :)

>   
> > -	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
I don't.
> 
> 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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> > dri-devel at lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
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