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

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

On Thu, Dec 21, 2017 at 05:06:22PM -0800, Pandiyan, Dhinakaran wrote:
> 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@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?
> 
> 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 :)
>

It still appears to be a magical number so better to comment it properly.
Helps in the debug
 
> >   
> > > -	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.

Yes the variable attempts is misleading in that case. Probably call it "tries"

Manasi

> > 
> > 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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