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@xxxxxxxxxx>
> > > Cc: Dave Airlie <airlied@xxxxxxxxxx>
> > > Cc: Jani Nikula <jani.nikula@xxxxxxxxx>
> > > Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@xxxxxxxxx>
> > > ---
> > > 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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