[PATCHv2 11/22] drm/bridge: tc358767: ensure DP is disabled before LT

[Laurent Pinchart]

Hi Tomi,

On Mon, Apr 15, 2019 at 02:26:20PM +0300, Tomi Valkeinen wrote:
> On 15/04/2019 11:49, Andrzej Hajda wrote:
> > On 26.03.2019 11:31, Tomi Valkeinen wrote:
> >> Link training will sometimes fail if the DP link is, for some whatever
> >> reason, enabled when tc_main_link_enable() is called.
> > 
> > Only tc_stream_enable enables it, does it mean that link training can
> > happen after tc_stream_enable?
> > 
> > It suggests that driver/device preforms strange things, is it true? Or
> > just overprotection?
> 
> Just protection. I did try all kinds of things when trying to get the
> link setup stable and having DP0CTL enabled before link training was one
> of the problems I encountered.
> 
> In theory DP0CTL should always be disabled when we call
> tc_main_link_enable, but I thought it best leave it there in case we
> accidentally leave DP0CTL enabled via some error path or such.
> 
> Maybe we should have a WARN there if DP0CTL is enabled (and then clear
> it), so that we might find those error cases.

I'd prefer a warning, as incorrect error paths (or such) could also
create lots of other issues. I don't think we should protect against one
particular issue that is supposed never to happen and then consider that
we're safe.

-- 
Regards,

Laurent Pinchart