[Intel-gfx] [PATCH] drm/i915: Fix the HDMI hot plug disconnection failure (v4)

[Guang Bai]

On Thu, 29 Nov 2018 10:17:49 +0200
Jani Nikula <jani.nikula at intel.com> wrote:

> On Wed, 28 Nov 2018, Guang Bai <guang.bai at intel.com> wrote:
> > On some GEN9 platforms, slowly unplugging (wiggling) the HDMI cable
> > makes the kernel to believe the HDMI display is still connected.
> > This is because the HDMI DDC lines are disconnected a little bit
> > later after the hot-plug interrupt triggered thus an immediate edid
> > fetch can be made. This problem has been identified by more than
> > one customer recently. Use digital port live states to authorize
> > the edid read at HDMI detection point will ensure most of the
> > display related software states updated and rest of them will be
> > renewed accordingly when the port is connected.
> >
> > v2: Fix the formatting issue
> > v3: Use digital port states to authorize the edid read
> > v4: Add comments on issue histories and rationale of the fix (Chris
> > W)  
> 
> You're not answering Chris Wilson's question.
> 
> Why do you think the problems we've historically had with live status
> are no longer a problem? We've tried and reverted live status checks
> at least twice before because of regressions. Why do you think this
> time there won't be regressions? Why do you think this patch makes
> forward progress?
Jani,
I'm still new to kernel developments compared with all of you working
in this area for many years - Haven't got any feedbacks on how
exactly the HDMI live statue *not* fit for HDMI hot-plug related port
status checking, neither had time to track all upstream bugzilla, plus
not working directly with Intel OTC teams
- What are those failing cases/regressions you mentioned above?
- what were the kernel versions related with those developments?
- Given the fact i915 architecture and implementation are constantly
  evolving - Should we re-visit those issues with current kernel
  implementation?
- Fundamentally, do you think the edid fetch is still *valid* when the
  HDMI is unplugged (status either from PCH or DE)? Or other platform
  configurations may present more complexities such as kvm switches are
  used along with HDMI?
Again, if you could provide me more historical issue details, I'd like
to have some reviews/re-investigation for those cases with current 4.20
kernel.
Thanks,
-Guang
> 
> I've *repeatedly* said from the beginning that I am very sceptical of
> using live status because we've been burned by it so many times
> before. I don't much care to repeat this anymore.
> 
> 
> BR,
> Jani.
> 
> 
> >
> > Cc: Jani Nikula <jani.nikula at intel.com>
> > Cc: Chris Chiu <chiu at endlessm.com>
> > Cc: Chris Wilson <chris at chris-wilson.co.uk>
> > Signed-off-by: Guang Bai <guang.bai at intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_hdmi.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_hdmi.c
> > b/drivers/gpu/drm/i915/intel_hdmi.c index e2c6a2b..8cf7c78 100644
> > --- a/drivers/gpu/drm/i915/intel_hdmi.c
> > +++ b/drivers/gpu/drm/i915/intel_hdmi.c
> > @@ -1929,7 +1929,7 @@ intel_hdmi_detect(struct drm_connector
> > *connector, bool force) 
> >  	intel_display_power_get(dev_priv, POWER_DOMAIN_GMBUS);
> >  
> > -	if (IS_ICELAKE(dev_priv) &&
> > +	if ((IS_ICELAKE(dev_priv) || IS_GEN9_BC(dev_priv)) &&
> >  	    !intel_digital_port_connected(encoder))
> >  		goto out;  
>