[PATCH 1/2] drm/i915/hotplug: Reduce SHPD_FLITER_CNT for DISPLAY_VER() == 12

[Ville Syrjälä]

On Mon, Sep 23, 2024 at 08:38:35PM +0300, Ville Syrjälä wrote:
> On Mon, Sep 23, 2024 at 08:40:07AM +0530, Suraj Kandpal wrote:
> > Reduce SHPD_CNT to 250us for display version 12 as it lines up
> > with DP1.4a(Table3-4) spec.
> > 
> > --v2
> > -Update commit message and comment [Matt]
> > 
> > Signed-off-by: Suraj Kandpal <suraj.kandpal at intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_hotplug_irq.c | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_hotplug_irq.c b/drivers/gpu/drm/i915/display/intel_hotplug_irq.c
> > index 2c4e946d5575..8427386132e6 100644
> > --- a/drivers/gpu/drm/i915/display/intel_hotplug_irq.c
> > +++ b/drivers/gpu/drm/i915/display/intel_hotplug_irq.c
> > @@ -849,7 +849,11 @@ static void icp_hpd_irq_setup(struct drm_i915_private *dev_priv)
> >  	enabled_irqs = intel_hpd_enabled_irqs(dev_priv, dev_priv->display.hotplug.pch_hpd);
> >  	hotplug_irqs = intel_hpd_hotplug_irqs(dev_priv, dev_priv->display.hotplug.pch_hpd);
> >  
> > -	if (INTEL_PCH_TYPE(dev_priv) <= PCH_TGP)
> > +	/*
> > +	 * We reduce the value to 250us to be able to detect SHPD when an external display
> > +	 * is connected. This is also expected of us as stated in DP1.4a Table 3-4.
> > +	 */
> > +	if (INTEL_PCH_TYPE(dev_priv) < PCH_TGP)
> >  		intel_uncore_write(&dev_priv->uncore, SHPD_FILTER_CNT, SHPD_FILTER_CNT_500_ADJ);
> >  	else
> >  		intel_uncore_write(&dev_priv->uncore, SHPD_FILTER_CNT, SHPD_FILTER_CNT_250);
> 
> IMO if we start reducing this for older platforms then we
> should just do it for all of them, instead of based on some
> random cutoff.

The other things we might want to think about are moving this
into *_hpd_detection_setup() instead, and perhaps we should
also start explicitly configuring SHPD_PULSE_CNT as well?

-- 
Ville Syrjälä
Intel