[Intel-gfx] [PATCH] drm/i915/hotplug: Reduce SHPD_FILTER to 250us

[Kandpal, Suraj]

> 
> > -----Original Message-----
> > From: Kandpal, Suraj <suraj.kandpal at intel.com>
> > Sent: Monday, July 17, 2023 2:54 PM
> > To: intel-gfx at lists.freedesktop.org
> > Cc: Kandpal, Suraj <suraj.kandpal at intel.com>; Shankar, Uma
> > <uma.shankar at intel.com>; Ville Syrjala <ville.syrjala at linux.intel.com>
> > Subject: [PATCH] drm/i915/hotplug: Reduce SHPD_FILTER to 250us
> >
> > On TGP, the RTC (always running) was reduced from 3MHz to 32KHz.
> > As a result of this change, when HPD active going low pulse or HPD IRQ
> > is presented and the refclk (19.2MHz) is not toggling already
> > toggling, there is a 60 to 90us synchronization delay which
> > effectively reduces the duration of the IRQ pulse to less than the
> programmed 500us filter value and the hot plug interrupt is NOT registered.
> > Solution was to Reduce SHPD_FILTER to 250us for ADL and above.
> > This solution was derived when the below patch was floated.
> > [1]https://patchwork.freedesktop.org/patch/532187
> > and after some internal discussion Ville's suggestion made sense.
> 
> Looks Good to me. Just add also a Suggested-By tag mentioning Ville.
> Reviewed-by: Uma Shankar <uma.shankar at intel.com>
> 

Sure Uma will do, can you also help with getting this merged

Regards,
Suraj Kandpal
> > Bspec: 68970
> >
> > Cc: Uma Shankar <uma.shankar at intel.com>
> > Cc: Ville Syrjala <ville.syrjala at linux.intel.com>
> > Signed-off-by: Suraj Kandpal <suraj.kandpal at intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_hotplug_irq.c | 4 +++-
> >  drivers/gpu/drm/i915/i915_reg.h                  | 1 +
> >  2 files changed, 4 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 f95fa793fabb..95a7ea94f417 100644
> > --- a/drivers/gpu/drm/i915/display/intel_hotplug_irq.c
> > +++ b/drivers/gpu/drm/i915/display/intel_hotplug_irq.c
> > @@ -842,6 +842,8 @@ static void icp_hpd_irq_setup(struct
> > drm_i915_private
> > *dev_priv)
> >
> >  	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);
> >
> >  	ibx_display_interrupt_update(dev_priv, hotplug_irqs, enabled_irqs);
> >
> > @@ -1049,7 +1051,7 @@ static void mtp_hpd_irq_setup(struct
> > drm_i915_private
> > *i915)
> >  	enabled_irqs = intel_hpd_enabled_irqs(i915, i915-
> >display.hotplug.pch_hpd);
> >  	hotplug_irqs = intel_hpd_hotplug_irqs(i915,
> > i915->display.hotplug.pch_hpd);
> >
> > -	intel_de_write(i915, SHPD_FILTER_CNT,
> SHPD_FILTER_CNT_500_ADJ);
> > +	intel_de_write(i915, SHPD_FILTER_CNT, SHPD_FILTER_CNT_250);
> >
> >  	mtp_hpd_invert(i915);
> >  	ibx_display_interrupt_update(i915, hotplug_irqs, enabled_irqs); diff
> > --git a/drivers/gpu/drm/i915/i915_reg.h
> > b/drivers/gpu/drm/i915/i915_reg.h index dcf64e32cd54..aefad14ab27a
> > 100644
> > --- a/drivers/gpu/drm/i915/i915_reg.h
> > +++ b/drivers/gpu/drm/i915/i915_reg.h
> > @@ -4939,6 +4939,7 @@
> >
> >  #define SHPD_FILTER_CNT				_MMIO(0xc4038)
> >  #define   SHPD_FILTER_CNT_500_ADJ		0x001D9
> > +#define   SHPD_FILTER_CNT_250			0x000F8
> >
> >  #define _PCH_DPLL_A              0xc6014
> >  #define _PCH_DPLL_B              0xc6018
> > --
> > 2.25.1