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

[Shankar, Uma]

> -----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>

> 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