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

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

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@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.

-- 
Ville Syrjälä
Intel