drm/i915/hotplug: Add comment for XE_LPD+ SHPD_FILTER_CNT value

Add the reason for having SHPD_FILTER_CNT value for XE_LPD+ and
above as 250us instead of 500us.

--v2
-Update commit message [Matt]

Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240923031007.1058072-4-suraj.kandpal@intel.com

diff --git a/drivers/gpu/drm/i915/display/intel_hotplug_irq.c b/drivers/gpu/drm/i915/display/intel_hotplug_irq.c
index 3a105cf..5d055dc 100644 (file)
--- a/drivers/gpu/drm/i915/display/intel_hotplug_irq.c
+++ b/drivers/gpu/drm/i915/display/intel_hotplug_irq.c
@@ -1061,6 +1061,10 @@ 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);
 
+       /*
+        * Use 250us here to align with the DP1.4a(Table 3-4) spec as to what the
+        * SHPD_FILTER_CNT value should be.
+        */
        intel_de_write(i915, SHPD_FILTER_CNT, SHPD_FILTER_CNT_250);
 
        mtp_hpd_invert(i915);