drm/i915/dmc: Also disable HRR event on TGL/ADLS main DMC

Unlike later platforms TGL/ADLS has the half refresh rate (HRR) event
on the main DMC (as opposed to the pipe DMC). Since we're disabling
that event on all later platforms already let's do the same on
TGL/ADLS as well.

There is supposedly a bit somewhere (DMC_CHICKEN on TGL) to make
the handler not do anything, but we don't currently have code
to frob it. Though that bit should be off by default, the ADL+
experience has shown us that trusting any of this isn't a good
idea. So seems safer to just disable all event handlers we know
that we don't need.

Also the TGL/ADLS DMC firmware is apparently using the wrong event
(undelayed vblank) here anyway. It should be using the delayed
vblank event instead (like ADL+ firmware does), but they didn't
release a firmware fix for this and instead just hacked around
this in the Windows driver code :/

v2: Also disable the event on ADLS (Imre)

Cc: Imre Deak <imre.deak@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231213150807.21331-1-ville.syrjala@linux.intel.com
Reviewed-by: Imre Deak <imre.deak@intel.com>

Author: vsyrjala

drivers/gpu/drm/i915/display/intel_dmc.c

@@ -448,6 +448,11 @@ static bool disable_dmc_evt(struct drm_i915_private *i915,
 	    REG_FIELD_GET(DMC_EVT_CTL_EVENT_ID_MASK, data) == DMC_EVT_CTL_EVENT_ID_CLK_MSEC)
 		return true;
 
+	/* also disable the HRR event on the main DMC on TGL/ADLS */
+	if ((IS_TIGERLAKE(i915) || IS_ALDERLAKE_S(i915)) &&
+	    REG_FIELD_GET(DMC_EVT_CTL_EVENT_ID_MASK, data) == DMC_EVT_CTL_EVENT_ID_VBLANK_A)
+		return true;
+
 	return false;
 }
 

drivers/gpu/drm/i915/display/intel_dmc_regs.h

@@ -60,6 +60,7 @@
 
 #define DMC_EVT_CTL_EVENT_ID_MASK	REG_GENMASK(15, 8)
 #define DMC_EVT_CTL_EVENT_ID_FALSE	0x01
+#define DMC_EVT_CTL_EVENT_ID_VBLANK_A	0x32 /* main DMC */
 /* An event handler scheduled to run at a 1 kHz frequency. */
 #define DMC_EVT_CTL_EVENT_ID_CLK_MSEC	0xbf