FAILED: patch "[PATCH] drm/i915/psr: Only allow PSR in LPSP mode on HSW non-ULT" failed to apply to 6.6-stable tree

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x f9f031dd21a7ce13a13862fa5281d32e1029c70f
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2024012730-encroach-lid-4960@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:

f9f031dd21a7 ("drm/i915/psr: Only allow PSR in LPSP mode on HSW non-ULT") a2cd15c24116 ("drm/i915/lnl: Remove watchdog timers for PSR")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From f9f031dd21a7ce13a13862fa5281d32e1029c70f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ville=20Syrj=C3=A4l=C3=A4?= <[email protected]>
Date: Thu, 18 Jan 2024 23:21:31 +0200
Subject: [PATCH] drm/i915/psr: Only allow PSR in LPSP mode on HSW non-ULT
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On HSW non-ULT (or at least on Dell Latitude E6540) external displays start to flicker when we enable PSR on the eDP. We observe a much higher SR and PC6 residency than should be possible with an external display, and indeen much higher than what we observe with eDP disabled and only the external display enabled. Looks like the hardware is somehow ignoring the fact that the external display is active during PSR.

I wasn't able to redproduce this on my HSW ULT machine, or BDW. So either there's something specific about this particular laptop (eg. some unknown firmware thing) or the issue is limited to just non-ULT HSW systems. All known registers that could affect this look perfectly reasonable on the affected machine.

As a workaround let's unmask the LPSP event to prevent PSR entry except while in LPSP mode (only pipe A + eDP active). This will prevent PSR entry entirely when multiple pipes are active. The one slight downside is that we now also prevent PSR entry when driving eDP with pipe B or C, but I think that's a reasonable tradeoff to avoid having to implement a more complex workaround.

index 8f702c3fc62d..57bbf3e3af92 100644
@@ -1525,8 +1525,18 @@ static void intel_psr_enable_source(struct intel_dp *intel_dp,
 	 * can rely on frontbuffer tracking.
 	 */
 	mask = EDP_PSR_DEBUG_MASK_MEMUP |
-	       EDP_PSR_DEBUG_MASK_HPD |
-	       EDP_PSR_DEBUG_MASK_LPSP;
+	       EDP_PSR_DEBUG_MASK_HPD;
+
+	/*
+	 * For some unknown reason on HSW non-ULT (or at least on
+	 * Dell Latitude E6540) external displays start to flicker
+	 * when PSR is enabled on the eDP. SR/PC6 residency is much
+	 * higher than should be possible with an external display.
+	 * As a workaround leave LPSP unmasked to prevent PSR entry
+	 * when external displays are active.
+	 */
+	if (DISPLAY_VER(dev_priv) >= 8 || IS_HASWELL_ULT(dev_priv))
+		mask |= EDP_PSR_DEBUG_MASK_LPSP;
 
 	if (DISPLAY_VER(dev_priv) < 20)
 		mask |= EDP_PSR_DEBUG_MASK_MAX_SLEEP;