FAILED: patch "[PATCH] drm/i915/mst: limit DP MST ESI service loop" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-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-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 005771c18c5b2c98cb4e7517661aea460990fd3f
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026072902-erased-snuff-835e@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

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

From 005771c18c5b2c98cb4e7517661aea460990fd3f Mon Sep 17 00:00:00 2001
From: Jani Nikula <[email protected]>
Date: Thu, 25 Jun 2026 17:22:04 +0300
Subject: [PATCH] drm/i915/mst: limit DP MST ESI service loop
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

The loop in intel_dp_check_mst_status() keeps servicing interrupts originating from the sink without bound. Add an upper bound to the new interrupts occurring during interrupt processing to not get stuck on potentially stuck sink devices. Use arbitrary 32 tries to clear incoming interrupts in one go.

Discovered using AI-assisted static analysis confirmed by Intel Product Security.

Note: The condition likely pre-dates the commit in the Fixes: tag, but this is about as far back as a backport has any chance of succeeding. Before that, the retry had a goto.

index 85d3aa3b9894..7ff5712f8b19 100644
@@ -5737,8 +5737,9 @@ intel_dp_check_mst_status(struct intel_dp *intel_dp)
 	struct intel_display *display = to_intel_display(intel_dp);
 	bool force_retrain = intel_dp->link.force_retrain;
 	bool reprobe_needed = false;
+	int tries = 33;
 
-	for (;;) {
+	while (--tries) {
 		u8 esi[4] = {};
 		u8 ack[4] = {};
 		bool new_irqs;

@@ -5781,6 +5782,11 @@ intel_dp_check_mst_status(struct intel_dp *intel_dp)
 			break;
 	}
 
+	if (!tries) {
+		drm_dbg_kms(display->drm, "DPRX ESI not clearing, device may be stuck\n");
+		reprobe_needed = true;
+	}
+
 	return !reprobe_needed;
 }