[PATCH v3 3/4] drm/nouveau/fifo/nv04: filter benign CACHE_ERROR from Mesa NV50 bind probe

[Marek Czernohous <mczernohous@gmail.com>]

From: Marek Czernohous <marek@czernohous.de>

The Mesa userspace driver issues a method-0x0060 / data-0xbeef02xx
binding probe that ends up triggering CACHE_ERROR in the PFIFO
interrupt handler. The probe is harmless and recovers cleanly, but it
is reported at error level, so it shows up in dmesg on session start.

Filter that specific pattern down to debug level so dmesg stays clean
while real CACHE_ERROR conditions are still logged at error level.

The test is on the method and data pattern alone, not on the chip
family, so it applies wherever nv04_fifo_intr() is the handler, that is
nv04 through g98. That is deliberate rather than an oversight: a false
positive would need userspace to write exactly 0xbeef02xx to method
0x0060, and the probe itself comes from the shared nouveau Gallium code
rather than from anything NV50 specific. Say so here so the narrower
wording of the subject is not read as a chip gate.

Evidence: 99 occurrences across three logs from a second, independent
MCP79/MCP7A machine running 7.0.10 and 6.12.90, under both Xorg and
Wayland, with kwin and plasmashell named as the faulting clients. On my
own reference machine the filter went in before the persistent kernel
log did, so I cannot show a clean before and after from there.

Assisted-by: Claude:claude-opus-5
Signed-off-by: Marek Czernohous <marek@czernohous.de>
---
 .../gpu/drm/nouveau/nvkm/engine/fifo/nv04.c   | 26 ++++++++++++++-----
 1 file changed, 20 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nvkm/engine/fifo/nv04.c b/drivers/gpu/drm/nouveau/nvkm/engine/fifo/nv04.c
index c4b8e567d86f..ab144c1bd9da 100644
--- a/drivers/gpu/drm/nouveau/nvkm/engine/fifo/nv04.c
+++ b/drivers/gpu/drm/nouveau/nvkm/engine/fifo/nv04.c
@@ -327,12 +327,26 @@ nv04_fifo_intr_cache_error(struct nvkm_fifo *fifo, u32 chid, u32 get)
 
 	if (!(pull0 & 0x00000100) ||
 	    !nv04_fifo_swmthd(device, chid, mthd, data)) {
-		chan = nvkm_chan_get_chid(&fifo->engine, chid, &flags);
-		nvkm_error(subdev, "CACHE_ERROR - "
-			   "ch %d [%s] subc %d mthd %04x data %08x\n",
-			   chid, chan ? chan->name : "unknown",
-			   (mthd >> 13) & 7, mthd & 0x1ffc, data);
-		nvkm_chan_put(&chan, flags);
+		/*
+		 * Filter the benign Mesa bind probe: mthd 0x0060 with data
+		 * 0xbeef02xx is a harmless userspace probe and does not
+		 * indicate an actual error condition. The test is on the
+		 * method and data pattern alone, so it applies on every
+		 * chip that reaches this handler, not just on Tesla.
+		 * Demote to debug to keep dmesg clean while still catching
+		 * real CACHE_ERROR events.
+		 */
+		if ((mthd & 0x1ffc) == 0x0060 &&
+		    (data & 0xffffff00) == 0xbeef0200) {
+			nvkm_debug(subdev, "CACHE_ERROR - ch %d subc %d mthd %04x data %08x (benign, skipped)\n",
+				   chid, (mthd >> 13) & 7, mthd & 0x1ffc, data);
+		} else {
+			chan = nvkm_chan_get_chid(&fifo->engine, chid, &flags);
+			nvkm_error(subdev, "CACHE_ERROR - ch %d [%s] subc %d mthd %04x data %08x\n",
+				   chid, chan ? chan->name : "unknown",
+				   (mthd >> 13) & 7, mthd & 0x1ffc, data);
+			nvkm_chan_put(&chan, flags);
+		}
 	}
 
 	nvkm_wr32(device, NV04_PFIFO_CACHE1_DMA_PUSH, 0);
-- 
2.54.0