[PATCH 3/3] drm/nouveau: don't dereference outp before checking it in nouveau_dp_irq

[Marek Czernohous <mczernohous@gmail.com>]

From: Marek Czernohous <marek@czernohous.de>

nouveau_dp_irq() looks the encoder up and dereferences it in the same
breath, five lines before testing it:

	struct nouveau_encoder *outp = find_encoder(connector, DCB_OUTPUT_DP);
	struct nouveau_drm *drm = nouveau_drm(outp->base.base.dev);
	...
	if (!outp)
		return;

find_encoder() walks the connector's possible encoders and returns NULL
when none of them matches the requested type, so the NULL test is not
decoration: it is the author saying this can happen. The initialiser
above it dereferences the same pointer regardless.

The NULL test predates the dereference. commit 773eb04d14a1
("drm/nouveau/disp: expose conn event class") turned nouveau_dp_irq()
into a work callback, and since the drm pointer was no longer passed in
as an argument it was recovered from the encoder in the declaration
block, which put the dereference above the existing test.

Move the drm lookup below the test. No functional change when outp is
non-NULL.

Fixes: 773eb04d14a1 ("drm/nouveau/disp: expose conn event class")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-5
Signed-off-by: Marek Czernohous <marek@czernohous.de>
---
 drivers/gpu/drm/nouveau/nouveau_dp.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_dp.c b/drivers/gpu/drm/nouveau/nouveau_dp.c
index 55691ec44aba..738802358d85 100644
--- a/drivers/gpu/drm/nouveau/nouveau_dp.c
+++ b/drivers/gpu/drm/nouveau/nouveau_dp.c
@@ -486,7 +486,7 @@ nouveau_dp_irq(struct work_struct *work)
 		container_of(work, typeof(*nv_connector), irq_work);
 	struct drm_connector *connector = &nv_connector->base;
 	struct nouveau_encoder *outp = find_encoder(connector, DCB_OUTPUT_DP);
-	struct nouveau_drm *drm = nouveau_drm(outp->base.base.dev);
+	struct nouveau_drm *drm;
 	struct nv50_mstm *mstm;
 	u64 hpd = 0;
 	int ret;
@@ -494,6 +494,8 @@ nouveau_dp_irq(struct work_struct *work)
 	if (!outp)
 		return;
 
+	drm = nouveau_drm(outp->base.base.dev);
+
 	mstm = outp->dp.mstm;
 	NV_DEBUG(drm, "service %s\n", connector->name);
 
-- 
2.54.0