linux-kernel - [PATCH v3 5/5] drm/msm/dpu: rate limit snapshot capture for mmu faults

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Message-ID: <20250219-abhinavk-smmu-fault-handler-v3-5-aa3f0bf4434a@quicinc.com>
Date: Wed, 19 Feb 2025 11:49:21 -0800
From: Jessica Zhang <quic_jesszhan@...cinc.com>
To: Rob Clark <robdclark@...il.com>,
        Dmitry Baryshkov
	<dmitry.baryshkov@...aro.org>,
        Sean Paul <sean@...rly.run>,
        Marijn Suijten
	<marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, "Simona
 Vetter" <simona@...ll.ch>
CC: Abhinav Kumar <quic_abhinavk@...cinc.com>, <linux-arm-msm@...r.kernel.org>,
        <dri-devel@...ts.freedesktop.org>, <freedreno@...ts.freedesktop.org>,
        <linux-kernel@...r.kernel.org>,
        "Jessica
 Zhang" <quic_jesszhan@...cinc.com>
Subject: [PATCH v3 5/5] drm/msm/dpu: rate limit snapshot capture for mmu
 faults

From: Abhinav Kumar <quic_abhinavk@...cinc.com>

There is no recovery mechanism in place yet to recover from mmu
faults for DPU. We can only prevent the faults by making sure there
is no misconfiguration.

Rate-limit the snapshot capture for mmu faults to once per
msm_atomic_commit_tail() as that should be sufficient to capture
the snapshot for debugging otherwise there will be a lot of DPU
snapshots getting captured for the same fault which is redundant
and also might affect capturing even one snapshot accurately.

Signed-off-by: Abhinav Kumar <quic_abhinavk@...cinc.com>
Signed-off-by: Jessica Zhang <quic_jesszhan@...cinc.com>
---
Changes in v3:
- Clear fault_snapshot_capture before calling prepare_commit() (Dmitry)
- Make fault_snapshot_capture an atomic variable (Dmitry, Abhinav)
---
 drivers/gpu/drm/msm/msm_atomic.c | 2 ++
 drivers/gpu/drm/msm/msm_kms.c    | 5 ++++-
 drivers/gpu/drm/msm/msm_kms.h    | 3 +++
 3 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/msm/msm_atomic.c b/drivers/gpu/drm/msm/msm_atomic.c
index 9c45d641b521..44b402e70925 100644
--- a/drivers/gpu/drm/msm/msm_atomic.c
+++ b/drivers/gpu/drm/msm/msm_atomic.c
@@ -221,6 +221,8 @@ void msm_atomic_commit_tail(struct drm_atomic_state *state)
 	kms->funcs->wait_flush(kms, crtc_mask);
 	trace_msm_atomic_wait_flush_finish(crtc_mask);
 
+	atomic_set(&kms->fault_snapshot_capture, 0);
+
 	/*
 	 * Now that there is no in-progress flush, prepare the
 	 * current update:
diff --git a/drivers/gpu/drm/msm/msm_kms.c b/drivers/gpu/drm/msm/msm_kms.c
index 1d3dae3d4c93..171462a8e08c 100644
--- a/drivers/gpu/drm/msm/msm_kms.c
+++ b/drivers/gpu/drm/msm/msm_kms.c
@@ -168,7 +168,10 @@ static int msm_kms_fault_handler(void *arg, unsigned long iova, int flags, void
 {
 	struct msm_kms *kms = arg;
 
-	msm_disp_snapshot_state(kms->dev);
+	if (atomic_read(&kms->fault_snapshot_capture) == 0) {
+		msm_disp_snapshot_state(kms->dev);
+		atomic_inc(&kms->fault_snapshot_capture);
+	}
 
 	return -ENOSYS;
 }
diff --git a/drivers/gpu/drm/msm/msm_kms.h b/drivers/gpu/drm/msm/msm_kms.h
index e60162744c66..3e28c4e012d2 100644
--- a/drivers/gpu/drm/msm/msm_kms.h
+++ b/drivers/gpu/drm/msm/msm_kms.h
@@ -128,6 +128,9 @@ struct msm_kms {
 	int irq;
 	bool irq_requested;
 
+	/* rate limit the snapshot capture to once per attach */
+	atomic_t fault_snapshot_capture;
+
 	/* mapper-id used to request GEM buffer mapped for scanout: */
 	struct msm_gem_address_space *aspace;
 

-- 
2.48.1