drm/msm/dpu: rate limit snapshot capture for mmu faults

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@quicinc.com>
Signed-off-by: Jessica Zhang <quic_jesszhan@quicinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/638362/
Link: https://lore.kernel.org/r/20250219-abhinavk-smmu-fault-handler-v3-5-aa3f0bf4434a@quicinc.com


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

drivers/gpu/drm/msm/msm_atomic.c

@@ -232,6 +232,8 @@ 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:

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;
 }

drivers/gpu/drm/msm/msm_kms.h

@@ -135,6 +135,9 @@ 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;