[PATCH] drm/etnaviv: print MMU exception cause

[Philipp Zabel]

On Mi, 2022-11-30 at 19:53 +0100, Lucas Stach wrote:
From: Christian Gmeiner <christian.gmeiner at gmail.com>

The MMU tells us the fault status. While the raw register value is
already printed, it's a bit more user friendly to translate the
fault reasons into human readable format.

Signed-off-by: Christian Gmeiner <christian.gmeiner at gmail.com>
Signed-off-by: Lucas Stach <l.stach at pengutronix.de>
---
I've rewritten parts of the patch to properly cover multiple
MMUs and squashed the reason into the existing message. Christian,
please tell me if you are fine with having your name attached to
this patch.
---
 drivers/gpu/drm/etnaviv/etnaviv_gpu.c | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gpu.c b/drivers/gpu/drm/etnaviv/etnaviv_gpu.c
index 37018bc55810..f79203b774d9 100644
--- a/drivers/gpu/drm/etnaviv/etnaviv_gpu.c
+++ b/drivers/gpu/drm/etnaviv/etnaviv_gpu.c
@@ -1426,6 +1426,15 @@ static void sync_point_worker(struct work_struct *work)
 

 static void dump_mmu_fault(struct etnaviv_gpu *gpu)
 {
+	static const char *fault_reasons[] = {
+		"slave not present",
+		"page not present",
+		"write violation",
+		"out of bounds",
+		"read security violation",
+		"write security violation",
+	};
+
 	u32 status_reg, status;
 	int i;
 

@@ -1438,18 +1447,25 @@ static void dump_mmu_fault(struct etnaviv_gpu *gpu)
 	dev_err_ratelimited(gpu->dev, "MMU fault status 0x%08x\n", status);
 

 	for (i = 0; i < 4; i++) {
+		const char *reason = "unknown";
 		u32 address_reg;
+		u32 mmu_status;
 

-		if (!(status & (VIVS_MMUv2_STATUS_EXCEPTION0__MASK << (i * 4))))
+		mmu_status = (status >> (i * 4)) & VIVS_MMUv2_STATUS_EXCEPTION0__MASK;

VIVS_MMUv2_STATUS_EXCEPTION0__MASK is 0x3 ...

+		if (!mmu_status)
 			continue;
 

+		if ((mmu_status - 1) < ARRAY_SIZE(fault_reasons))
+			reason = fault_reasons[mmu_status - 1];

... so (mmu_status - 1) can be 2 at most. This leaves me wondering how
"out of bounds" and the "security violation" errors can be reached. I
think this requires the exception bitfield masks to be extended to 0x7.

regards
Philipp