[PATCH] drm/etnaviv: print MMU exception cause

[Lucas Stach]

Hi Philipp,

Am Donnerstag, dem 01.12.2022 um 09:40 +0100 schrieb 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];
> 
Your mail quoting seems to be broken, again.

> ... 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.

Good catch! That's a inconsistency in rnndb, where we claim to be able
to stuff the full exception enum into 2 bits. Will fix!

Regards,
Lucas