linux-kernel - Re: [PATCH v2] drm/panfrost: Don't try to map on error faults

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Message-ID: <9c0a0ac7-69fe-c799-c273-81e7a8cba2c7@arm.com>
Date:   Thu, 13 Feb 2020 11:13:29 +0000
From:   Steven Price <steven.price@....com>
To:     Rob Herring <robh@...nel.org>, linux-kernel@...r.kernel.org
Cc:     Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        David Airlie <airlied@...ux.ie>,
        dri-devel@...ts.freedesktop.org,
        Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH v2] drm/panfrost: Don't try to map on error faults

On 12/02/2020 20:22, Rob Herring wrote:
> From: Tomeu Vizoso <tomeu.vizoso@...labora.com>
> 
> If the exception type isn't a translation fault, don't try to map and
> instead go straight to a terminal fault.
> 
> Otherwise, we can get flooded by kernel warnings and further faults.
> 
> Signed-off-by: Tomeu Vizoso <tomeu.vizoso@...labora.com>
> Signed-off-by: Rob Herring <robh@...nel.org>
> ---
> I rewrote this some simplifying the code and somewhat following Steven's 
> suggested. Still not using defines though. No defines here was good 
> enough before IMO.

Heresy! It's a good thing you're not writing kbase code - there you
(seemingly) need to pick a #define which is as long as possible, but
then still wrap the code to avoid the 80 character limit... For
example[1]. Although shifting the code right might get you extra bonus
points, deep nesting seems to be encouraged! ;)

[1]
https://gitlab.freedesktop.org/panfrost/mali_kbase/blob/master/driver/product/kernel/drivers/gpu/arm/midgard/backend/gpu/mali_kbase_js_backend.c#L156

> 
> Only compile tested.

I've done some quick testing on a Firefly RK3288. But I don't have any
(handy) tests to trigger non-TRANSLATION_FAULT MMU faults.

Reviewed-by: Steven Price <steven.price@....com>

Thanks,

Steve

> 
>  drivers/gpu/drm/panfrost/panfrost_mmu.c | 44 +++++++++++--------------
>  1 file changed, 19 insertions(+), 25 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c b/drivers/gpu/drm/panfrost/panfrost_mmu.c
> index 763cfca886a7..4f2836bd9215 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_mmu.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c
> @@ -596,33 +596,27 @@ static irqreturn_t panfrost_mmu_irq_handler_thread(int irq, void *data)
>  		source_id = (fault_status >> 16);
>  
>  		/* Page fault only */
> -		if ((status & mask) == BIT(i)) {
> -			WARN_ON(exception_type < 0xC1 || exception_type > 0xC4);
> -
> +		ret = -1;
> +		if ((status & mask) == BIT(i) && (exception_type & 0xF8) == 0xC0)
>  			ret = panfrost_mmu_map_fault_addr(pfdev, i, addr);
> -			if (!ret) {
> -				mmu_write(pfdev, MMU_INT_CLEAR, BIT(i));
> -				status &= ~mask;
> -				continue;
> -			}
> -		}
>  
> -		/* terminal fault, print info about the fault */
> -		dev_err(pfdev->dev,
> -			"Unhandled Page fault in AS%d at VA 0x%016llX\n"
> -			"Reason: %s\n"
> -			"raw fault status: 0x%X\n"
> -			"decoded fault status: %s\n"
> -			"exception type 0x%X: %s\n"
> -			"access type 0x%X: %s\n"
> -			"source id 0x%X\n",
> -			i, addr,
> -			"TODO",
> -			fault_status,
> -			(fault_status & (1 << 10) ? "DECODER FAULT" : "SLAVE FAULT"),
> -			exception_type, panfrost_exception_name(pfdev, exception_type),
> -			access_type, access_type_name(pfdev, fault_status),
> -			source_id);
> +		if (ret)
> +			/* terminal fault, print info about the fault */
> +			dev_err(pfdev->dev,
> +				"Unhandled Page fault in AS%d at VA 0x%016llX\n"
> +				"Reason: %s\n"
> +				"raw fault status: 0x%X\n"
> +				"decoded fault status: %s\n"
> +				"exception type 0x%X: %s\n"
> +				"access type 0x%X: %s\n"
> +				"source id 0x%X\n",
> +				i, addr,
> +				"TODO",
> +				fault_status,
> +				(fault_status & (1 << 10) ? "DECODER FAULT" : "SLAVE FAULT"),
> +				exception_type, panfrost_exception_name(pfdev, exception_type),
> +				access_type, access_type_name(pfdev, fault_status),
> +				source_id);
>  
>  		mmu_write(pfdev, MMU_INT_CLEAR, mask);
>  
>