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From: Robin Murphy <robin.murphy@arm.com>
To: "Christoph Hellwig" <hch@lst.de>,
	"Pawel Osciak" <pawel@osciak.com>,
	"Marek Szyprowski" <m.szyprowski@samsung.com>,
	"Kyungmin Park" <kyungmin.park@samsung.com>,
	"Niklas Söderlund" <niklas.soderlund+renesas@ragnatech.se>
Cc: Russell King <linux@armlinux.org.uk>,
	linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	linuxppc-dev@lists.ozlabs.org,
	linux-arm-kernel@lists.infradead.org,
	linux-media@vger.kernel.org
Subject: Re: [PATCH 2/3] dma-mapping: don't BUG when calling dma_map_resource on RAM
Date: Mon, 14 Jan 2019 14:16:46 +0000	[thread overview]
Message-ID: <f8f9e4f0-87fc-9f4f-37ea-39297acc8d31@arm.com> (raw)
In-Reply-To: <20190111181731.11782-3-hch@lst.de>

On 11/01/2019 18:17, Christoph Hellwig wrote:
> Use WARN_ON_ONCE to print a stack trace and return a proper error
> code instead.

I was racking my brain to remember the reasoning behind BUG_ON() being 
the only viable way to prevent errors getting through unhandled, but of 
course that was before we had a standardised DMA_MAPPING_ERROR that 
would work across all implementations.

> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>   include/linux/dma-mapping.h | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
> index d3087829a6df..91add0751aa5 100644
> --- a/include/linux/dma-mapping.h
> +++ b/include/linux/dma-mapping.h
> @@ -353,7 +353,8 @@ static inline dma_addr_t dma_map_resource(struct device *dev,
>   	BUG_ON(!valid_dma_direction(dir));
>   
>   	/* Don't allow RAM to be mapped */

Ugh, I'm pretty sure that that "pfn_valid means RAM" misunderstanding 
originally came from me - it might be nice to have a less-misleading 
comment here, but off-hand I can't think of a succinct way to say "only 
for 'DMA' access to MMIO registers/SRAMs/etc. and not for anything the 
kernel knows as actual system/device memory" to better explain the WARN...

Either way, though,

Reviewed-by: Robin Murphy <robin.murphy@arm.com>

> -	BUG_ON(pfn_valid(PHYS_PFN(phys_addr)));
> +	if (WARN_ON_ONCE(pfn_valid(PHYS_PFN(phys_addr))))
> +		return DMA_MAPPING_ERROR;
>   
>   	if (dma_is_direct(ops))
>   		addr = dma_direct_map_resource(dev, phys_addr, size, dir, attrs);
> 

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  reply	other threads:[~2019-01-14 14:16 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CGME20190111181841epcas3p2d7c0bf8f5c11a9863e22ec1b12da6e1b@epcas3p2.samsung.com>
2019-01-11 18:17 ` fix a layering violation in videobuf2 and improve dma_map_resource Christoph Hellwig
2019-01-11 18:17   ` [PATCH 1/3] dma-mapping: remove the default map_resource implementation Christoph Hellwig
2019-01-14 13:12     ` Robin Murphy
2019-01-14 17:08       ` Christoph Hellwig
2019-01-11 18:17   ` [PATCH 2/3] dma-mapping: don't BUG when calling dma_map_resource on RAM Christoph Hellwig
2019-01-14 14:16     ` Robin Murphy [this message]
2019-01-11 18:17   ` [PATCH 3/3] videobuf2: replace a layering violation with dma_map_resource Christoph Hellwig
2019-01-11 19:54     ` Mauro Carvalho Chehab
2019-01-14 10:31       ` Christoph Hellwig
2019-01-14 11:04         ` Mauro Carvalho Chehab
2019-01-14 11:12           ` Christoph Hellwig
2019-01-14 12:42     ` Marek Szyprowski
2019-01-17 17:21       ` Christoph Hellwig
2019-01-18  9:41         ` Marek Szyprowski
2019-01-31 15:31           ` Christoph Hellwig
2019-01-14 11:43   ` fix a layering violation in videobuf2 and improve dma_map_resource Marek Szyprowski
2019-01-18 11:37 fix a layering violation in videobuf2 and improve dma_map_resource v2 Christoph Hellwig
2019-01-18 11:37 ` [PATCH 2/3] dma-mapping: don't BUG when calling dma_map_resource on RAM Christoph Hellwig

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