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Message-ID: <39d5aabd-4c09-4135-a3d7-00f6da7a1684@arm.com>
Date:   Tue, 10 Oct 2023 10:40:44 +0100
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Subject: Re: [PATCH v2] dma-mapping: fix dma_addressing_limited if
 dma_range_map can't cover all system RAM
Content-Language: en-GB
To:     Christoph Hellwig <hch@lst.de>, Jia He <justin.he@arm.com>
Cc:     Marek Szyprowski <m.szyprowski@samsung.com>, iommu@lists.linux.dev,
        linux-kernel@vger.kernel.org
References: <20231010020835.3678-1-justin.he@arm.com>
 <20231010074816.GA9082@lst.de>
From:   Robin Murphy <robin.murphy@arm.com>
In-Reply-To: <20231010074816.GA9082@lst.de>
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On 2023-10-10 08:48, Christoph Hellwig wrote:
> dma_addressing_limited is called for every dma (direct) map, and this
> new code is way to heavy for that.  We'll need to cache the information
> somehow.

But is it? That was my instinctive reaction as well, but AFAICS it is 
only actually used by drivers in setup paths, either directly or via 
dma_max_mapping_size(). The dma_capable() check which we *do* use for 
every actual mapping still just checks whether the given physical 
address exists in the range map. I believe the underlying problem here 
is when dma_capable() say the mapping needs bouncing, but then it's too 
big for that to succeed, since dma_max_mapping_size() gave the wrong 
answer to start with.

Thanks,
Robin.