From: Christoph Hellwig <hch@lst.de>
To: Robin Murphy <robin.murphy@arm.com>
Cc: John Garry <john.garry@huawei.com>,
joro@8bytes.org, will@kernel.org, hch@lst.de,
m.szyprowski@samsung.com, chenxiang66@hisilicon.com,
thunder.leizhen@huawei.com, iommu@lists.linux-foundation.org,
linux-kernel@vger.kernel.org, liyihang6@hisilicon.com
Subject: Re: [RFC PATCH] dma-iommu: Add iommu_dma_max_mapping_size()
Date: Wed, 18 May 2022 15:13:53 +0200 [thread overview]
Message-ID: <20220518131353.GB26019@lst.de> (raw)
In-Reply-To: <8f193bdd-3a0a-f9ed-0726-e6081f374320@arm.com>
On Tue, May 17, 2022 at 01:02:00PM +0100, Robin Murphy wrote:
>> So how to inform the SCSI driver of this caching limit then so that it may
>> limit the SGL length?
>
> Driver-specific mechanism; block-layer-specific mechanism; redefine this
> whole API to something like dma_opt_mapping_size(), as a limit above which
> mappings might become less efficient or start to fail (callback to my
> thoughts on [1] as well, I suppose); many options. Just not imposing a
> ridiculously low *maximum* on everyone wherein mapping calls "should not be
> larger than the returned value" when that's clearly bollocks.
Well, for swiotlb it is a hard limit. So if we want to go down that
route we need two APIs, one for the optimal size and one for the
hard limit.
next prev parent reply other threads:[~2022-05-18 13:14 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-16 13:06 John Garry
2022-05-17 8:38 ` Christoph Hellwig
2022-05-17 9:02 ` John Garry
2022-05-17 9:11 ` Christoph Hellwig
2022-05-17 10:40 ` Robin Murphy
2022-05-17 11:26 ` John Garry
2022-05-17 12:02 ` Robin Murphy
2022-05-17 13:50 ` John Garry
2022-05-18 13:13 ` Christoph Hellwig [this message]
2022-05-20 8:51 ` Joerg Roedel
2022-05-18 13:12 ` Christoph Hellwig
2022-05-18 13:45 ` Robin Murphy
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