From: Christoph Hellwig <hch@lst.de>
To: Robin Murphy <robin.murphy@arm.com>
Cc: drinkcat@chromium.org, devicetree@vger.kernel.org,
heikki.krogerus@linux.intel.com, saravanak@google.com,
suzuki.poulose@arm.com, gregkh@linuxfoundation.org,
linux-kernel@vger.kernel.org, bgolaszewski@baylibre.com,
iommu@lists.linux-foundation.org, robh+dt@kernel.org,
Claire Chang <tientzu@chromium.org>,
dan.j.williams@intel.com, treding@nvidia.com,
frowand.list@gmail.com, hch@lst.de
Subject: Re: [PATCH 1/4] dma-mapping: Add bounced DMA ops
Date: Tue, 14 Jul 2020 13:01:41 +0200 [thread overview]
Message-ID: <20200714110141.GD16178@lst.de> (raw)
In-Reply-To: <4a2451f9-57d8-2e83-e1d6-f144f37173c0@arm.com>
On Mon, Jul 13, 2020 at 12:55:43PM +0100, Robin Murphy wrote:
> On 2020-07-13 10:12, Claire Chang wrote:
>> The bounced DMA ops provide an implementation of DMA ops that bounce
>> streaming DMA in and out of a specially allocated region. Only the
>> operations relevant to streaming DMA are supported.
>
> I think there are too many implicit assumptions here - apparently that
> coherent allocations will always be intercepted by
> dma_*_from_dev_coherent(), and that calling into dma-direct won't actually
> bounce things a second time beyond where you thought they were going,
> manage coherency for a different address, and make it all go subtly wrong.
> Consider "swiotlb=force", for instance...
>
> Again, plumbing this straight into dma-direct so that SWIOTLB can simply
> target a different buffer and always bounce regardless of masks would seem
> a far better option.
I haven't really had time to read through the details, but I agree that
any bouncing scheme should reuse the swiotlb code and not invent a
parallel infrastructure.
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next prev parent reply other threads:[~2020-07-14 11:01 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-13 9:12 [PATCH 0/4] Bounced DMA support Claire Chang
2020-07-13 9:12 ` [PATCH 1/4] dma-mapping: Add bounced DMA ops Claire Chang
2020-07-13 11:55 ` Robin Murphy
2020-07-14 11:01 ` Christoph Hellwig [this message]
2020-07-15 3:46 ` Claire Chang
2020-07-15 9:04 ` Claire Chang
2020-07-28 5:05 ` Claire Chang
2020-07-13 9:12 ` [PATCH 2/4] dma-mapping: Add bounced DMA pool Claire Chang
2020-07-13 9:12 ` [PATCH 3/4] dt-bindings: of: Add plumbing for " Claire Chang
2020-07-13 9:12 ` [PATCH 4/4] " Claire Chang
2020-07-13 11:39 ` [PATCH 0/4] Bounced DMA support Robin Murphy
2020-07-15 3:43 ` Claire Chang
2020-07-15 17:53 ` Robin Murphy
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