IOMMU Archive on lore.kernel.org
 help / color / Atom feed
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
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.
_______________________________________________
iommu mailing list
iommu@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/iommu

  reply index

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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200714110141.GD16178@lst.de \
    --to=hch@lst.de \
    --cc=bgolaszewski@baylibre.com \
    --cc=dan.j.williams@intel.com \
    --cc=devicetree@vger.kernel.org \
    --cc=drinkcat@chromium.org \
    --cc=frowand.list@gmail.com \
    --cc=gregkh@linuxfoundation.org \
    --cc=heikki.krogerus@linux.intel.com \
    --cc=iommu@lists.linux-foundation.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=robh+dt@kernel.org \
    --cc=robin.murphy@arm.com \
    --cc=saravanak@google.com \
    --cc=suzuki.poulose@arm.com \
    --cc=tientzu@chromium.org \
    --cc=treding@nvidia.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

IOMMU Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-iommu/0 linux-iommu/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-iommu linux-iommu/ https://lore.kernel.org/linux-iommu \
		iommu@lists.linux-foundation.org
	public-inbox-index linux-iommu

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.linux-foundation.lists.iommu


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git