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From: Robin Murphy <robin.murphy@arm.com>
To: "Christoph Hellwig" <hch@lst.de>, "Horia Geantă" <horia.geanta@nxp.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
	linux-imx@nxp.com
Subject: Re: [PATCH] swiotlb: sync buffer when mapping FROM_DEVICE
Date: Wed, 22 May 2019 13:50:47 +0100	[thread overview]
Message-ID: <6cbe5470-16a6-17e9-337d-6ba18b16b6e8@arm.com> (raw)
In-Reply-To: <20190522123243.GA26390@lst.de>

On 22/05/2019 13:32, Christoph Hellwig wrote:
> I'm a little worried about this.  While it looks functionally correct
> we have surived without it, and doing another copy for every swiotlb
> dma mapping from the device looks extremely painful for the typical use
> cases where we expect the device to transfer the whole mapping.
> 
> I'd be tempted to instead properl document the current behavior and
> introduce a new DMA_ATTR_PARTIAL flag to allow for partial mappings.

Would that work out any different from the existing 
DMA_ATTR_SKIP_CPU_SYNC? If drivers are prepared to handle this issue 
from their end, they can already do so for single mappings by using that 
attr along with explicit partial syncs via dma_sync_single(). For 
page/sg mappings we'd still have the problem of identifying what part of 
"partial" actually matters, and probably having to add some additional 
new sync operations to cope.

Robin.

WARNING: multiple messages have this Message-ID (diff)
From: Robin Murphy <robin.murphy@arm.com>
To: "Christoph Hellwig" <hch@lst.de>, "Horia Geantă" <horia.geanta@nxp.com>
Cc: linux-imx@nxp.com, iommu@lists.linux-foundation.org,
	linux-kernel@vger.kernel.org,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Subject: Re: [PATCH] swiotlb: sync buffer when mapping FROM_DEVICE
Date: Wed, 22 May 2019 13:50:47 +0100	[thread overview]
Message-ID: <6cbe5470-16a6-17e9-337d-6ba18b16b6e8@arm.com> (raw)
In-Reply-To: <20190522123243.GA26390@lst.de>

On 22/05/2019 13:32, Christoph Hellwig wrote:
> I'm a little worried about this.  While it looks functionally correct
> we have surived without it, and doing another copy for every swiotlb
> dma mapping from the device looks extremely painful for the typical use
> cases where we expect the device to transfer the whole mapping.
> 
> I'd be tempted to instead properl document the current behavior and
> introduce a new DMA_ATTR_PARTIAL flag to allow for partial mappings.

Would that work out any different from the existing 
DMA_ATTR_SKIP_CPU_SYNC? If drivers are prepared to handle this issue 
from their end, they can already do so for single mappings by using that 
attr along with explicit partial syncs via dma_sync_single(). For 
page/sg mappings we'd still have the problem of identifying what part of 
"partial" actually matters, and probably having to add some additional 
new sync operations to cope.

Robin.
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iommu@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/iommu

  reply	other threads:[~2019-05-22 12:50 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-22  7:20 [PATCH] swiotlb: sync buffer when mapping FROM_DEVICE Horia Geantă
2019-05-22  7:20 ` Horia Geantă
2019-05-22 12:32 ` Christoph Hellwig
2019-05-22 12:32   ` Christoph Hellwig
2019-05-22 12:50   ` Robin Murphy [this message]
2019-05-22 12:50     ` Robin Murphy
2019-05-22 13:09     ` Christoph Hellwig
2019-05-22 13:09       ` Christoph Hellwig
2019-05-22 13:25       ` Robin Murphy
2019-05-22 13:25         ` Robin Murphy
2019-05-22 13:34         ` Christoph Hellwig
2019-05-22 13:34           ` Christoph Hellwig
2019-05-22 13:55           ` Robin Murphy
2019-05-22 13:55             ` Robin Murphy
2019-05-23  5:35             ` Marek Szyprowski
2019-05-23  5:35               ` Marek Szyprowski
2019-05-23 16:25               ` Horia Geanta
2019-05-23 16:25                 ` Horia Geanta
2019-05-23 16:43               ` Christoph Hellwig
2019-05-23 16:43                 ` Christoph Hellwig
2019-05-23 17:53                 ` Horia Geanta
2019-05-23 17:53                   ` Horia Geanta
2019-05-23 18:05                 ` Robin Murphy
2019-05-23 18:05                   ` Robin Murphy

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