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From: Christoph Hellwig <hch@lst.de>
To: Robin Murphy <robin.murphy@arm.com>
Cc: "Christoph Hellwig" <hch@lst.de>,
	"Horia Geantă" <horia.geanta@nxp.com>,
	"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 15:09:21 +0200	[thread overview]
Message-ID: <20190522130921.GA26874@lst.de> (raw)
In-Reply-To: <6cbe5470-16a6-17e9-337d-6ba18b16b6e8@arm.com>

On Wed, May 22, 2019 at 01:50:47PM +0100, Robin Murphy wrote:
> 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.

Except that the same optimization we are tripping over here is also
present in dma_sync_* - dma_sync_*_to_device with DMA_FROM_DEVICE is a
no-op in swiotlb.

WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch@lst.de>
To: Robin Murphy <robin.murphy@arm.com>
Cc: "Horia Geantă" <horia.geanta@nxp.com>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@oracle.com>,
	linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org,
	linux-imx@nxp.com, "Christoph Hellwig" <hch@lst.de>
Subject: Re: [PATCH] swiotlb: sync buffer when mapping FROM_DEVICE
Date: Wed, 22 May 2019 15:09:21 +0200	[thread overview]
Message-ID: <20190522130921.GA26874@lst.de> (raw)
In-Reply-To: <6cbe5470-16a6-17e9-337d-6ba18b16b6e8@arm.com>

On Wed, May 22, 2019 at 01:50:47PM +0100, Robin Murphy wrote:
> 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.

Except that the same optimization we are tripping over here is also
present in dma_sync_* - dma_sync_*_to_device with DMA_FROM_DEVICE is a
no-op in swiotlb.
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  reply	other threads:[~2019-05-22 13:09 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
2019-05-22 12:50     ` Robin Murphy
2019-05-22 13:09     ` Christoph Hellwig [this message]
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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