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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 15:34:00 +0200	[thread overview]
Message-ID: <20190522133400.GA27229@lst.de> (raw)
In-Reply-To: <fdfd7318-7999-1fe6-01b6-ae1fb7ba8c30@arm.com>

On Wed, May 22, 2019 at 02:25:38PM +0100, Robin Murphy wrote:
> Sure, but that should be irrelevant since the effective problem here is in 
> the sync_*_for_cpu direction, and it's the unmap which nobbles the buffer. 
> If the driver does this:
>
> 	dma_map_single(whole buffer);
> 	<device writes to part of buffer>
> 	dma_unmap_single(whole buffer);
> 	<contents of rest of buffer now undefined>
>
> then it could instead do this and be happy:
>
> 	dma_map_single(whole buffer, SKIP_CPU_SYNC);
> 	<device writes to part of buffer>
> 	dma_sync_single_for_cpu(updated part of buffer);
> 	dma_unmap_single(whole buffer, SKIP_CPU_SYNC);
> 	<contents of rest of buffer still valid>

Assuming the driver knows how much was actually DMAed this would
solve the issue.  Horia, does this work for you?
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WARNING: multiple messages have this Message-ID (diff)
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 15:34:00 +0200	[thread overview]
Message-ID: <20190522133400.GA27229@lst.de> (raw)
In-Reply-To: <fdfd7318-7999-1fe6-01b6-ae1fb7ba8c30@arm.com>

On Wed, May 22, 2019 at 02:25:38PM +0100, Robin Murphy wrote:
> Sure, but that should be irrelevant since the effective problem here is in 
> the sync_*_for_cpu direction, and it's the unmap which nobbles the buffer. 
> If the driver does this:
>
> 	dma_map_single(whole buffer);
> 	<device writes to part of buffer>
> 	dma_unmap_single(whole buffer);
> 	<contents of rest of buffer now undefined>
>
> then it could instead do this and be happy:
>
> 	dma_map_single(whole buffer, SKIP_CPU_SYNC);
> 	<device writes to part of buffer>
> 	dma_sync_single_for_cpu(updated part of buffer);
> 	dma_unmap_single(whole buffer, SKIP_CPU_SYNC);
> 	<contents of rest of buffer still valid>

Assuming the driver knows how much was actually DMAed this would
solve the issue.  Horia, does this work for you?

  reply	other threads:[~2019-05-22 13:34 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
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 [this message]
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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