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From: Horia Geanta <horia.geanta@nxp.com>
To: Christoph Hellwig <hch@lst.de>,
	Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Robin Murphy <robin.murphy@arm.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	"iommu@lists.linux-foundation.org"
	<iommu@lists.linux-foundation.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	dl-linux-imx <linux-imx@nxp.com>
Subject: Re: [PATCH] swiotlb: sync buffer when mapping FROM_DEVICE
Date: Thu, 23 May 2019 17:53:51 +0000	[thread overview]
Message-ID: <AM0PR0402MB3476A633E03202C26D15CB5698010@AM0PR0402MB3476.eurprd04.prod.outlook.com> (raw)
In-Reply-To: <20190523164332.GA22245@lst.de>

On 5/23/2019 7:43 PM, Christoph Hellwig wrote:
> On Thu, May 23, 2019 at 07:35:07AM +0200, Marek Szyprowski wrote:
>> Don't we have DMA_BIDIRECTIONAL for such case?
> 
> Not sure if it was intended for that case, but it definitively should
> do the right thing for swiotlb, and it should also do the right thing
> in terms of cache maintainance.
> 
>> Maybe we should update 
>> documentation a bit to point that DMA_FROM_DEVICE expects the whole 
>> buffer to be filled by the device?
> 
> Probably. Horia, can you try to use DMA_BIDIRECTIONAL?
> 
This works, but at the cost of performance - all the cache lines being written
back to memory, just to be overwritten by the device.

Thanks,
Horia

  reply	other threads:[~2019-05-23 17:53 UTC|newest]

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

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