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From: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
To: Christoph Hellwig <hch@lst.de>, Robin Murphy <robin.murphy@arm.com>
Cc: "ulf.hansson@linaro.org" <ulf.hansson@linaro.org>,
	"wsa+renesas@sang-engineering.com"
	<wsa+renesas@sang-engineering.com>,
	"m.szyprowski@samsung.com" <m.szyprowski@samsung.com>,
	"joro@8bytes.org" <joro@8bytes.org>,
	"linux-mmc@vger.kernel.org" <linux-mmc@vger.kernel.org>,
	"iommu@lists.linux-foundation.org"
	<iommu@lists.linux-foundation.org>,
	"linux-renesas-soc@vger.kernel.org" 
	<linux-renesas-soc@vger.kernel.org>
Subject: RE: [RFC PATCH v5 3/8] iommu: add a new capable IOMMU_CAP_MERGING
Date: Thu, 6 Jun 2019 06:28:47 +0000	[thread overview]
Message-ID: <OSAPR01MB3089448A3D44BE61B127AA73D8170@OSAPR01MB3089.jpnprd01.prod.outlook.com> (raw)
In-Reply-To: <20190605123808.GA12529@lst.de>

Hi Christoph,

Thank you for your comments!

> From: Christoph Hellwig, Sent: Wednesday, June 5, 2019 9:38 PM
> 
> On Wed, Jun 05, 2019 at 01:21:59PM +0100, Robin Murphy wrote:
> > And if the problem is really that you're not getting merging because of
> > exposing the wrong parameters to the DMA API and/or the block layer, or
> > that you just can't quite express your requirement to the block layer in
> > the first place, then that should really be tackled at the source rather
> > than worked around further down in the stack.
> 
> The problem is that we need a way to communicate to the block layer
> that more than a single segment is ok IFF the DMA API instance supports
> merging.  And of course the answer will depend on futher parameters
> like the maximum merged segment size and alignment for the segement.

I'm afraid but I don't understand why we need a way to communicate to
the block layer that more than a single segment is ok IFF the DMA API
instance supports merging.

> We'll need some way to communicate that, but I don't really think this
> is series is the way to go.

I should discard the patches 1/8 through 4/8.

> We'd really need something hanging off the device (or through a query
> API) how the dma map ops implementation exposes under what circumstances
> it can merge.  The driver can then communicate that to the block layer
> so that the block layer doesn't split requests up when reaching the
> segement limit.

The block layer already has a limit "max_segment_size" for each device so that
regardless it can/cannot merge the segments, we can use the limit.
Is my understanding incorrect?

Best regards,
Yoshihiro Shimoda


  reply	other threads:[~2019-06-06  6:28 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-05 11:11 [RFC PATCH v5 0/8] treewide: improve R-Car SDHI performance Yoshihiro Shimoda
2019-06-05 11:11 ` [RFC PATCH v5 1/8] dma-mapping: add a device driver helper for iova contiguous Yoshihiro Shimoda
2019-06-05 11:11 ` [RFC PATCH v5 2/8] iommu/dma: move iommu_dma_unmap_sg() place Yoshihiro Shimoda
2019-06-05 11:11 ` [RFC PATCH v5 3/8] iommu: add a new capable IOMMU_CAP_MERGING Yoshihiro Shimoda
2019-06-05 12:21   ` Robin Murphy
2019-06-05 12:38     ` Christoph Hellwig
2019-06-06  6:28       ` Yoshihiro Shimoda [this message]
2019-06-06  7:00         ` Christoph Hellwig
2019-06-07  5:41           ` Yoshihiro Shimoda
2019-06-07  5:49             ` Christoph Hellwig
2019-06-07  6:01               ` Yoshihiro Shimoda
2019-06-06  5:53     ` Yoshihiro Shimoda
2019-06-05 16:17   ` Sergei Shtylyov
2019-06-05 11:11 ` [RFC PATCH v5 4/8] iommu/ipmmu-vmsa: add capable ops Yoshihiro Shimoda
2019-06-05 11:11 ` [RFC PATCH v5 5/8] mmc: tmio: No memory size limitation if runs on IOMMU Yoshihiro Shimoda
2019-06-05 11:11 ` [RFC PATCH v5 6/8] mmc: tmio: Add a definition for default max_segs Yoshihiro Shimoda
2019-06-05 11:11 ` [RFC PATCH v5 7/8] mmc: renesas_sdhi: sort headers Yoshihiro Shimoda
2019-06-05 11:11 ` [RFC PATCH v5 8/8] mmc: renesas_sdhi: use multiple segments if possible Yoshihiro Shimoda

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