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From: Christoph Hellwig <hch@lst.de>
To: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Cc: Christoph Hellwig <hch@lst.de>,
	Robin Murphy <robin.murphy@arm.com>,
	"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: Fri, 7 Jun 2019 07:49:33 +0200	[thread overview]
Message-ID: <20190607054933.GA8267@lst.de> (raw)
In-Reply-To: <OSAPR01MB3089E3E79B0BDF24610FBEC2D8100@OSAPR01MB3089.jpnprd01.prod.outlook.com>

On Fri, Jun 07, 2019 at 05:41:56AM +0000, Yoshihiro Shimoda wrote:
> > bool blk_can_use_iommu_merging(struct request_queue *q, struct device *dev)
> > {
> > 	if (!IOMMU_CAN_MERGE_SEGMENTS(dev))
> > 		return false;
> 
> As Robin mentioned, all IOMMUs can merge segments so that we don't need
> this condition, IIUC. However, this should check whether the device is mapped
> on iommu by using device_iommu_mapped().

There are plenty of dma_map_ops based drivers that can't merge segments.
Examples:

 - arch/ia64/sn/pci/pci_dma.c
 - arch/mips/jazz/jazzdma.c
 - arch/sparc/mm/io-unit.c
 - arch/sparc/mm/iommu.c
 - arch/x86/kernel/pci-calgary_64.c

Nevermind the diret mapping, swiotlb and other weirdos.

> 
> > 	blk_queue_virt_boundary(q, IOMMU_PAGE_SIZE(dev));
> > 	blk_queue_max_segment_size(q, IOMMU_MAX_SEGMENT_SIZE(dev));
> 
> By the way, I reported an issue [1] and I'm thinking dima_is_direct() environment
> (especially for swiotlb) is also needed such max_segment_size changes somehow.
> What do you think?
> 
> [1]
> https://marc.info/?l=linux-block&m=155954415603356&w=2

That doesn't seem to be related to the segment merging.  I'll take
a look, but next time please Cc the author of a suspect commit if
you already bisect things.

  reply	other threads:[~2019-06-07  5:50 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
2019-06-06  7:00         ` Christoph Hellwig
2019-06-07  5:41           ` Yoshihiro Shimoda
2019-06-07  5:49             ` Christoph Hellwig [this message]
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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