From: Christoph Hellwig <hch@lst.de>
To: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: axboe@kernel.dk, linux-renesas-soc@vger.kernel.org,
ulf.hansson@linaro.org, linux-mmc@vger.kernel.org, hch@lst.de,
linux-block@vger.kernel.org, wsa+renesas@sang-engineering.com,
iommu@lists.linux-foundation.org, robin.murphy@arm.com
Subject: Re: [RFC PATCH v7 2/5] iommu/dma: Add a new dma_map_ops of get_merge_boundary()
Date: Mon, 24 Jun 2019 08:21:57 +0200 [thread overview]
Message-ID: <20190624062157.GB2989@lst.de> (raw)
In-Reply-To: <8bce95ea-93ac-e783-af7c-ec5bfb8e82f6@samsung.com>
On Fri, Jun 21, 2019 at 09:59:21AM +0200, Marek Szyprowski wrote:
> Hi,
>
> On 2019-06-20 10:50, Yoshihiro Shimoda wrote:
> > This patch adds a new dma_map_ops of get_merge_boundary() to
> > expose the DMA merge boundary if the domain type is IOMMU_DOMAIN_DMA.
> >
> > Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
> > ---
> > drivers/iommu/dma-iommu.c | 11 +++++++++++
> > 1 file changed, 11 insertions(+)
> >
> > diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> > index 205d694..9950cb5 100644
> > --- a/drivers/iommu/dma-iommu.c
> > +++ b/drivers/iommu/dma-iommu.c
> > @@ -1091,6 +1091,16 @@ static int iommu_dma_get_sgtable(struct device *dev, struct sg_table *sgt,
> > return ret;
> > }
> >
> > +static unsigned long iommu_dma_get_merge_boundary(struct device *dev)
> > +{
> > + struct iommu_domain *domain = iommu_get_dma_domain(dev);
> > +
> > + if (domain->type != IOMMU_DOMAIN_DMA)
> > + return 0; /* can't merge */
> > +
> > + return (1 << __ffs(domain->pgsize_bitmap)) - 1;
> > +}
>
> I really wonder if there is any IOMMU, which doesn't support 4KiB pages.
> Cannot you simply assume that the merge boundary is 4KiB and avoid
> adding this new API?
No idea if we have one, but I would not be surprised if one shows
up on a system only built to run with 64k pages for example.
Either way the abstraction seems light and self-explanatory, so I see
now reason not to have it even if we assume it would always return
4k, especially as we'd also still need a flag at the dma_map_ops level
to indicate if segement merging is supported at all.
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next prev parent reply other threads:[~2019-06-24 6:22 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-20 8:50 [RFC PATCH v7 0/5] treewide: improve R-Car SDHI performance Yoshihiro Shimoda
2019-06-20 8:50 ` [RFC PATCH v7 1/5] dma: Introduce dma_get_merge_boundary() Yoshihiro Shimoda
2019-06-24 6:20 ` Christoph Hellwig
2019-06-20 8:50 ` [RFC PATCH v7 2/5] iommu/dma: Add a new dma_map_ops of get_merge_boundary() Yoshihiro Shimoda
2019-06-21 7:59 ` Marek Szyprowski
2019-06-24 6:21 ` Christoph Hellwig [this message]
2019-06-20 8:50 ` [RFC PATCH v7 3/5] block: sort headers on blk-setting.c Yoshihiro Shimoda
2019-06-20 8:50 ` [RFC PATCH v7 4/5] block: add a helper function to merge the segments Yoshihiro Shimoda
2019-06-24 6:22 ` Christoph Hellwig
2019-06-20 8:50 ` [RFC PATCH v7 5/5] mmc: queue: Use bigger segments if DMA MAP layer can " Yoshihiro Shimoda
2019-06-24 6:24 ` Christoph Hellwig
2019-07-08 11:45 ` Ulf Hansson
2019-07-01 8:32 ` [RFC PATCH v7 0/5] treewide: improve R-Car SDHI performance Christoph Hellwig
2019-07-08 11:45 ` Ulf Hansson
2019-07-08 16:22 ` Christoph Hellwig
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