From: Christoph Hellwig <hch@infradead.org>
To: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Cc: ulf.hansson@linaro.org, wsa+renesas@sang-engineering.com,
linux-mmc@vger.kernel.org, linux-renesas-soc@vger.kernel.org,
iommu@lists.linux-foundation.org, linux-block@vger.kernel.org
Subject: Re: [PATCH v3 3/3] mmc: renesas_sdhi: use multiple segments if possible
Date: Wed, 22 May 2019 05:29:01 -0700 [thread overview]
Message-ID: <20190522122901.GA4583@infradead.org> (raw)
In-Reply-To: <1558520319-16452-4-git-send-email-yoshihiro.shimoda.uh@renesas.com>
On Wed, May 22, 2019 at 07:18:39PM +0900, Yoshihiro Shimoda wrote:
> In IOMMU environment, since it's possible to merge scatter gather
> buffers of memory requests to one iova, this patch changes the max_segs
> value when init_card of mmc_host timing to improve the transfer
> performance on renesas_sdhi_internal_dmac.
Well, you can't merge everything with an IOMMU. For one not every
IOMMU can merge multiple scatterlist segments, second even it can merge
segements the segments need to be aligned to the IOMMU page size. And
then of course we might have an upper limit on the total mapping.
> + if (host->pdata->max_segs < SDHI_MAX_SEGS_IN_IOMMU &&
> + host->pdev->dev.iommu_group &&
> + (mmc_card_mmc(card) || mmc_card_sd(card)))
> + host->mmc->max_segs = SDHI_MAX_SEGS_IN_IOMMU;
This is way to magic. We'll need a proper DMA layer API to expose
this information, and preferably a block layer helper to increase
max_segs instead of hacking that up in the driver.
next parent reply other threads:[~2019-05-22 12:29 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1558520319-16452-1-git-send-email-yoshihiro.shimoda.uh@renesas.com>
[not found] ` <1558520319-16452-4-git-send-email-yoshihiro.shimoda.uh@renesas.com>
2019-05-22 12:29 ` Christoph Hellwig [this message]
2019-05-23 4:15 ` [PATCH v3 3/3] mmc: renesas_sdhi: use multiple segments if possible Yoshihiro Shimoda
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