linux-kernel - Re: remove block layer bounce buffering for MMC

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Date:   Mon, 14 Jan 2019 16:52:40 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Christoph Hellwig <hch@....de>,
        Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Aaro Koskinen <aaro.koskinen@....fi>,
        Nicolas Pitre <nico@...xnic.net>, linux-mmc@...r.kernel.org,
        Russell King <linux@...linux.org.uk>,
        linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        Ben Dooks <ben-linux@...ff.org>, linux-omap@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: remove block layer bounce buffering for MMC

On 14/01/2019 09:57, Christoph Hellwig wrote:
> Hi everyone,
> 
> this series converts the remaining MMC host drivers to properly kmap the
> scatterlist entries it does PIO operations on, and then goes on to
> remove the usage of block layer bounce buffering (which I plan to remove
> eventually) from the MMC layer.
> 
> As a bonus I've converted various drivers to the proper scatterlist
> helpers so that at least in theory they are ready for chained
> scatterlists.
> 
> All the changes are compile tested only as I don't have any of the
> hardware, so a careful review would be appreciated.

One general point for the kmap() conversions - it's not obvious (to me 
at least) whether or how that would work for a segment where sg->length 
 > PAGE_SIZE. Or is there some cast-iron guarantee from the MMC 
mid-layer that it will never let the block layer generate such things in 
the first place?

Robin.