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

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Date:   Mon, 14 Jan 2019 17:57:55 +0100
From:   Christoph Hellwig <hch@....de>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Christoph Hellwig <hch@....de>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        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 Mon, Jan 14, 2019 at 04:52:40PM +0000, Robin Murphy wrote:
> 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?

None of this will with such segments.  But yes, I guess the old case
could have worked as long as any physical contigous ranges are also
virtually contigous.  So we might have to throw in a page size segment
boundary here.