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Date: Mon, 22 Jan 2024 08:34:23 +0100
From: Christoph Hellwig <hch@lst.de>
To: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
	Ming Lei <ming.lei@redhat.com>, linux-block@vger.kernel.org,
	linux-mmc@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
	Linus Walleij <linus.walleij@linaro.org>
Subject: mmc vs highmem, was: Re: [PATCH 2/2] blk-mq: ensure a
 q_usage_counter reference is held when splitting bios
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References: <20240112054449.GA6829@lst.de> <9eb0f18e-f3ce-497c-931d-339efee2190d@kernel.dk> <CAPDyKFpmEB9FGAmGAQNdEH+DtRtcCNnFszfv_ewihzUU9du+Xg@mail.gmail.com>
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On Mon, Jan 15, 2024 at 12:20:50PM +0100, Ulf Hansson wrote:
> Not sure exactly what problem you are trying to solve here, but I am
> certainly happy to help, if I can.
> 
> Can you perhaps point me to a couple of drivers that need to be converted?

Sure.

mmc_alloc_disk sets BLK_BOUNCE_HIGH for any mmc host that doesn't have a
DMA mask set, which is a bit odd as all proper devices should have a
valid DMA mask.  I suspect platform devices might sometimes not have
one, which historically was the wild west.

A better indicator might be the use of page_address in the I/O path,
which usually comes in the form of using the sg_virt() helper.
For drivers/mmc/ that seems to be: davinci_mmc, moxart-mmc, mvsdio,
mxcmmc, omap, sdhci-esdhc-mcf and sh_mmcif.

tmio_mmc_core on the other hand seems to have code properly kmapping
a scatterlist, which might be worth lifting into a common helper to
help the above drivers.

> 
> Kind regards
> Uffe
---end quoted text---