linux-kernel - Re: [PATCH] dw_mmc: Add Synopsys DesignWare mmc host driver.

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Date:	Sun, 12 Dec 2010 14:03:52 +0000
From:	Will Newton <will.newton@...il.com>
To:	Chris Ball <cjb@...top.org>
Cc:	Linux Kernel list <linux-kernel@...r.kernel.org>,
	linux-mmc@...r.kernel.org, Matt Fleming <matt@...sole-pimps.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] dw_mmc: Add Synopsys DesignWare mmc host driver.

On Sun, Dec 12, 2010 at 1:52 PM, Chris Ball <cjb@...top.org> wrote:
> Hi Will,
>
> On Sun, Dec 12, 2010 at 10:57:44AM +0000, Will Newton wrote:
>> > drivers/mmc/host/dw_mmc.c: In function ‘dw_mci_pull_data64’:
>> > drivers/mmc/host/dw_mmc.c:998: error: implicit declaration of function ‘__raw_readq’
>> >
>> > because arch/arm doesn't implement raw versions of these 64-bit accesses.
>> > I'm surprised that this driver hasn't been compiled on ARM before!  What
>>
>> That particular bit of code has been added since it was last built for
>> arm. Our architecture can do 64bit accesses so we implement readq.
>> Unfortunately there doesn't seem to be a sane way to conditionalize
>> code for architectures that have or don't have readq, so I suspect
>> I'll have to just remove that branch of the if statement for now.
>
> (Russell, thanks for the excellent explanation.)
>
> Other drivers (MTD, gpio/basic_mmio_gpio.c, fs/fuse, pcm_oss.c)
> conditionalize uses of {read,write}q on BITS_PER_LONG >= 64, so
> something like this:

I don't think that's going to work, BITS_PER_LONG isn't equivalent to
"can do 64bit IO accesses", at least it isn't on our architecture. x86
is in the same situation it would appear, although x86 does explicitly
#define readq so it may be possible to #ifdef on that?
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