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

[Russell King - ARM Linux <linux@arm.linux.org.uk>]

On Sun, Dec 12, 2010 at 02:03:52PM +0000, Will Newton wrote:
> On Sun, Dec 12, 2010 at 1:52 PM, Chris Ball <cjb@laptop.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?

Maybe invent CONFIG_HAVE_MMIO_64BIT which architectures can select as
appropriate?