[PATCH v2] mtd mxc_nand: use 32bit copy functions

[Sascha Hauer]

On Tue, May 29, 2012 at 10:39:48AM +0100, Russell King - ARM Linux wrote:
> On Tue, May 29, 2012 at 11:36:29AM +0200, Sascha Hauer wrote:
> > On Tue, May 29, 2012 at 11:12:54AM +0200, Uwe Kleine-König wrote:
> > > Hello,
> > > 
> > > On Tue, May 29, 2012 at 10:16:09AM +0200, Sascha Hauer wrote:
> > > > The following commit changes the function used to copy from/to
> > > > the hardware buffer to memcpy_[from|to]io. This does not work
> > > > since the hardware cannot handle the byte accesses used by these
> > > > functions. Instead of reverting this patch introduce 32bit
> > > > correspondents of these functions.
> > > Hmm, I didn't run an mtd test suite, but on mx27 it worked for me. IMHO
> > > it's surprising that memcpy used to work, but memcpy_fromio doesn't. I
> > > wouldn't expect a different semantic (apart from normal vs. __iomem
> > > memory). And I wonder what will break when ARM's memcpy_fromio et al.
> > > is optimized.
> > 
> > Have a look at the (ARM) implementation of memcpy_fromio:
> > 
> > void _memcpy_fromio(void *to, const volatile void __iomem *from, size_t count)
> > {
> > 	unsigned char *t = to;
> > 	while (count) {
> > 		count--;
> > 		*t = readb(from);
> > 		t++;
> > 		from++;
> > 	}
> > }
> > 
> > Appearently this uses byte accesses which do not work on NFC SRAM,
> > whereas memcpy uses optimized (so 32bit whenever possible) accesses.
> > If someone would implement an optimized version of memcpy_fromio, it
> > would work for the NFC aswell.
> > 
> > btw on i.MX27 byte accesses also do not work on NFC SRAM, so I doubt
> > this worked for you.
> 
> And then when you ask for an odd alignment or an odd number of bytes...

Then the person will get an oops and hopefully report it, which so far
did not happen. I could try and implement this, but I rather don't do
this as long as we don't know what it's used for and thus we can check
that the result is correct.

Sascha

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