[PATCH] map-ram chip driver: 16-bit block transfer

[Arnd Bergmann]

On Fri, Aug 11, 2017 at 11:03 PM, Sanjay Tandel
<sanjay.tandel at rockwellcollins.com> wrote:
> On Fri, Aug 11, 2017 at 2:41 PM, Arnd Bergmann <arnd at arndb.de> wrote:
>> On Fri, Aug 11, 2017 at 6:50 PM, Sanjay Tandel
>> On almost all ARM platforms, it would use 32-bit accesses these days. On what
>> kernel version, ARM platform and endianess do you see memcpy_toio() use 8-bit
>> access?
>>
>
> We use version 4.1.8 with Freescale LS1021A( cortex-a7 core, little-endian).
> With the newer versions of kernel also, I can see same 8-bit
> implementation for 32-bit ARM arch.

I see. Commit 7ddfe625cbc1 ("ARM: optimize
memset_io()/memcpy_fromio()/memcpy_toio()")
was merged in linux-4.2 and changed this to use mostly 32-bit accesses and a
bug in it fixed in commit 1bd46782d08b ("ARM: avoid unwanted GCC
memset()/memcpy() optimisations for IO variants").


> BTW, for other arch also memcpy_toio()  uses combination of  32-bit(or
> 64-bit) and 8-bit accesses,
> which may not work here.Because we need all accesses to be of same
> size(bank-width).

Could you try with a newer kernel or with the 7ddfe625cbc1/1bd46782d08b
commits backported to see if that works for you though? At the very least that
should impact the description of the patch we end up applying, since your
current text no longer matches what the kernel does.

      Arnd