Re: [PATCH v6 2/2] clocksource: add J-Core timer/clocksource driver

Arnd Bergmann
2016-08-25T10:24:13Z

On Wednesday, August 24, 2016 11:57:08 PM CEST Arnd Bergmann wrote:
> > I'm not familiar with those classifications, but from what I can tell,
> > BE32 describes it correctly. I'll see if I can get someone to verify
> > this. Is there a reason it's not widely used anymore? Perhaps
> > something related to supporting misaligned word-sized loads/stores?
>
> The main problem I see is that you can't easily use MMIO registers that
> are not 32-bit wide -- you end up having to flip not just the register
> contents but also the lower bits of the address in order to reach
> the right contents of the register.
>

Actually there is a much more serious problem with BE32/LE32 mode:
doing unaligned access to RAM is a huge pain at the HW level,
and also when emulating it in the kernel on CPUs that require
aligned access. In ARM THUMB2 mode, you can even have unaligned
32-bit instructions.

Arnd