Re: [PATCH v2 10/19] MIPS: asm: mips-cm: Extend CM accessors for 64-bit CPUs

[Markos Chandras <Markos.Chandras@imgtec.com>]

On 07/14/2015 09:35 AM, Paul Burton wrote:
> On Tue, Jul 14, 2015 at 09:30:19AM +0100, Paul Burton wrote:
>> On Tue, Jul 14, 2015 at 09:14:12AM +0100, Markos Chandras wrote:
>>> Previously, the CM accessors were only accessing CM registers as u32
>>> types instead of using the native CM register with. However, newer CMs
>>> may actually be 64-bit on MIPS64 cores. Fortunately, current 64-bit CMs
>>> (CM3) hold all the useful configuration bits in the lower half of the
>>> 64-bit registers (at least most of them) so they can still be accessed
>>> using the current 32-bit accessors.
>>>
>>> Cc: Thomas Gleixner <tglx@linutronix.de>
>>> Cc: Jason Cooper <jason@lakedaemon.net>
>>> Cc: Andrew Bresticker <abrestic@chromium.org>
>>> Cc: Paul Burton <paul.burton@imgtec.com>
>>> Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
>>> ---
>>> Changes since v1
>>> - Use 32-bit CM I/O on 32-bit kernels
>>
>> A concern I have, but haven't yet drank enough coffee to think through
>> fully, is whether this will work on big endian systems. These are 64b
>> addresses and you're writing 32b to their addresses which I suspect may
>> go horribly wrong.
> 
> Should be:
> 
> "These are 64b registers and you're writing 32b to their addresses"
> 
> Apparently I haven't drunk enouugh coffee to formulate sentences yet
> either ;)
> 
> Thanks,
>     Paul
> 

The HW team told me that the CM regs can be accessed in LE-pair format
even on big-endian cores in the sense that bit0 of a 64-bit CM reg will
always be on the lower address. I have never tested that really.

-- 
markos