[PATCH] ARM: shmobile: Check r8a7791 MD21 at SMP boot

[Geert Uytterhoeven]

Hi Magnus,

On Thu, Feb 27, 2014 at 4:33 AM, Magnus Damm <magnus.damm at gmail.com> wrote:
>>>  This is a reworked version of the APMU patch previously posted as
>>>  [PATCH] ARM: shmobile: Check MD21 at SMP boot in case of APMU
>>
>> Your previous version also affected r8a7790/Lager.
>> Isn't this check no longer needed there? According to the Lager manual,
>> MD21 also enables hardware debug mode, and is also controlled by
>> SW8-4. Of course the CPU may behave differently, as the CPU cores
>> are different.
>
> Yes, you are correct that the previous version of the patch also
> affected Lager. And that both r8a7790 and r8a7791 mention the MD21 bit
> together with JTAG debugging.
>
> I recently used the patch on Lager and I discovered that I apparently
> had been running with MD21 on my Lager since forever, and surprisingly
> it worked regardless. Since there is no documentation on r8a7790 or
> r8a7791 I simply decided to handle them separately and only enable
> where it is needed.

You could have been lucky?

On Koelsch, I only had failures after Real Cold Boot, i.e. on boot up in the
morning. And not always, so there could be a timing issue involved.

> I've also been told that it is possible to allow SMP operation
> together with JTAG, apparently some magic with RST is needed. It seems
> that the power domains are treated differently depending on the MD21
> setting. Not sure if this applies to both r8a7790 and r8a7791, but if
> we end up with similar fixes we can consolidate. Until then I think
> dealing with them one by one makes sense.

Furthermore, I haven't seen any SPI timeouts after I disabled MD21 (holding
wood, and rabbit legs ;-). So the SMP memory (in)coherency I saw there
could have been caused by a wobbly SMP setup.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds