[PATCH 3/3] ARM: Map the lowmem and kernel separately

[Grygorii Strashko]

On 31/07/2021 01:40, Linus Walleij wrote:
> On Fri, Jul 30, 2021 at 10:23 PM Nishanth Menon <nm at ti.com> wrote:
>> On 16:57-20210517, Linus Walleij wrote:
>>> Using our knowledge of where the physical kernel sections start
>>> and end we can split mapping of lowmem and kernel apart.
>>>
>> [...]
>>>
>>> Signed-off-by: Linus Walleij <linus.walleij at linaro.org>
>>
>>
>> We noticed a regression in k2g platforms with this patch.
>> commit 6e121df14ccd ("ARM: 9090/1: Map the lowmem and kernel
>> separately")
>>
>> Boot log: https://pastebin.ubuntu.com/p/Sf3r28D8MR/
>> Bisect log: https://pastebin.ubuntu.com/p/6PTYpNVFDy/
> 
> Given how invasive the patch is I'm surprised that k2g is the
> only thing so far complaining about it. Let's fix this!
> 
> I've had similar reports and in those cases it has been that the boot
> loader did not turn off the caches before jumping to execute the
> Linux kernel.
> 
> So first can you check that cache is off?
> 
> Next can you turn on DEBUG_LL and enable the debug messages
> in arch/arm/mmu.c in map_lowmem() in some way that works for
> you, for example I just add a patch like this:
> https://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-integrator.git/patch/?id=d10c46631a6eaef1339e376b878de985143b27ff
> (Beware of ugly debug habits!)
> 
> Next is this using the keystone 2 pv fixup thing  mdesc->pv_fixup
> mdesc->pv_fixup in early_paging_init()?
> 
> I added a special print
> there to see if that gets called. This code is really scary but I
> suppose Santosh can explain what is supposed to happen here
> and what I may have stepped on. (I see Santosh work at Oracle
> now? Interesting.)

It should be called on all keystone 2 platforms by default (LAPE is default mode for K2).

Huh. Below as I remember it:
- K2 starts using memory window (aliased memory) at 00 8000 0000 (No IO coherency is supported)
- K2, early at boot, is switching to LPAE memory window 08 0000 0000 (IO coherency is supported)
   so all, already mapped memory, has to be fixed - phys addresses.


-- 
Best regards,
grygorii