On 2014-12-18 23:44, Arnd Bergmann wrote:

On Thursday 18 December 2014 21:36:31 Stefan Agner wrote:

quoted

On 2014-12-17 13:31, Arnd Bergmann wrote:

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On Wednesday 17 December 2014 00:41:33 Stefan Agner wrote:

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On 2014-12-03 12:03, Arnd Bergmann wrote:

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Starting with v3.19, you should be able to use the earlycon framework on
arm32, so it would be better to replace earlyprintk with earlycon here
and add a stdout-path property in chosen that points to the console
uart.

I started to implement earlycon support, but something currently fails
when earlycon tries to map the UART registers:
[    0.000000] earlycon_map: Couldn't map 0x40027000

I traced the issue a bit further down and found that get_vm_area_caller
returns NULL (in __arm_ioremap_pfn_caller). This happend on Linus master
as of today (2dbfca5a181973558277b28b1f4c36362291f5e0). Do I miss
something here?

Hmm, I fear the arm32 FIX_EARLYCON_MEM support ended up not making it
into 3.19 after all.

Is it because early_ioremap and fixmap still missing for arm32?
According to Rob's patchset from spring fixmap is required, there is
something in this tree:
https://git.kernel.org/cgit/linux/kernel/git/robh/linux.git/log/?h=arm-fixmap

Right, that's the one, thanks for finding that again. There are five
patches on that branch. The first three got merged, and the one we
need is just the last one (ARM: fixmap early permanent mapping support),
but the implementation depends on the previous patch (arm: add
early_ioremap support).

I was hoping we'd see both of them in 3.19, but apparently Rob didn't
submit the latest version. If you don't mind, could you try forward-porting
them to the latest kernel and then submit them for inclusion? You could
also try adapting the last patch to work without the early_ioremap
support that we don't really need that urgently on arm32.

Looked into that a bit more in depth. I tried creating a patch which
adds just what is necessary to support FIX_EARLYCON_MEM. Fixmap seems to
be in place, just for earlycon it would need a fixmap entry with
FIX_EARLYCON_MEM_BASE. And I guess later during boot, it would need a
call to create_mapping to create a permanent mapping of it.

Currently I'm stuck in the __set_fixmap call, on set_pte_ext call the
kernel freezes. The arguments look fine as far as I can tell (vaddr
ffeff000, phys 40027000, pgprot is FIXMAP_PAGE_IO, defined as in Rob's
patchset). 

Afaik, initialization for early fixmap is missing, I guess we could do
something which looks similar to what ARM64 has now:

https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/commit/?id=af86e5974d3069bd26ebcf7c046c6e59726acaaa

I'm wondering what the value is of __set_fixmap without that, as is
right now? I still need to understand the whole MM stuff a bit more. I
will be away the next couple of days, but will have a look into it
towards the end of the year. But if anyone else can help make that
happen (who might be better in the picture of fixmap than I am), I'm
happy too :-)

--
Stefan