[RFC PATCH] ARM: add fixmap based earlycon support

[Ard Biesheuvel]

(thread is here: http://thread.gmane.org/gmane.linux.ports.arm.kernel/409329)

On 2 May 2015 at 10:37, Ard Biesheuvel <ard.biesheuvel at linaro.org> wrote:
> On 1 May 2015 at 18:18, Russell King - ARM Linux <linux at arm.linux.org.uk> wrote:
>> On Wed, Apr 29, 2015 at 03:51:48PM +0200, Ard Biesheuvel wrote:
>>> This adds support for fixmap based earlycon by moving the fixmap
>>> initialization to an earlier stage and introducing the Kconfig symbol
>>> that wires up the existing code.
>>
>> I don't see the patches for this fixmap based earlycon.  What's the
>> status of those, and how are they getting into mainline?
>>
>
> They are already /in/ mainline. This single patch is all that is
> required to wire it up for ARM.
>
> However, I did notice after sending this that another implementation
> had been proposed already:
> http://lkml.iu.edu/hypermail/linux/kernel/1412.3/00855.html
>
> I am not sure which one is more correct, but the general idea is the
> same, i.e., to allocate the fixmap PTEs from bss rather than the heap.

Anyone else care to comment on this?

DT based earlycon is a *really* useful thing to have if you are
working on early kernel code.
With many of the DTs now having been extended with a
/chosen/stdout-path property, it really only takes a simple 'earlycon'
command line parameter (without any arguments) to get console output
as soon as the early DT scan is concluded. I suppose this is also a
useful thing for multi platform kernels?

BTW the patch still applies to v4.1-rc6

Regards,
Ard.