[PATCH] arm64: add support for uart earlyprintk

[Anup Patel]

On Thu, Feb 28, 2013 at 9:01 PM, Catalin Marinas
<catalin.marinas at arm.com> wrote:
> On Thu, Feb 28, 2013 at 02:06:27PM +0000, Anup Patel wrote:
>> On Thu, Feb 28, 2013 at 6:22 PM, Marc Zyngier <marc.zyngier at arm.com> wrote:
>> > On 28/02/13 12:10, Catalin Marinas wrote:
>> >> On Thu, Feb 28, 2013 at 11:34:17AM +0000, Marc Zyngier wrote:
>> >>> On 28/02/13 11:01, Anup Patel wrote:
>> >>>> +}
>> >>>> +
>> >>>> +/*
>> >>>>   * PL011 single character TX.
>> >>>>   */
>> >>>>  static void pl011_printch(char ch)
>> >>>> @@ -47,6 +62,7 @@ struct earlycon_match {
>> >>>>
>> >>>>  static const struct earlycon_match earlycon_match[] __initconst = {
>> >>>>     { .name = "pl011", .printch = pl011_printch, },
>> >>>> +   { .name = "uart", .printch = uart_printch, },
>> >>>
>> >>> "uart" is way too generic. pl011 is an UART too, and I suspect most of
>> >>> the backends that are going to be added here over time will be UARTs.
>> >>>
>> >>> "uart8250" would be a possibility (and actually consistent with the rest
>> >>> of the kernel, see drivers/tty/serial/8250/8250_early.c.
>> >>
>> >> I think it makes more sense to use the existing 8250_early.c driver. It
>> >> has more features than the simple earlyprintk implementation in the
>> >> 64-bit kernel (like parsing more parameters, initialising the UART). The
>> >> only difference is that the early_param is called "earlycon".
>> >
>> > Indeed, this seems to be the best way, as it removes the need for this
>> > patch altogether.
>>
>> The earlycon option does not seem to work on my ARM64 kernel because it uses
>> ioremap_nocache() whereas ARM64 earlyprintk uses early_io_map()
>
> We try to get earlyprintk as early as possible and ioremap() isn't
> available yet, hence the arm64-specific early_io_map(). It looks like
> x86 has a CONFIG_FIX_EARLYCON_MEM to avoid the ioremap() issue but I
> wouldn't add yet another option for arm64.
>
> So we can go with your arm64 patch, once you implement the feedback from
> Marc.
>
> --
> Catalin

Sure, I will incorporate Marc's comments and resend the patch with
more appropriate
subject and description.

Regards,
Anup
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