[PATCH] arm64: add support for uart earlyprintk

[Anup Patel]

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()

I do agree that earlycon is more feature rich compared to ARM64 earlyprintk but
I doubt whether 8250_early.c is generic enough to be usable on ARM64 kernel

The best part about ARM64 earlyprintk is that its very very simple and does not
expect us to re-programme UART HW which is already programmed by the
the bootloader.

IMHO, adding 8250 support in ARM64 earlyprintk would be very ARM64
specific and not
re-implementation of 8250_early.c

>
>         M.
> --
> Jazz is not dead. It just smells funny...
>

Regards,
Anup
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