Re: [PATCH 3/5] tty: serial: sh-sci: Hide earlycon config question

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Rob,

On Wed, May 2, 2018 at 4:32 AM, Rob Herring <robherring2@gmail.com> wrote:
> On Sun, Apr 15, 2018 at 2:09 PM, Rich Felker <dalias@libc.org> wrote:
>> On Sun, Apr 15, 2018 at 08:58:42PM +0200, Geert Uytterhoeven wrote:
>>> On Sun, Apr 15, 2018 at 2:34 AM, Rich Felker <dalias@libc.org> wrote:
>>> > On Thu, Nov 30, 2017 at 02:12:00PM +0100, Geert Uytterhoeven wrote:
>>> >> Renesas H8/300 and ARM platforms use DT and support earlycon, so most
>>> >> users want earlycon support to be enabled.
>>> >>
>>> >> On SuperH platforms, earlycon is not yet supported.
>>> >>
>>> >> Hence follow the above rationale to configure the default, unless
>>> >> CONFIG_EXPERT is enabled.
>>> >>
>>> >> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
>>> >> ---
>>> >>  drivers/tty/serial/Kconfig | 3 ++-
>>> >>  1 file changed, 2 insertions(+), 1 deletion(-)
>>> >>
>>> >> diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
>>> >> index 0c75562d620feb82..952a2c6a9da08fdd 100644
>>> >> --- a/drivers/tty/serial/Kconfig
>>> >> +++ b/drivers/tty/serial/Kconfig
>>> >> @@ -774,10 +774,11 @@ config SERIAL_SH_SCI_CONSOLE
>>> >>       default y
>>> >>
>>> >>  config SERIAL_SH_SCI_EARLYCON
>>> >> -     bool "Support for early console on SuperH SCI(F)"
>>> >> +     bool "Support for early console on SuperH SCI(F)" if EXPERT
>>> >>       depends on SERIAL_SH_SCI=y
>>> >>       select SERIAL_CORE_CONSOLE
>>> >>       select SERIAL_EARLYCON
>>> >> +     default ARCH_RENESAS || H8300
>>> >>
>>> >>  config SERIAL_SH_SCI_DMA
>>> >>       bool "DMA support"
>>> >> --
>>> >
>>> > Can you clarify what the claim that SuperH does not support earlycon
>>> > is based on? My understanding is that users were successfully using
>>> > this option on Renesas SH systems, and I'm using it on J2 with the
>>> > uartlite earlycon support which I added in 7cdcc29e49. I think if you
>>> > want to omit the question it should always default to enabled.
>>>
>>> This is a patch for a Kconfig option for the Renesas sh-sci driver, which
>>> supports the SCI, SCIF, SCIFA, SCIFB, and HSCIF uarts found on various
>>> Renesas SoCs.
>>>
>>> Earlycon is used with DT only. While you are using earlycon on J2, you do
>>> use it with a different uart (uartlite). Currently there's no upstream support
>>> for using DT on Renesas SuperH SoCs. If this changes, the default for
>>> SERIAL_SH_SCI_EARLYCON has to be changed.
>>>
>>> So none of my patch applies to the current state of SuperH Linux support.
>>
>> OK, I was under the impression (from users) that it worked on Renesas
>> SH devices without DT. If it really doesn't then it doesn't matter
>> until DT support for them is added. I've got some hardware to
>> experiment with now so I'll see what can be done.
>
> Yes, it works without DT (but maybe that is UART specific). It was
> originally an x86 8250 thing.
>
> The main thing you need is either fixmap support or ioremap has to
> work before paging_init when early_params are processed.

Without DT and its chosen/stdout-path, you need a way to specify which
UART to use. That's typically done through a UART-specific earlyconextension.

The sh-sci.c driver uses:

    OF_EARLYCON_DECLARE(scif, "renesas,scif", scif_early_console_setup);
    (+ for sci, scifa, scifb, hscif)

So it may actually work with earlycon=scif,0x<addr>?

Anyone who can try on a non-DT SH system?

if it works, the default should be changed to

    default ARCH_RENESAS || H8300 || SUPERH

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds