Re: [PATCH 1/2] arm64: change ARCH_SPRD Kconfig to tristate

[Orson Zhai]

Hi Geert,

On Mon, Mar 9, 2020 at 6:32 PM Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote:
>
> Hi Chunyan,
>
> On Mon, Mar 9, 2020 at 9:32 AM Chunyan Zhang <zhang.lyra@xxxxxxxxx> wrote:
> > On Mon, 9 Mar 2020 at 16:03, Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote:
> > > On Thu, Mar 5, 2020 at 11:33 AM Chunyan Zhang <zhang.lyra@xxxxxxxxx> wrote:
> > > > From: Chunyan Zhang <chunyan.zhang@xxxxxxxxxx>
> > > >
> > > > The default value of Kconfig for almost all sprd drivers are the same with
> > > > ARCH_SPRD, making these drivers built as modules as default would be easier
> > > > if we can set ARCH_SPRD as 'm', so this patch change ARCH_SPRD to tristate.
> > > >
> > > > Signed-off-by: Chunyan Zhang <chunyan.zhang@xxxxxxxxxx>
> > >
> > > Can you actually boot a kernel on a Spreadtrum platform when all platform
> > > and driver support is modular?
> >
> > Yes, even if all drivers are modular.
>
> Cool. No hard dependencies on e.g. regulators that are turned off when
> unused?
>
> > But I hope serial can be builtin, then I can have a console to see
> > kernel output before loading modules.
>
> No dependency on the clock driver?
> Oh, I see you have a hack in the serial driver, to assume default
> values when the serial port's parent clock is not found.  That may
> limit use of the other serial ports, depending on the actual serial
> hardware.

There is an function named "sprd_uart_is_console()" in the driver
code. So the hack could be only applied when the
port is identified as console. And other ports might return
PROBE_DEFER until the clock is ready.

Could it work out of the limitation?

-Orson

> And on Sharkl64, the serial port's clock is a fixed-clock anyway, so
> you don't even need the hack.
>
> But in general you cannot rely on that, especially if your SoC has clock
> and/or power domains.
>
> BTW, what about the watchdog driver? That one does need a clock, and
> loading it too late will reboot your system.
>
> > Also, this's what Google GKI [1] asked :)
> >
> > Regards,
> > Chunyan
> >
> > [1] https://arstechnica.com/gadgets/2019/11/google-outlines-plans-for-mainline-linux-kernel-support-in-android/
>
> Let's see how having everything modular works out on an SoC where all
> hardware is part of a clock and power domain.
>
> Thanks!
>
> Gr{oetje,eeting}s,
>
>                         Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
>
> 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