linux-kernel - Re: [PATCH 1/2] arm64: change ARCH

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Date:   Mon, 9 Mar 2020 11:32:06 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Chunyan Zhang <zhang.lyra@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Jiri Slaby <jslaby@...e.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Chunyan Zhang <chunyan.zhang@...soc.com>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        Baolin Wang <baolin.wang7@...il.com>,
        Orson Zhai <orsonzhai@...il.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Android Kernel Team <kernel-team@...roid.com>
Subject: Re: [PATCH 1/2] arm64: change ARCH_SPRD Kconfig to tristate

Hi Chunyan,

On Mon, Mar 9, 2020 at 9:32 AM Chunyan Zhang <zhang.lyra@...il.com> wrote:
> On Mon, 9 Mar 2020 at 16:03, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> > On Thu, Mar 5, 2020 at 11:33 AM Chunyan Zhang <zhang.lyra@...il.com> wrote:
> > > From: Chunyan Zhang <chunyan.zhang@...soc.com>
> > >
> > > 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@...soc.com>
> >
> > 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.
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@...ux-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