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

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Message-ID: <CA+H2tpEzFAbfzMuUGMfW3BqCKv2+kk+cLL5gWpR-zJZFYwWKqw@mail.gmail.com>
Date:   Tue, 10 Mar 2020 17:41:14 +0800
From:   Orson Zhai <orsonzhai@...il.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Chunyan Zhang <zhang.lyra@...il.com>,
        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>,
        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 Geert,

On Mon, Mar 9, 2020 at 6:32 PM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>
> 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.

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@...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