linux-kernel - Re: [PATCH 5/5] ARM: make ARCH

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Message-Id: <ab221e9a-e504-443f-9713-9a7cc23c66e9@www.fastmail.com>
Date:   Wed, 28 Sep 2022 10:13:35 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Geert Uytterhoeven" <geert@...ux-m68k.org>
Cc:     "Arnd Bergmann" <arnd@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        "Russell King" <linux@...linux.org.uk>,
        "Linus Walleij" <linus.walleij@...aro.org>,
        "Geert Uytterhoeven" <geert+renesas@...der.be>,
        "Krzysztof Kozlowski" <krzysztof.kozlowski@...aro.org>,
        "Ard Biesheuvel" <ardb@...nel.org>, "Sekhar Nori" <nsekhar@...com>,
        "Bartosz Golaszewski" <brgl@...ev.pl>,
        "Shawn Guo" <shawnguo@...nel.org>,
        "Sascha Hauer" <s.hauer@...gutronix.de>,
        "Pengutronix Kernel Team" <kernel@...gutronix.de>,
        "Andrew Lunn" <andrew@...n.ch>,
        "Gregory Clement" <gregory.clement@...tlin.com>,
        "Sebastian Hesselbarth" <sebastian.hesselbarth@...il.com>
Subject: Re: [PATCH 5/5] ARM: make ARCH_MULTIPLATFORM user-visible

On Wed, Sep 28, 2022, at 8:48 AM, Geert Uytterhoeven wrote:
> On Tue, Sep 27, 2022 at 10:19 PM Arnd Bergmann <arnd@...db.de> wrote:
>> On Tue, Sep 27, 2022, at 3:31 PM, Geert Uytterhoeven wrote:
>> > On Thu, Aug 18, 2022 at 4:56 PM Arnd Bergmann <arnd@...nel.org> wrote:
>> >> --- a/arch/arm/Kconfig.debug
>> >> +++ b/arch/arm/Kconfig.debug
>> >> @@ -1904,6 +1904,7 @@ config DEBUG_UART_8250_PALMCHIP
>> >>
>> >>  config DEBUG_UNCOMPRESS
>> >>         bool "Enable decompressor debugging via DEBUG_LL output"
>> >> +       depends on !ARCH_MULTIPLATFORM
>> >
>> > Shouldn't DEBUG_LL itself depend on !ARCH_MULTIPLATFORM instead?
>>
>> That would also be possible, but I prefer to keep limiting only
>> the DEBUG_UNCOMPRESS. The idea of DEBUG_LL is that while it's
>> hardwired to a particular hardware address, it does not actually
>> access this address unless you specify the 'earlyprintk'
>> argument on the command line.
>
> ... or unless something goes really wrong, and the kernel tries to
> inform the user using early_print()?

I don't think this matters either: without DEBUG_LL, you get a non-booting
kernel and no diagnostics, while with DEBUG_LL, you might get some
diagnostic if you have configured the right debug address, and otherwise
the user gets the same as before: a crash without any output ;-)

> Note that the I/O region for the debug serial port is mapped regardless.
> Any chance this can cause conflicts?

Not sure. The early debug mapping should only be used in for
the earlyprintk output, but if a platform has a conflicting mapping
at the same address, it just never gets used before it gets replaced.

     Arnd