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Message-ID: <0fa192d1-b6cc-4a8a-c319-36471cba79e8@allwinnertech.com>
Date:   Mon, 18 Apr 2022 23:08:09 +0800
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Subject: Re: [PATCH] ARM: mmu: fix access to illegal address when using
 earlycon & memblock=debug
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To:     Linus Walleij <linus.walleij@linaro.org>
Cc:     linux@armlinux.org.uk, rmk+kernel@armlinux.org.uk,
        yanfei.xu@windriver.com, ardb@kernel.org, tglx@linutronix.de,
        mirq-linux@rere.qmqm.pl, arnd@arndb.de,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        allwinner-opensource-support@allwinnertech.com
References: <20220316023356.120595-1-victor@allwinnertech.com>
 <CACRpkdabVpD8fQYowCFibdc-r7of6JQnUJAeo0Quqg=cCuOjAQ@mail.gmail.com>
From:   Victor Hassan <victor@allwinnertech.com>
In-Reply-To: <CACRpkdabVpD8fQYowCFibdc-r7of6JQnUJAeo0Quqg=cCuOjAQ@mail.gmail.com>
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On 18/04/2022 07:21, Linus Walleij wrote:
> On Wed, Mar 16, 2022 at 3:33 AM Victor Hassan <victor@allwinnertech.com> wrote:
> 
>> earlycon uses fixmap to create a memory map,
>> So we need to close earlycon before closing fixmap,
>> otherwise printk will access illegal addresses.
>> After creating a new memory map, we open earlycon again.
>>
>> Signed-off-by: Victor Hassan <victor@allwinnertech.com>
> 
> I think noone really noticed this because everyone on Arm systems
> use CONFIG_DEBUG_LL, and that makes printascii hammer out
> stuff on the console very early, it even accounts for whether we have
> MMU on or not.
> 
Hi Linus,
Thank you for the reply. I used earlycon, in early_fixmap_shutdown, the 
base address of earlycon is in the critical stage of release and 
reassignment, so early_fixmap_shutdown -> create_mapping should not call 
earlycon in this process, and create_mapping has a lot of conditions 
that trigger print, memblock=debug just makes it easier to expose problems.

> How are you using this on Arm even? What system and what serial
> driver?
I'm using serial driver 8250 on arm32, with cmdline: memblock=debug.
CONFIG_SERIAL_8250=y
CONFIG_SERIAL_8520_CONSOLE=y
> 
> That said, it looks correct.
> Acked-by: Linus Walleij <linus.walleij@linaro.org>
Thank you.
> 
> Yours,
> Linus Walleij

Sincerely,
Victor Hassan