linux-kernel - Re: [PATCH v2] x86/early_printk: add MMIO-based UARTs

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Message-ID: <wlidpR0nAfMoUkVTrtOogcSBeZ8pEKU32ZCubunTj3-kDUj4hKY0fJAAQD11aFA5xkGAH9qV2tNee7yB5qJof_lq9zxdXAfzR0Fm6mf5cqI=@proton.me>
Date: Tue, 18 Mar 2025 23:39:41 +0000
From: Denis Mukhin <dmkhn@...ton.me>
To: Ingo Molnar <mingo@...nel.org>
Cc: dmukhin@...d.com, Jonathan Corbet <corbet@....net>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] x86/early_printk: add MMIO-based UARTs

Hi,

Thanks for taking a look!

On Monday, March 17th, 2025 at 12:58 AM, Ingo Molnar <mingo@...nel.org> wrote:

>
>
>
> * Denis Mukhin via B4 Relay devnull+dmukhin.ford.com@...nel.org wrote:
>
> > + if (!strncmp(s, "nocfg", 5))
> > + baudrate = 0;
> > + else {
> > + baudrate = simple_strtoul(s, &e, 0);
> > + if (baudrate == 0 || s == e)
> > + baudrate = DEFAULT_BAUD;
> > + }
>
>
> In standard kernel coding style we always balance curly braces and
> don't skip them in the single-statement case. Ie. the above should be:
>
> if (!strncmp(s, "nocfg", 5)) {
> baudrate = 0;
> } else {
>
> > + if (baudrate)
> > + early_serial_hw_init(115200 / baudrate);
>
>
> Hm, I think that division will go poorly if 'baudrate' ends up being 0
> in the 'nocfg' case ... ;-)

This patch has a guardrail:
  early_serial_hw_init(115200 / baudrate);
will not be called in case of baudrate is 0.

I can re-write code to avoid confusion.

>
> Thanks,
>
> Ingo

Thanks,
Denis