linux-kernel - Re: [PATCH v7 4/8] x86/kexec: Add 8250 serial port output

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Message-ID: <Z9K0-CFdaBkptAJR@gmail.com>
Date: Thu, 13 Mar 2025 11:35:36 +0100
From: Ingo Molnar <mingo@...nel.org>
To: David Woodhouse <dwmw2@...radead.org>
Cc: kexec@...ts.infradead.org, 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>,
	David Woodhouse <dwmw@...zon.co.uk>,
	"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
	Kai Huang <kai.huang@...el.com>,
	Nikolay Borisov <nik.borisov@...e.com>,
	linux-kernel@...r.kernel.org, Simon Horman <horms@...nel.org>,
	Dave Young <dyoung@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>, jpoimboe@...nel.org,
	bsz@...zon.de
Subject: Re: [PATCH v7 4/8] x86/kexec: Add 8250 serial port output

* David Woodhouse <dwmw2@...radead.org> wrote:

> From: David Woodhouse <dwmw@...zon.co.uk>
> 
> If a serial port was configured for early_printk, use it for debug output
> from the relocate_kernel exception handler too.

Does the early console output something once it's initialized? If not 
then I'd go one step further here: if early_printk serial debugging was 
configured, let's output some sort of message as early as it's expected 
to work. That way if any of this debug codepath regresses for 
relocate_kernel, the discovery of that regression won't be delayed 
until something nasty triggers within relocate_kernel that would 
necessitate a working debug mechanism ...

Also, printing something to the early console using these new 
relocate_kernel printing functions would be an additional bonus as 
well, for similar reasons.

Thanks,

	Ingo