linux-kernel - Re: [PATCH v1 0/6] x86/boot: Enable earlyprintk on MMIO (8-bit)

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Message-ID: <db19e81405d17e9eb9a3c1d4798220178e4f9373.camel@infradead.org>
Date: Fri, 02 May 2025 10:33:49 -0700
From: David Woodhouse <dwmw2@...radead.org>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, Ashish Kalra
 <ashish.kalra@....com>, "Kirill A. Shutemov"
 <kirill.shutemov@...ux.intel.com>,  linux-kernel@...r.kernel.org
Cc: 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>, Denis Mukhin
 <dmukhin@...d.com>
Subject: Re: [PATCH v1 0/6] x86/boot: Enable earlyprintk on MMIO (8-bit)

On Fri, 2025-05-02 at 15:29 +0300, Andy Shevchenko wrote:
> Some of the platforms may have no legacy COM ports and only provide
> an MMIO accessible UART. Add support for such to earlyprintk for the
> boot phase of the kernel.

Shiny. I had to hack QEMU's PCI serial port to do unnatural things, in
order to test the mmio32 variant which was the only thing the
earlyprintk code used to support. But I *did* so, and it works with the
kexec debugging.

Can you add support for this mode to the kexec debugging too, please?

I believe it's currently in tip/asm. This should be a simple example to
work from:
https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?h=x86/asm&id=7516e7216bdfb9e2fab0a0ca3bd23cb2e61e46ed

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