linux-kernel - Re: Problem with nbcon console and amba-pl011 serial port

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Message-Id: <20250603090313.126850-1-ryotkkr98@gmail.com>
Date: Tue,  3 Jun 2025 18:03:13 +0900
From: Ryo Takakura <ryotkkr98@...il.com>
To: mhklinux@...look.com
Cc: fj6611ie@...jp.fujitsu.com,
	gregkh@...uxfoundation.org,
	jirislaby@...nel.org,
	john.ogness@...utronix.de,
	pmladek@...e.com,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org,
	linux@...linux.org.uk
Subject: Re: Problem with nbcon console and amba-pl011 serial port

Hi!

On Tue, 3 Jun 2025 03:18:23 +0000, Michael Kelley wrote:
>The problem is timing dependent.  In some cases, the "pr/ttyAMA0"
>thread is evidently able to get the message out before panic() calls
>pr_emerg(). In my case running as a guest on Hyper-V, the pl011 device
>in the guest VM is emulated by Hyper-V. Each pl011 register access
>traps to the hypervisor, which slows things down and probably makes
>the problem more likely. But from what I can see, the underlying
>race condition exists regardless.

I believe the issue is not amba-pl011 specific, so maybe John and Petr
better be Cced as well.

Sincerely,
Ryo Takakura