linux-kernel - Re: [PATCH] iommu/amd: Enhance "Completion-wait Time-out" error message

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Message-ID: <5uof463yi5zq6y3rsjqdifktvqxe4ctb63koz4qgbwvjgiudlg@qtjxrrymt3mj>
Date: Wed, 29 Oct 2025 09:30:07 +0100
From: Jörg Rödel <joro@...tes.org>
To: Vasant Hegde <vasant.hegde@....com>
Cc: Dheeraj Kumar Srivastava <dheerajkumar.srivastava@....com>, 
	will@...nel.org, robin.murphy@....com, iommu@...ts.linux.dev, 
	linux-kernel@...r.kernel.org, suravee.suthikulpanit@....com, Santosh.Shukla@....com
Subject: Re: [PATCH] iommu/amd: Enhance "Completion-wait Time-out" error
 message

On Tue, Oct 28, 2025 at 02:45:16PM +0530, Vasant Hegde wrote:
> We have debugfs support to extract entire command buffer. Also many cases once
> we hit completion wait timeout, buffer won't progress.. and we will hit
> completion wait repetitively. Hence in V2 he has removed printing entire command
> buffer.
> 
> Do you want to log entire buffer once to dmesg if amd_iommu_dump=1 ? (for first
> completion wait timeout event).

I think there is some value in printing the command buffer contents at the
point in time when the timeout happens. When it is read later from debug-fs,
the state of the command buffer might already be different, making debugging
harder.

Although dmesg is not the optimal place to dump this information, I also do not
see a better place.

Regards,

	Joerg