linux-kernel - Re: [PATCH v6 2/8] iommu/amd: Add debugfs support to dump IOMMU MMIO registers

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Message-ID: <5ff3f926-b57a-4fd0-ab75-52e82373c422@amd.com>
Date: Sun, 29 Jun 2025 11:16:20 +0530
From: Vasant Hegde <vasant.hegde@....com>
To: Dheeraj Kumar Srivastava <dheerajkumar.srivastava@....com>,
 joro@...tes.org, suravee.suthikulpanit@....com, will@...nel.org,
 robin.murphy@....com, linux-kernel@...r.kernel.org, iommu@...ts.linux.dev
Subject: Re: [PATCH v6 2/8] iommu/amd: Add debugfs support to dump IOMMU MMIO
 registers



On 6/4/2025 10:06 PM, Dheeraj Kumar Srivastava wrote:
> Analyzing IOMMU MMIO registers gives a view of what IOMMU is
> configured with on the system and is helpful to debug issues
> with IOMMU.
> 
> eg.
> -> To get mmio registers value at offset 0x18 for iommu<x> (say, iommu00)
>    # echo "0x18" > /sys/kernel/debug/iommu/amd/iommu00/mmio
>    # cat /sys/kernel/debug/iommu/amd/iommu00/mmio
> 
> Signed-off-by: Dheeraj Kumar Srivastava <dheerajkumar.srivastava@....com>
> ---
>  drivers/iommu/amd/amd_iommu_types.h |  1 +
>  drivers/iommu/amd/debugfs.c         | 47 +++++++++++++++++++++++++++++
>  2 files changed, 48 insertions(+)
> 
> diff --git a/drivers/iommu/amd/amd_iommu_types.h b/drivers/iommu/amd/amd_iommu_types.h
> index 5089b58e528a..38eca75f6ef1 100644
> --- a/drivers/iommu/amd/amd_iommu_types.h
> +++ b/drivers/iommu/amd/amd_iommu_types.h
> @@ -796,6 +796,7 @@ struct amd_iommu {
>  #ifdef CONFIG_AMD_IOMMU_DEBUGFS
>  	/* DebugFS Info */
>  	struct dentry *debugfs;
> +	int mmio_offset;

This is covered under DEBUGFS config. So this is fine.. but its nice if you
rename the variable such that it indicates its usage.

-Vasant