linux-kernel - Re: [PATCH v3 3/8] iommu/amd: Add debugfs support to dump IOMMU Capability registers

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Message-ID: <fbb7d901-25b6-49c7-abeb-4e76451c197f@amd.com>
Date: Thu, 13 Mar 2025 16:02:45 +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 v3 3/8] iommu/amd: Add debugfs support to dump IOMMU
 Capability registers

Dheeraj,


On 2/6/2025 11:29 AM, Dheeraj Kumar Srivastava wrote:
> IOMMU Capability registers defines capabilities of IOMMU and information
> needed for initialising MMIO registers and device table. This is useful
> to dump these registers for debugging IOMMU related issues.
> 
> e.g.To get capability registers value for iommu<x>
>   # echo "0x10" > /sys/kernel/debug/iommu/amd/iommu00/capability
>   # cat /sys/kernel/debug/iommu/amd/iommu00/capability
> 
> Signed-off-by: Dheeraj Kumar Srivastava <dheerajkumar.srivastava@....com>
> ---
>  drivers/iommu/amd/debugfs.c | 47 +++++++++++++++++++++++++++++++++++++
>  1 file changed, 47 insertions(+)
> 
> diff --git a/drivers/iommu/amd/debugfs.c b/drivers/iommu/amd/debugfs.c
> index b16b62ae7111..dc5fdc905754 100644
> --- a/drivers/iommu/amd/debugfs.c
> +++ b/drivers/iommu/amd/debugfs.c
> @@ -18,6 +18,7 @@ static struct dentry *amd_iommu_debugfs;
>  #define	OFS_IN_SZ	8
>  
>  static int mmio_offset = -1;
> +static int cap_offset = -1;
>  
>  static ssize_t iommu_mmio_write(struct file *filp, const char __user *ubuf,
>  				size_t cnt, loff_t *ppos)
> @@ -58,6 +59,50 @@ static int iommu_mmio_show(struct seq_file *m, void *unused)
>  }
>  DEFINE_SHOW_STORE_ATTRIBUTE(iommu_mmio);
>  
> +static ssize_t iommu_capability_write(struct file *filp, const char __user *ubuf,
> +				      size_t cnt, loff_t *ppos)
> +{
> +	int ret;
> +
> +	if (cnt > OFS_IN_SZ)
> +		return -EINVAL;
> +
> +	ret = kstrtou32_from_user(ubuf, cnt, 0, &cap_offset);
> +	if (ret)
> +		return ret;
> +
> +	/* Capability register at offset 0x14 is the last IOMMU capability register. */
> +	if (cap_offset > 0x14) {
> +		cap_offset = -1;
> +		return -EINVAL;
> +	}
> +
> +	return cnt;
> +}
> +
> +static int iommu_capability_show(struct seq_file *m, void *unused)
> +{
> +	struct amd_iommu *iommu = m->private;
> +	u32 value;
> +	int err;
> +
> +	if (cap_offset < 0) {
> +		seq_puts(m, "Please provide capability register's offset\n");

May be you can add last offset details... so that it becomes easy to find out
the offset range.

-Vasant