linux-kernel - Re: [PATCH v6 6/8] iommu/amd: Add debugfs support to dump device table

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Message-ID: <5b360e8a-03bf-4886-8134-8e4ab5a9f485@amd.com>
Date: Sun, 29 Jun 2025 11:08:43 +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 6/8] iommu/amd: Add debugfs support to dump device
 table

Dheeraj,


On 6/4/2025 10:06 PM, Dheeraj Kumar Srivastava wrote:
> IOMMU uses device table data structure to get per-device information for
> DMA remapping, interrupt remapping, and other functionalities. It's a
> valuable data structure to visualize for debugging issues related to
> IOMMU.
> 
> eg.
> -> To dump device table entry for a particular device
>    #echo 0000:c4:00.0 > /sys/kernel/debug/iommu/amd/devid
>    #cat /sys/kernel/debug/iommu/amd/devtbl
> 
>    or
> 
>    #echo c4:00.0 > /sys/kernel/debug/iommu/amd/devid
>    #cat /sys/kernel/debug/iommu/amd/devtbl
> 
> Signed-off-by: Dheeraj Kumar Srivastava <dheerajkumar.srivastava@....com>
> ---
>  drivers/iommu/amd/debugfs.c | 49 +++++++++++++++++++++++++++++++++++++
>  1 file changed, 49 insertions(+)
> 
> diff --git a/drivers/iommu/amd/debugfs.c b/drivers/iommu/amd/debugfs.c
> index 8b57ab4ab809..38d3cab5fd8d 100644
> --- a/drivers/iommu/amd/debugfs.c
> +++ b/drivers/iommu/amd/debugfs.c
> @@ -207,6 +207,53 @@ static int devid_show(struct seq_file *m, void *unused)
>  }
>  DEFINE_SHOW_STORE_ATTRIBUTE(devid);
>  
> +static void dump_dte(struct seq_file *m, struct amd_iommu_pci_seg *pci_seg, u16 devid)
> +{
> +	struct dev_table_entry *dev_table;
> +	struct amd_iommu *iommu;
> +
> +	iommu = pci_seg->rlookup_table[devid];
> +	if (!iommu)
> +		return;
> +
> +	dev_table = get_dev_table(iommu);
> +	if (!dev_table) {
> +		seq_puts(m, "Device table not found");
> +		return;
> +	}
> +
> +	seq_printf(m, "%-12s %16s %16s %16s %16s iommu\n", "DeviceId",
> +		   "QWORD[3]", "QWORD[2]", "QWORD[1]", "QWORD[0]");
> +	seq_printf(m, "%04x:%02x:%02x.%x ", pci_seg->id, PCI_BUS_NUM(devid),
> +		   PCI_SLOT(devid), PCI_FUNC(devid));
> +	for (int i = 3; i >= 0; --i)
> +		seq_printf(m, "%016llx ", dev_table[devid].data[i]);
> +	seq_printf(m, "iommu%d\n", iommu->index);
> +}
> +
> +static int iommu_devtbl_show(struct seq_file *m, void *unused)
> +{
> +	struct amd_iommu_pci_seg *pci_seg;
> +	u16 seg, devid;
> +
> +	if (sbdf < 0) {
> +		seq_puts(m, "Please provide valid device id input\n");

Where? This should clearly indicate where to provide device id.


-Vasant