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@amd.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 ff9520e002be..c61d52420c5f 100644
--- a/drivers/iommu/amd/debugfs.c
+++ b/drivers/iommu/amd/debugfs.c
@@ -15,6 +15,50 @@
 static struct dentry *amd_iommu_debugfs;
 
 #define	MAX_NAME_LEN	20
+#define	OFS_IN_SZ	8
+
+static int mmio_offset = -1;
+
+static ssize_t iommu_mmio_write(struct file *filp, const char __user *ubuf,
+				size_t cnt, loff_t *ppos)
+{
+	struct seq_file *m = filp->private_data;
+	struct amd_iommu *iommu = m->private;
+	int ret;
+
+	mmio_offset = -1;
+
+	if (cnt > OFS_IN_SZ)
+		return -EINVAL;
+
+	ret = kstrtou32_from_user(ubuf, cnt, 0, &mmio_offset);
+	if (ret)
+		return ret;
+
+	if (mmio_offset > iommu->mmio_phys_end - 4) {
+		mmio_offset = -1;
+		return  -EINVAL;
+	}
+
+	return cnt;
+}
+
+static int iommu_mmio_show(struct seq_file *m, void *unused)
+{
+	struct amd_iommu *iommu = m->private;
+	u64 value;
+
+	if (mmio_offset < 0) {
+		seq_puts(m, "Please provide mmio register's offset\n");
+		return 0;
+	}
+
+	value = readq(iommu->mmio_base + mmio_offset);
+	seq_printf(m, "Offset:0x%x Value:0x%016llx\n", mmio_offset, value);
+
+	return 0;
+}
+DEFINE_SHOW_STORE_ATTRIBUTE(iommu_mmio);
 
 void amd_iommu_debugfs_setup(void)
 {
@@ -26,5 +70,8 @@ void amd_iommu_debugfs_setup(void)
 	for_each_iommu(iommu) {
 		snprintf(name, MAX_NAME_LEN, "iommu%02d", iommu->index);
 		iommu->debugfs = debugfs_create_dir(name, amd_iommu_debugfs);
+
+		debugfs_create_file("mmio", 0644, iommu->debugfs, iommu,
+				    &iommu_mmio_fops);
 	}
 }
-- 
2.25.1

Dheeraj,


On 3/17/2025 5:28 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@amd.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 ff9520e002be..c61d52420c5f 100644
> --- a/drivers/iommu/amd/debugfs.c
> +++ b/drivers/iommu/amd/debugfs.c
> @@ -15,6 +15,50 @@
>  static struct dentry *amd_iommu_debugfs;
>  
>  #define	MAX_NAME_LEN	20
> +#define	OFS_IN_SZ	8
> +
> +static int mmio_offset = -1;


Somehow I missed to catch this earlier. Here you have global variable but mmio
is defined per IOMMU. Shouldn't we track it per IOMMU ?

-Vasant

Hi Vasant,

On 3/19/2025 10:20 PM, Vasant Hegde wrote:
> Dheeraj,
> 
> 
> On 3/17/2025 5:28 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@amd.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 ff9520e002be..c61d52420c5f 100644
>> --- a/drivers/iommu/amd/debugfs.c
>> +++ b/drivers/iommu/amd/debugfs.c
>> @@ -15,6 +15,50 @@
>>   static struct dentry *amd_iommu_debugfs;
>>   
>>   #define	MAX_NAME_LEN	20
>> +#define	OFS_IN_SZ	8
>> +
>> +static int mmio_offset = -1;
> 
> 
> Somehow I missed to catch this earlier. Here you have global variable but mmio
> is defined per IOMMU. Shouldn't we track it per IOMMU ?

Yes correct we need to maintain per iommu global variables for mmio and 
capability registers offset. I have sent v5 addressing this. Please find 
some time to review it.

Thanks
Dheeraj

> 
> -Vasant
>