[PATCH v3 2/8] iommu/amd: Add debugfs support to dump IOMMU MMIO registers

Dheeraj Kumar Srivastava
2025-02-06T06:01:02Z

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.
1. To get mmio registers value for iommu<x>
# 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 | 45 +++++++++++++++++++++++++++++++++++++
1 file changed, 45 insertions(+)

diff --git a/drivers/iommu/amd/debugfs.c b/drivers/iommu/amd/debugfs.c
index ff9520e002be..b16b62ae7111 100644
--- a/drivers/iommu/amd/debugfs.c
+++ b/drivers/iommu/amd/debugfs.c
@@ -15,6 +15,48 @@
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;
+
+ 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;
+ u32 value;
+
+ if (mmio_offset < 0) {
+ seq_puts(m, "Please provide mmio register's offset\n");
+ return 0;
+ }
+
+ value = readl(iommu->mmio_base + mmio_offset);
+ seq_printf(m, "Offset:0x%x Value:0x%08x\n", mmio_offset, value);
+
+ return 0;
+}
+DEFINE_SHOW_STORE_ATTRIBUTE(iommu_mmio);

void amd_iommu_debugfs_setup(void)
{
@@ -26,5 +68,8 @@ 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