Device id user input is needed for dumping IOMMU data structures like
device table, IRT etc in AMD IOMMU debugfs.

eg.
1. # echo 0000:01:00.0 > /sys/kernel/debug/iommu/amd/devid
   # cat /sys/kernel/debug/iommu/amd/devid
   Output : 0000:01:00.0

2. # echo 01:00.0 > /sys/kernel/debug/iommu/amd/devid
   # cat /sys/kernel/debug/iommu/amd/devid
   Output : 0000:01:00.0

Signed-off-by: Dheeraj Kumar Srivastava <dheerajkumar.srivastava@amd.com>
---
 drivers/iommu/amd/debugfs.c | 78 +++++++++++++++++++++++++++++++++++++
 1 file changed, 78 insertions(+)

diff --git a/drivers/iommu/amd/debugfs.c b/drivers/iommu/amd/debugfs.c
index 1b989d45257f..74c88a80c6d0 100644
--- a/drivers/iommu/amd/debugfs.c
+++ b/drivers/iommu/amd/debugfs.c
@@ -16,9 +16,11 @@ static struct dentry *amd_iommu_debugfs;
 
 #define	MAX_NAME_LEN	20
 #define	OFS_IN_SZ	8
+#define	DEVID_IN_SZ	16
 
 static int mmio_offset = -1;
 static int cap_offset = -1;
+static int sbdf = -1;
 
 static ssize_t iommu_mmio_write(struct file *filp, const char __user *ubuf,
 				size_t cnt, loff_t *ppos)
@@ -149,6 +151,80 @@ static int iommu_cmdbuf_show(struct seq_file *m, void *unused)
 }
 DEFINE_SHOW_ATTRIBUTE(iommu_cmdbuf);
 
+static ssize_t devid_write(struct file *filp, const char __user *ubuf,
+			   size_t cnt, loff_t *ppos)
+{
+	struct amd_iommu_pci_seg *pci_seg;
+	int seg, bus, slot, func;
+	struct amd_iommu *iommu;
+	char *srcid_ptr;
+	u16 devid;
+	int i;
+
+	sbdf = -1;
+
+	if (cnt >= DEVID_IN_SZ)
+		return -EINVAL;
+
+	srcid_ptr = memdup_user_nul(ubuf, cnt);
+	if (IS_ERR(srcid_ptr))
+		return PTR_ERR(srcid_ptr);
+
+	i = sscanf(srcid_ptr, "%x:%x:%x.%x", &seg, &bus, &slot, &func);
+	if (i != 4) {
+		i = sscanf(srcid_ptr, "%x:%x.%x", &bus, &slot, &func);
+		if (i != 3) {
+			kfree(srcid_ptr);
+			return -EINVAL;
+		}
+		seg = 0;
+	}
+
+	devid = PCI_DEVID(bus, PCI_DEVFN(slot, func));
+
+	/* Check if user device id input is a valid input */
+	for_each_pci_segment(pci_seg) {
+		if (pci_seg->id != seg)
+			continue;
+		if (devid > pci_seg->last_bdf) {
+			kfree(srcid_ptr);
+			return -EINVAL;
+		}
+		iommu = pci_seg->rlookup_table[devid];
+		if (!iommu) {
+			kfree(srcid_ptr);
+			return -ENODEV;
+		}
+		break;
+	}
+
+	if (pci_seg->id != seg) {
+		kfree(srcid_ptr);
+		return -EINVAL;
+	}
+
+	sbdf = PCI_SEG_DEVID_TO_SBDF(seg, devid);
+
+	kfree(srcid_ptr);
+
+	return cnt;
+}
+
+static int devid_show(struct seq_file *m, void *unused)
+{
+	u16 devid;
+
+	if (sbdf >= 0) {
+		devid = PCI_SBDF_TO_DEVID(sbdf);
+		seq_printf(m, "%04x:%02x:%02x:%x\n", PCI_SBDF_TO_SEGID(sbdf),
+			   PCI_BUS_NUM(devid), PCI_SLOT(devid), PCI_FUNC(devid));
+	} else
+		seq_puts(m, "No or Invalid input provided\n");
+
+	return 0;
+}
+DEFINE_SHOW_STORE_ATTRIBUTE(devid);
+
 void amd_iommu_debugfs_setup(void)
 {
 	struct amd_iommu *iommu;
@@ -171,4 +247,6 @@ void amd_iommu_debugfs_setup(void)
 		debugfs_create_file("cmdbuf", 0444, iommu->debugfs, iommu,
 				    &iommu_cmdbuf_fops);
 	}
+	debugfs_create_file("devid", 0644, amd_iommu_debugfs, NULL,
+			    &devid_fops);
 }
-- 
2.25.1