scsi: hisi_sas: Limit users changing debugfs BIST count value

Add a file operation for "cnt" file under bist directory, so users can only
read "cnt" or clear "cnt" to zero, but cannot randomly modify.

Link: https://lore.kernel.org/r/1645703489-87194-6-git-send-email-john.garry@huawei.comSigned-off-by: Xiang Chen <chenxiang66@hisilicon.com>
Signed-off-by: Qi Liu <liuqi115@huawei.com>
Signed-off-by: John Garry <john.garry@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/hisi_sas/hisi_sas_v3_hw.c

@@ -3975,6 +3975,54 @@ static const struct file_operations debugfs_bist_phy_v3_hw_fops = {
 	.owner = THIS_MODULE,
 };
 
+static ssize_t debugfs_bist_cnt_v3_hw_write(struct file *filp,
+					const char __user *buf,
+					size_t count, loff_t *ppos)
+{
+	struct seq_file *m = filp->private_data;
+	struct hisi_hba *hisi_hba = m->private;
+	unsigned int cnt;
+	int val;
+
+	if (hisi_hba->debugfs_bist_enable)
+		return -EPERM;
+
+	val = kstrtouint_from_user(buf, count, 0, &cnt);
+	if (val)
+		return val;
+
+	if (cnt)
+		return -EINVAL;
+
+	hisi_hba->debugfs_bist_cnt = 0;
+	return count;
+}
+
+static int debugfs_bist_cnt_v3_hw_show(struct seq_file *s, void *p)
+{
+	struct hisi_hba *hisi_hba = s->private;
+
+	seq_printf(s, "%u\n", hisi_hba->debugfs_bist_cnt);
+
+	return 0;
+}
+
+static int debugfs_bist_cnt_v3_hw_open(struct inode *inode,
+					  struct file *filp)
+{
+	return single_open(filp, debugfs_bist_cnt_v3_hw_show,
+			   inode->i_private);
+}
+
+static const struct file_operations debugfs_bist_cnt_v3_hw_ops = {
+	.open = debugfs_bist_cnt_v3_hw_open,
+	.read = seq_read,
+	.write = debugfs_bist_cnt_v3_hw_write,
+	.llseek = seq_lseek,
+	.release = single_release,
+	.owner = THIS_MODULE,
+};
+
 static const struct {
 	int		value;
 	char		*name;
@@ -4612,8 +4660,8 @@ static void debugfs_bist_init_v3_hw(struct hisi_hba *hisi_hba)
 	debugfs_create_file("phy_id", 0600, hisi_hba->debugfs_bist_dentry,
 			    hisi_hba, &debugfs_bist_phy_v3_hw_fops);
 
-	debugfs_create_u32("cnt", 0600, hisi_hba->debugfs_bist_dentry,
-			   &hisi_hba->debugfs_bist_cnt);
+	debugfs_create_file("cnt", 0600, hisi_hba->debugfs_bist_dentry,
+			    hisi_hba, &debugfs_bist_cnt_v3_hw_ops);
 
 	debugfs_create_file("loopback_mode", 0600,
 			    hisi_hba->debugfs_bist_dentry,