scsi: hisi_sas: Add latest_dump for the debugfs dump

Before that, after the user triggers the dump, the latest dump
information can be viewed in the directory with the maximum number in
the dump directory.

After this series patch, the driver creates all debugfs directories and
files during initialization. Therefore, users cannot know the directory
where the latest dump information is stored. So, add latest_dump file to
notify users where the latest dump information is stored.

Signed-off-by: Yihang Li <liyihang9@huawei.com>
Link: https://lore.kernel.org/r/20241008021822.2617339-14-liyihang9@huawei.com
Reviewed-by: Xingui Yang <yangxingui@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

Author: Yihang Li

drivers/scsi/hisi_sas/hisi_sas_v3_hw.c

@@ -4814,13 +4814,30 @@ static void debugfs_bist_init_v3_hw(struct hisi_hba *hisi_hba)
 	hisi_hba->debugfs_bist_linkrate = SAS_LINK_RATE_1_5_GBPS;
 }
 
+static int debugfs_dump_index_v3_hw_show(struct seq_file *s, void *p)
+{
+	int *debugfs_dump_index = s->private;
+
+	if (*debugfs_dump_index > 0)
+		seq_printf(s, "%d\n", *debugfs_dump_index - 1);
+	else
+		seq_puts(s, "dump not triggered\n");
+
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(debugfs_dump_index_v3_hw);
+
 static void debugfs_dump_init_v3_hw(struct hisi_hba *hisi_hba)
 {
 	int i;
 
 	hisi_hba->debugfs_dump_dentry =
 			debugfs_create_dir("dump", hisi_hba->debugfs_dir);
 
+	debugfs_create_file("latest_dump", 0400, hisi_hba->debugfs_dump_dentry,
+			    &hisi_hba->debugfs_dump_index,
+			    &debugfs_dump_index_v3_hw_fops);
+
 	for (i = 0; i < hisi_sas_debugfs_dump_count; i++)
 		debugfs_create_files_v3_hw(hisi_hba, i);
 }