1 /*
2  * kmsg dumper that ensures the OPAL console fully flushes panic messages
3  *
4  * Author: Russell Currey <ruscur@russell.cc>
5  *
6  * Copyright 2015 IBM Corporation.
7  *
8  * This program is free software; you can redistribute it and/or modify it
9  * under the terms of the GNU General Public License as published by the
10  * Free Software Foundation; either version 2 of the License, or (at your
11  * option) any later version.
12  */
13 
14 #include <linux/kmsg_dump.h>
15 
16 #include <asm/opal.h>
17 #include <asm/opal-api.h>
18 
19 /*
20  * Console output is controlled by OPAL firmware.  The kernel regularly calls
21  * OPAL_POLL_EVENTS, which flushes some console output.  In a panic state,
22  * however, the kernel no longer calls OPAL_POLL_EVENTS and the panic message
23  * may not be completely printed.  This function does not actually dump the
24  * message, it just ensures that OPAL completely flushes the console buffer.
25  */
26 static void force_opal_console_flush(struct kmsg_dumper *dumper,
27 				     enum kmsg_dump_reason reason)
28 {
29 	int i;
30 	int64_t ret;
31 
32 	/*
33 	 * Outside of a panic context the pollers will continue to run,
34 	 * so we don't need to do any special flushing.
35 	 */
36 	if (reason != KMSG_DUMP_PANIC)
37 		return;
38 
39 	if (opal_check_token(OPAL_CONSOLE_FLUSH)) {
40 		ret = opal_console_flush(0);
41 
42 		if (ret == OPAL_UNSUPPORTED || ret == OPAL_PARAMETER)
43 			return;
44 
45 		/* Incrementally flush until there's nothing left */
46 		while (opal_console_flush(0) != OPAL_SUCCESS);
47 	} else {
48 		/*
49 		 * If OPAL_CONSOLE_FLUSH is not implemented in the firmware,
50 		 * the console can still be flushed by calling the polling
51 		 * function enough times to flush the buffer.  We don't know
52 		 * how much output still needs to be flushed, but we can be
53 		 * generous since the kernel is in panic and doesn't need
54 		 * to do much else.
55 		 */
56 		printk(KERN_NOTICE "opal: OPAL_CONSOLE_FLUSH missing.\n");
57 		for (i = 0; i < 1024; i++) {
58 			opal_poll_events(NULL);
59 		}
60 	}
61 }
62 
63 static struct kmsg_dumper opal_kmsg_dumper = {
64 	.dump = force_opal_console_flush
65 };
66 
67 void __init opal_kmsg_init(void)
68 {
69 	int rc;
70 
71 	/* Add our dumper to the list */
72 	rc = kmsg_dump_register(&opal_kmsg_dumper);
73 	if (rc != 0)
74 		pr_err("opal: kmsg_dump_register failed; returned %d\n", rc);
75 }
76