s390/boot: Add bootdebug option to control debug messages

Suppress decompressor debug messages by default, similar to regular
kernel debug messages that require 'DEBUG' or 'dyndbg' to be enabled
(depending on CONFIG_DYNAMIC_DEBUG). Introduce a 'bootdebug' option to
enable printing these messages when needed.

All messages are still stored in the boot ring buffer regardless.

To enable boot debug messages:

  bootdebug debug

Or combine with 'earlyprintk' to print them without delay:

  bootdebug debug earlyprintk

Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

1 files changed, 8 insertions, 2 deletions

diff --git a/arch/s390/kernel/setup.c b/arch/s390/kernel/setup.c
index feff1bb9ac2d..dd0979182890 100644
--- a/arch/s390/kernel/setup.c
+++ b/arch/s390/kernel/setup.c
@@ -160,6 +160,7 @@ struct oldmem_data __bootdata_preserved(oldmem_data);
 char __bootdata(boot_rb)[PAGE_SIZE * 2];
 bool __bootdata(boot_earlyprintk);
 size_t __bootdata(boot_rb_off);
+bool __bootdata(bootdebug);
 
 unsigned long __bootdata_preserved(VMALLOC_START);
 EXPORT_SYMBOL(VMALLOC_START);
@@ -882,13 +883,18 @@ static void __init log_component_list(void)
 }
 
 /*
- * Print avoiding interpretation of % in buf
+ * Print avoiding interpretation of % in buf and taking bootdebug option
+ * into consideration.
  */
 static void __init print_rb_entry(char *buf)
 {
 	char fmt[] = KERN_SOH "0boot: %s";
+	int level = printk_get_level(buf);
 
-	fmt[1] = printk_get_level(buf);
+	if (level == KERN_DEBUG[1] && !bootdebug)
+		return;
+
+	fmt[1] = level;
 	printk(fmt, printk_skip_level(buf));
 }