[PATCH RFC 2/4] printk: deprecate boot_delay in favour of printk_delay

[Andrew Murray]

The boot_delay (BOOT_PRINTK_DELAY) kernel parameter and printk_delay sysctl
are two distinct mechanisms for providing similar functionality which add a
delay prior to each printed printk message.

boot_delay provides a kernel parameter for delaying printk output from
kernel start through to boot (SYSTEM_RUNNING), whereas printk_delay is
configurable only via sysctl and thus is only used post boot.

Let's deprecate the boot_delay feature in favour of printk_delay. In order
to preserve functionality, we'll also extend printk_delay such that it can
additionally configured via a kernel parameter.

Signed-off-by: Andrew Murray <amurray@xxxxxxxxxxxxxxxxxxxx>
---
 kernel/printk/printk.c | 75 ++++++++++++++++++++++++++++++++------------------
 1 file changed, 48 insertions(+), 27 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 822fcdff7b21ac00cfa655c3d9b4de2698fcb7d8..ca510b9c76458f5c1e059200060d9d6be4c859b3 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1291,40 +1291,28 @@ static bool suppress_message_printing(int level)
 
 #ifdef CONFIG_GENERIC_CALIBRATE_DELAY
 
-static int boot_delay; /* msecs delay after each printk during bootup */
 static unsigned long long loops_per_msec;	/* based on boot_delay */
 
-static int __init boot_delay_setup(char *str)
+static void __init printk_delay_calculate(void)
 {
 	unsigned long lpj;
 
 	lpj = preset_lpj ? preset_lpj : 1000000;	/* some guess */
 	loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
 
-	get_option(&str, &boot_delay);
-	if (boot_delay > 10 * 1000)
-		boot_delay = 0;
-
-	pr_debug("boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
+	pr_debug("printk_delay: %u, preset_lpj: %ld, lpj: %lu, "
 		"HZ: %d, loops_per_msec: %llu\n",
-		boot_delay, preset_lpj, lpj, HZ, loops_per_msec);
-	return 0;
+		printk_delay_msec, preset_lpj, lpj, HZ, loops_per_msec);
 }
-early_param("boot_delay", boot_delay_setup);
 
-static void boot_delay_msec(int level)
+static void early_boot_delay_msec(void)
 {
 	unsigned long long k;
 	unsigned long timeout;
-	bool suppress = !is_printk_force_console() &&
-			suppress_message_printing(level);
-
-	if ((boot_delay == 0 || system_state >= SYSTEM_RUNNING) || suppress)
-		return;
 
-	k = (unsigned long long)loops_per_msec * boot_delay;
+	k = (unsigned long long)loops_per_msec * printk_delay_msec;
 
-	timeout = jiffies + msecs_to_jiffies(boot_delay);
+	timeout = jiffies + msecs_to_jiffies(printk_delay_msec);
 	while (k) {
 		k--;
 		cpu_relax();
@@ -1339,11 +1327,34 @@ static void boot_delay_msec(int level)
 	}
 }
 #else
-static inline void boot_delay_msec(int level)
+static inline void __init printk_delay_calculate(void)
+{
+}
+
+static inline void early_boot_delay_msec(void)
 {
 }
 #endif
 
+static int __init printk_delay_setup(char *str)
+{
+	get_option(&str, &printk_delay_msec);
+	if (printk_delay_msec > 10 * 1000)
+		printk_delay_msec = 0;
+
+	printk_delay_calculate();
+
+	return 0;
+}
+early_param("printk_delay", printk_delay_setup);
+
+static int __init boot_delay_setup(char *str)
+{
+	pr_warn("boot_delay will soon be deprecated, please use printk_delay instead");
+	return printk_delay_setup(str);
+}
+early_param("boot_delay", boot_delay_setup);
+
 static bool printk_time = IS_ENABLED(CONFIG_PRINTK_TIME);
 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
 
@@ -2119,18 +2130,28 @@ static u8 *__printk_recursion_counter(void)
 
 int printk_delay_msec __read_mostly;
 
+static inline void late_boot_delay_msec(void)
+{
+	int m = printk_delay_msec;
+
+	while (m--) {
+		mdelay(1);
+		touch_nmi_watchdog();
+	}
+}
+
 static inline void printk_delay(int level)
 {
-	boot_delay_msec(level);
+	bool suppress = !is_printk_force_console() &&
+			suppress_message_printing(level);
 
-	if (unlikely(printk_delay_msec)) {
-		int m = printk_delay_msec;
+	if (likely(!printk_delay_msec) || suppress)
+		return;
 
-		while (m--) {
-			mdelay(1);
-			touch_nmi_watchdog();
-		}
-	}
+	if (system_state < SYSTEM_RUNNING)
+		early_boot_delay_msec();
+	else
+		late_boot_delay_msec();
 }
 
 #define CALLER_ID_MASK 0x80000000

-- 
2.34.1