[PATCH v2] printk: Document that CONFIG_BOOT_PRINTK_DELAY required for boot_delay=

[Bjorn Helgaas <helgaas@kernel.org>]

From: Bjorn Helgaas <bhelgaas@google.com>

Document the fact that CONFIG_BOOT_PRINTK_DELAY must be enabled for the
"boot_delay" kernel parameter to work.  Also mention that "lpj=" may be
necessary.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
---
Changes from v1 (https://lore.kernel.org/all/20230123180440.901793-1-helgaas@kernel.org/):
- Clarify use of "lpj=".  Reword consequences of delay larger than 10000.

 Documentation/admin-guide/kernel-parameters.txt | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 6cfa6e3996cf..814e58487239 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -480,8 +480,10 @@
 			See Documentation/block/cmdline-partition.rst
 
 	boot_delay=	Milliseconds to delay each printk during boot.
-			Values larger than 10 seconds (10000) are changed to
-			no delay (0).
+			Only works if CONFIG_BOOT_PRINTK_DELAY is enabled,
+			and you may also have to specify "lpj=".  Boot_delay
+			values larger than 10 seconds (10000) are assumed
+			erroneous and ignored.
 			Format: integer
 
 	bootconfig	[KNL]
-- 
2.25.1