[PATCH v2 2/2] Staging: comedi: comedi_fops: Fix "out of minor numbers for board device files"

[Cheah Kok Cheong]

If comedi module is loaded with the following max allowed parameter
[comedi_num_legacy_minors=48], subsequent loading of an auto-configured
device will fail at auto-configuration. If there's no fall back in
place then module loading will fail.

In this case, a default to auto-configure comedi_test module failed
to auto-configure with the following messages. It loaded but fell back
to unconfigured mode.

comedi_test comedi_testd: ran out of minor numbers for board device files
comedi_test comedi_testd: driver 'comedi_test' could not create device.
comedi_test: unable to auto-configure device

This is due to changes in commit 38b9722a4414
("staging: comedi: avoid releasing legacy minors automatically") which
will not allocate a minor number when comedi_num_legacy_minors equals
COMEDI_NUM_BOARD_MINORS. COMEDI_NUM_BOARD_MINORS is defined to be
0x30 which is 48.

This goes for a simple fix which limit comedi_num_legacy_minors to 47
instead of tinkering with comedi_alloc_board_minor() and
comedi_release_hardware_device().

Fix: commit 38b9722a4414 ("staging: comedi: avoid releasing legacy minors
automatically")

Signed-off-by: Cheah Kok Cheong <thrust73@xxxxxxxxx>
---

V2:
-Amend commit log to specify that comedi_test module failed
 to auto-configure and fell back to unconfigured mode.
 For other devices with no fall back, module loading will fail.

 drivers/staging/comedi/comedi_fops.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
index 354d264..339854f 100644
--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -2857,9 +2857,9 @@ static int __init comedi_init(void)
 
 	pr_info("version " COMEDI_RELEASE " - http://www.comedi.org\n";);
 
-	if (comedi_num_legacy_minors > COMEDI_NUM_BOARD_MINORS) {
+	if (comedi_num_legacy_minors >= COMEDI_NUM_BOARD_MINORS) {
 		pr_err("invalid value for module parameter \"comedi_num_legacy_minors\".  Valid values are 0 through %i.\n",
-		       COMEDI_NUM_BOARD_MINORS);
+		       COMEDI_NUM_BOARD_MINORS - 1);
 		return -EINVAL;
 	}
 
-- 
2.7.4