linux-kernel - [PATCH] comedi: 8255: Fail to attach if fail to request I/O port region

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Message-ID: <20251028112833.15033-1-abbotti@mev.co.uk>
Date: Tue, 28 Oct 2025 11:28:33 +0000
From: Ian Abbott <abbotti@....co.uk>
To: linux-kernel@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ian Abbott <abbotti@....co.uk>,
	H Hartley Sweeten <hsweeten@...ionengravers.com>
Subject: [PATCH] comedi: 8255: Fail to attach if fail to request I/O port region

The COMEDI standalone 8255 driver can be used to configure a COMEDI
device consisting of one of more subdevices, each using an 8255 digital
I/O chip mapped to a range of port I/O addresses.  The base port I/O
address of each chip is specified in an array of integer option values
by the `COMEDI_DEVCONFIG` ioctl.

When support for multiple 8255 subdevices per device was added in the
out-of-tree comedi 0.7.27 back in 1999, if any port I/O region could not
be requested, then the corresponding subdevice was set to be an "unused"
subdevice, and the COMEDI device would still be set-up OK as long as
those were the only types of errors.  That has persisted until the
present day, but seems a bit odd in retrospect.  All the other COMEDI
drivers that use port I/O or memory regions will fail to set up the
device if any region cannot be requested.  It seems unlikely that the
sys admin would deliberately choose a port that cannot be requested just
to leave a gap in the device's usable subdevice numbers, and failing to
set-up the device will provide a more noticeable indication that
something hasn't been set-up correctly, so change the driver to fail to
set up the device if any of the port I/O regions cannot be requested.

Signed-off-by: Ian Abbott <abbotti@....co.uk>
---
 drivers/comedi/drivers/8255.c | 20 +++++++++-----------
 1 file changed, 9 insertions(+), 11 deletions(-)

diff --git a/drivers/comedi/drivers/8255.c b/drivers/comedi/drivers/8255.c
index f45f7bd1c61a..5f70938b4477 100644
--- a/drivers/comedi/drivers/8255.c
+++ b/drivers/comedi/drivers/8255.c
@@ -77,19 +77,17 @@ static int dev_8255_attach(struct comedi_device *dev,
 		 * base address of the chip.
 		 */
 		ret = __comedi_request_region(dev, iobase, I8255_SIZE);
+		if (ret)
+			return ret;
+		ret = subdev_8255_io_init(dev, s, iobase);
 		if (ret) {
+			/*
+			 * Release the I/O port region here, as the
+			 * "detach" handler cannot find it.
+			 */
+			release_region(iobase, I8255_SIZE);
 			s->type = COMEDI_SUBD_UNUSED;
-		} else {
-			ret = subdev_8255_io_init(dev, s, iobase);
-			if (ret) {
-				/*
-				 * Release the I/O port region here, as the
-				 * "detach" handler cannot find it.
-				 */
-				release_region(iobase, I8255_SIZE);
-				s->type = COMEDI_SUBD_UNUSED;
-				return ret;
-			}
+			return ret;
 		}
 	}

-- 
2.51.0