linux-kernel - [PATCH 38/46] comedi: pcl818: Add sanity checks for I/O base address

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Message-ID: <20260130170416.49994-39-abbotti@mev.co.uk>
Date: Fri, 30 Jan 2026 16:48:03 +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 38/46] comedi: pcl818: Add sanity checks for I/O base address

The "pcl818" driver uses an admin-supplied configuration option
(`it->options[0]`) to configure the I/O port base address of a board in
the PCL-818 series.  It currently allows any base address to be
configured but the hardware devices only support base addresses
(configured by on-board DIP switches) from 0 to 0x3F0 on 16-byte
boundaries.  If the board has a FIFO and jumper JP6 is in the "Enabled"
(default) position, then the base address needs to be on a 32-byte
boundary and the length of the I/O port region will be 32 (to allow
access to the FIFO registers) instead of 16.  The state of jumper JP6 is
unknown, so if the board has a FIFO device and is being configured on an
odd 16-byte boundary, assume that jumper JP6 is in the "Disabled"
position (to disallow access to the FIFO registers).

Add a sanity check to ensure the device is not configured at an
unsupported base address.

If the board has a FIFO and is configured on an odd 16-byte boundary,
log a reminder that JP6 needs to be in the "Disabled" position for
correct operation.  If the board has a FIFO and is configured on an even
16-byte boundary and the configuration option has been set to use the
FIFO (`it->options[2] == -1`), log a reminder that JP6 needs to be in
the "Enabled" position.

Signed-off-by: Ian Abbott <abbotti@....co.uk>
---
 drivers/comedi/drivers/pcl818.c | 27 ++++++++++++++++++++++++---
 1 file changed, 24 insertions(+), 3 deletions(-)

diff --git a/drivers/comedi/drivers/pcl818.c b/drivers/comedi/drivers/pcl818.c
index 06fe06396f23..aa775a024fc7 100644
--- a/drivers/comedi/drivers/pcl818.c
+++ b/drivers/comedi/drivers/pcl818.c
@@ -981,6 +981,10 @@ static int pcl818_attach(struct comedi_device *dev, struct comedi_devconfig *it)
 	const struct pcl818_board *board = dev->board_ptr;
 	struct pcl818_private *devpriv;
 	struct comedi_subdevice *s;
+	unsigned int io_base = it->options[0];
+	bool fifo_is_supported = board->has_fifo && !(io_base & 0x10);
+	bool fifo_is_wanted = board->has_fifo && it->options[2] == -1;
+	unsigned int io_len = fifo_is_supported ? 0x20 : 0x10;
 	unsigned int osc_base;
 	int ret;

@@ -988,11 +992,28 @@ static int pcl818_attach(struct comedi_device *dev, struct comedi_devconfig *it)
 	if (!devpriv)
 		return -ENOMEM;

-	ret = comedi_request_region(dev, it->options[0],
-				    board->has_fifo ? 0x20 : 0x10);
+	ret = comedi_check_request_region(dev, io_base, io_len,
+					  0, 0x3ff, io_len);
 	if (ret)
 		return ret;

+	if (board->has_fifo) {
+		/* let user know about any required JP6 setting */
+		if (fifo_is_supported) {
+			if (fifo_is_wanted) {
+				dev_info(dev->class_dev,
+					 "Assuming JP6 is in \"Enabled\" (default) position to use the FIFO.\n");
+			}
+		} else {
+			dev_info(dev->class_dev,
+				 "JP6 needs to be in \"Disabled\" position for correct operation at this base address\n");
+			if (fifo_is_wanted) {
+				dev_warn(dev->class_dev,
+					 "FIFO cannot be used at this base address\n");
+			}
+		}
+	}
+
 	/* we can use IRQ 2-7 for async command support */
 	if (it->options[1] >= 2 && it->options[1] <= 7) {
 		ret = request_irq(it->options[1], pcl818_interrupt, 0,
@@ -1002,7 +1023,7 @@ static int pcl818_attach(struct comedi_device *dev, struct comedi_devconfig *it)
 	}

 	/* should we use the FIFO? */
-	if (dev->irq && board->has_fifo && it->options[2] == -1)
+	if (dev->irq && fifo_is_supported && fifo_is_wanted)
 		devpriv->usefifo = 1;

 	/* we need an IRQ to do DMA on channel 3 or 1 */
-- 
2.51.0