[PATCH 6.18 051/227] comedi: dmm32at: serialize use of paged registers

Greg Kroah-Hartman
2026-01-28T15:53:01Z

From: Ian Abbott <abbotti@mev.co.uk>

commit e03b29b55f2b7c345a919a6ee36633b06bf3fb56 upstream.

Some of the hardware registers of the DMM-32-AT board are multiplexed,
using the least significant two bits of the Miscellaneous Control
register to select the function of registers at offsets 12 to 15:

00 => 8254 timer/counter registers are accessible
01 => 8255 digital I/O registers are accessible
10 => Reserved
11 => Calibration registers are accessible

The interrupt service routine (`dmm32at_isr()`) clobbers the bottom two
bits of the register with value 00, which would interfere with access to
the 8255 registers by the `dm32at_8255_io()` function (used for Comedi
instruction handling on the digital I/O subdevice).

Make use of the generic Comedi device spin-lock `dev->spinlock` (which
is otherwise unused by this driver) to serialize access to the
miscellaneous control register and paged registers.

Fixes: 3c501880ac44 ("Staging: comedi: add dmm32at driver")
Cc: stable@vger.kernel.org
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Link: https://patch.msgid.link/20260112162835.91688-1-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/comedi/drivers/dmm32at.c | 32 ++++++++++++++++++++++++++++++--
1 file changed, 30 insertions(+), 2 deletions(-)

--- a/drivers/comedi/drivers/dmm32at.c
+++ b/drivers/comedi/drivers/dmm32at.c
@@ -330,6 +330,7 @@ static int dmm32at_ai_cmdtest(struct com

static void dmm32at_setaitimer(struct comedi_device *dev, unsigned int nansec)
{
+ unsigned long irq_flags;
unsigned char lo1, lo2, hi2;
unsigned short both2;

@@ -342,6 +343,9 @@ static void dmm32at_setaitimer(struct co
/* set counter clocks to 10MHz, disable all aux dio */
outb(0, dev->iobase + DMM32AT_CTRDIO_CFG_REG);

+ /* serialize access to control register and paged registers */
+ spin_lock_irqsave(&dev->spinlock, irq_flags);
+
/* get access to the clock regs */
outb(DMM32AT_CTRL_PAGE_8254, dev->iobase + DMM32AT_CTRL_REG);

@@ -354,6 +358,8 @@ static void dmm32at_setaitimer(struct co
outb(lo2, dev->iobase + DMM32AT_CLK2);
outb(hi2, dev->iobase + DMM32AT_CLK2);

+ spin_unlock_irqrestore(&dev->spinlock, irq_flags);
+
/* enable the ai conversion interrupt and the clock to start scans */
outb(DMM32AT_INTCLK_ADINT |
DMM32AT_INTCLK_CLKEN | DMM32AT_INTCLK_CLKSEL,
@@ -363,13 +369,19 @@ static void dmm32at_setaitimer(struct co
static int dmm32at_ai_cmd(struct comedi_device *dev, struct comedi_subdevice *s)
{
struct comedi_cmd *cmd = &s->async->cmd;
+ unsigned long irq_flags;
int ret;

dmm32at_ai_set_chanspec(dev, s, cmd->chanlist[0], cmd->chanlist_len);

+ /* serialize access to control register and paged registers */
+ spin_lock_irqsave(&dev->spinlock, irq_flags);
+
/* reset the interrupt just in case */
outb(DMM32AT_CTRL_INTRST, dev->iobase + DMM32AT_CTRL_REG);

+ spin_unlock_irqrestore(&dev->spinlock, irq_flags);
+
/*
* wait for circuit to settle
* we don't have the 'insn' here but it's not needed
@@ -429,8 +441,13 @@ static irqreturn_t dmm32at_isr(int irq,
comedi_handle_events(dev, s);
}

+ /* serialize access to control register and paged registers */
+ spin_lock(&dev->spinlock);
+
/* reset the interrupt */
outb(DMM32AT_CTRL_INTRST, dev->iobase + DMM32AT_CTRL_REG);
+
+ spin_unlock(&dev->spinlock);
return IRQ_HANDLED;
}

@@ -481,14 +498,25 @@ static int dmm32at_ao_insn_write(struct
static int dmm32at_8255_io(struct comedi_device *dev,
int dir, int port, int data, unsigned long regbase)
{
+ unsigned long irq_flags;
+ int ret;
+
+ /* serialize access to control register and paged registers */
+ spin_lock_irqsave(&dev->spinlock, irq_flags);
+
/* get access to the DIO regs */
outb(DMM32AT_CTRL_PAGE_8255, dev->iobase + DMM32AT_CTRL_REG);

if (dir) {
outb(data, dev->iobase + regbase + port);
- return 0;
+ ret = 0;
+ } else {
+ ret = inb(dev->iobase + regbase + port);
}
- return inb(dev->iobase + regbase + port);
+
+ spin_unlock_irqrestore(&dev->spinlock, irq_flags);
+
+ return ret;
}

/* Make sure the board is there and put it to a known state */