The comedi_device spinlock is used to protect the indirect addressing
selected by the DAS1800_SELECT register. It also prevents races between
the interrupt handler and the analog input (*poll).
Update the comments to make this clear.
Signed-off-by: H Hartley Sweeten <hsweeten@xxxxxxxxxxxxxxxxxxx>
Cc: Ian Abbott <abbotti@xxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/staging/comedi/drivers/das1800.c | 18 ++++++++++++++----
1 file changed, 14 insertions(+), 4 deletions(-)
diff --git a/drivers/staging/comedi/drivers/das1800.c b/drivers/staging/comedi/drivers/das1800.c
index 8dae3845..a2108d3 100644
--- a/drivers/staging/comedi/drivers/das1800.c
+++ b/drivers/staging/comedi/drivers/das1800.c
@@ -517,8 +517,9 @@ static void das1800_ai_handler(struct comedi_device *dev)
struct comedi_cmd *cmd = &async->cmd;
unsigned int status = inb(dev->iobase + DAS1800_STATUS);
- /* select adc for base address + 0 */
+ /* select adc register (spinlock is already held) */
outb(ADC, dev->iobase + DAS1800_SELECT);
+
/* dma buffer full */
if (devpriv->irq_dma_bits & DMA_ENABLED) {
/* look for data from dma transfer even if dma terminal count hasn't happened yet */
@@ -562,9 +563,14 @@ static int das1800_ai_poll(struct comedi_device *dev,
{
unsigned long flags;
- /* prevent race with interrupt handler */
+ /*
+ * Protects the indirect addressing selected by DAS1800_SELECT
+ * in das1800_ai_handler() also prevents race with das1800_interrupt().
+ */
spin_lock_irqsave(&dev->spinlock, flags);
+
das1800_ai_handler(dev);
+
spin_unlock_irqrestore(&dev->spinlock, flags);
return comedi_buf_n_bytes_ready(s);
@@ -580,9 +586,12 @@ static irqreturn_t das1800_interrupt(int irq, void *d)
return IRQ_HANDLED;
}
- /* Prevent race with das1800_ai_poll() on multi processor systems.
- * Also protects indirect addressing in das1800_ai_handler */
+ /*
+ * Protects the indirect addressing selected by DAS1800_SELECT
+ * in das1800_ai_handler() also prevents race with das1800_ai_poll().
+ */
spin_lock(&dev->spinlock);
+
status = inb(dev->iobase + DAS1800_STATUS);
/* if interrupt was not caused by das-1800 */
@@ -1298,6 +1307,7 @@ static int das1800_attach(struct comedi_device *dev,
/* initialize all channels to 0V */
for (i = 0; i < s->n_chan; i++) {
+ /* spinlock is not necessary during the attach */
outb(DAC(i), dev->iobase + DAS1800_SELECT);
outw(0, dev->iobase + DAS1800_DAC);
}
--
2.6.3
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