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staging: comedi: das1800: document the spinlock

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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@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
H Hartley Sweeten
2016-04-08 12:41:53 -07:00
committed by Greg Kroah-Hartman
parent fb90ec01bc
commit 983330210f
1 changed files with 14 additions and 4 deletions
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18
drivers/staging/comedi/drivers/das1800.c
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@@ -490,8 +490,9 @@ 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 */
@@ -535,9 +536,14 @@ 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);
@@ -553,9 +559,12 @@ 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 */
@@ -1289,6 +1298,7 @@ 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);
}