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Commit 98333021 authored by H Hartley Sweeten's avatar H Hartley Sweeten Committed by Greg Kroah-Hartman
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staging: comedi: das1800: document the spinlock 



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: default avatarH Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: default avatarIan Abbott <abbotti@mev.co.uk>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent fb90ec01

drivers/staging/comedi/drivers/das1800.c

+14 −4
Original line number Diff line number Diff line
@@ -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);

		}