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Commit 70581e0e authored by Xander Huff's avatar Xander Huff Committed by Jonathan Cameron
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iio: adc: xilinx-xadc: Push interrupts into hardirq context 



The driver currently registers a pair of irq handlers using
request_threaded_irq(), however the synchronization mechanism between the
hardirq and the threadedirq handler is a regular spinlock.

Unfortunately, this breaks PREEMPT_RT builds, where a spinlock can sleep,
and is thus not able to be acquired from a hardirq handler. This patch gets
rid of the threaded handler and pushes all interrupt handling into the
hardirq context, and uses request_irq().

To validate that this change has no impact on RT performance, here are
cyclictest values with no processes running:

$ sudo cyclictest -S -m -p 98
policy: fifo: loadavg: 0.00 0.01 0.05 1/174 2539
T: 0 ( 1405) P:98 I:1000 C:167010520 Min: 9 Act: 12 Avg: 12 Max: 75
T: 1 ( 1862) P:98 I:1500 C:111340339 Min: 9 Act: 12 Avg: 12 Max: 73

Then, all xadc raw handles were accessed in a continuous loop via
/sys/bus/iio/devices/iio:device0:

$ sudo cyclictest -S -m -p 98
policy: fifo: loadavg: 7.84 7.70 7.63 3/182 4260
T: 0 ( 2559) P:98 I:1000 C:241557018 Min: 11 Act: 18 Avg: 21 Max: 74
T: 1 ( 2560) P:98 I:1500 C:161038006 Min: 10 Act: 21 Avg: 20 Max: 73

Signed-off-by: default avatarXander Huff <xander.huff@ni.com>
Acked-by: default avatarLars-Peter Clausen <lars@metafoo.de>
Signed-off-by: default avatarJonathan Cameron <jic23@kernel.org>
parent 70b2737e

drivers/iio/adc/xilinx-xadc-core.c

+10 −27
Original line number Diff line number Diff line
@@ -273,33 +273,13 @@ static void xadc_zynq_unmask_worker(struct work_struct *work) 
		schedule_delayed_work(&xadc->zynq_unmask_work,

				msecs_to_jiffies(XADC_ZYNQ_UNMASK_TIMEOUT));

	}

}



static irqreturn_t xadc_zynq_threaded_interrupt_handler(int irq, void *devid)

{

	struct iio_dev *indio_dev = devid;

	struct xadc *xadc = iio_priv(indio_dev);

	unsigned int alarm;



	spin_lock_irq(&xadc->lock);

	alarm = xadc->zynq_alarm;

	xadc->zynq_alarm = 0;

	spin_unlock_irq(&xadc->lock);



	xadc_handle_events(indio_dev, xadc_zynq_transform_alarm(alarm));



	/* unmask the required interrupts in timer. */

	schedule_delayed_work(&xadc->zynq_unmask_work,

			msecs_to_jiffies(XADC_ZYNQ_UNMASK_TIMEOUT));



	return IRQ_HANDLED;

}



static irqreturn_t xadc_zynq_interrupt_handler(int irq, void *devid)

{

	struct iio_dev *indio_dev = devid;

	struct xadc *xadc = iio_priv(indio_dev);

	irqreturn_t ret = IRQ_HANDLED;

	uint32_t status;



	xadc_read_reg(xadc, XADC_ZYNQ_REG_INTSTS, &status);
@@ -321,18 +301,23 @@ static irqreturn_t xadc_zynq_interrupt_handler(int irq, void *devid) 


	status &= XADC_ZYNQ_INT_ALARM_MASK;

	if (status) {

		xadc->zynq_alarm |= status;

		xadc->zynq_masked_alarm |= status;

		/*

		 * mask the current event interrupt,

		 * unmask it when the interrupt is no more active.

		 */

		xadc_zynq_update_intmsk(xadc, 0, 0);

		ret = IRQ_WAKE_THREAD;



		xadc_handle_events(indio_dev,

				xadc_zynq_transform_alarm(status));



		/* unmask the required interrupts in timer. */

		schedule_delayed_work(&xadc->zynq_unmask_work,

				msecs_to_jiffies(XADC_ZYNQ_UNMASK_TIMEOUT));

	}

	spin_unlock(&xadc->lock);



	return ret;

	return IRQ_HANDLED;

}



#define XADC_ZYNQ_TCK_RATE_MAX 50000000
@@ -437,7 +422,6 @@ static const struct xadc_ops xadc_zynq_ops = { 
	.setup = xadc_zynq_setup,

	.get_dclk_rate = xadc_zynq_get_dclk_rate,

	.interrupt_handler = xadc_zynq_interrupt_handler,

	.threaded_interrupt_handler = xadc_zynq_threaded_interrupt_handler,

	.update_alarm = xadc_zynq_update_alarm,

};
@@ -1225,9 +1209,8 @@ static int xadc_probe(struct platform_device *pdev) 
	if (ret)

		goto err_free_samplerate_trigger;



	ret = request_threaded_irq(irq, xadc->ops->interrupt_handler,

				xadc->ops->threaded_interrupt_handler,

				0, dev_name(&pdev->dev), indio_dev);

	ret = request_irq(irq, xadc->ops->interrupt_handler, 0,

			dev_name(&pdev->dev), indio_dev);

	if (ret)

		goto err_clk_disable_unprepare;

drivers/iio/adc/xilinx-xadc.h

+0 −2
Original line number Diff line number Diff line
@@ -60,7 +60,6 @@ struct xadc { 


	enum xadc_external_mux_mode external_mux_mode;



	unsigned int zynq_alarm;

	unsigned int zynq_masked_alarm;

	unsigned int zynq_intmask;

	struct delayed_work zynq_unmask_work;
@@ -79,7 +78,6 @@ struct xadc_ops { 
	void (*update_alarm)(struct xadc *, unsigned int);

	unsigned long (*get_dclk_rate)(struct xadc *);

	irqreturn_t (*interrupt_handler)(int, void *);

	irqreturn_t (*threaded_interrupt_handler)(int, void *);



	unsigned int flags;

};