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iio: adc: xilinx-xadc: Push interrupts into hardirq context

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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: Xander Huff <xander.huff@ni.com>
Acked-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
This commit is contained in:
Xander Huff 2015-08-11 18:00:49 -05:00 committed by Jonathan Cameron
parent 70b2737e0a
commit 70581e0ef8
2 changed files with 10 additions and 29 deletions
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37
drivers/iio/adc/xilinx-xadc-core.c
View file

@ -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;

2
drivers/iio/adc/xilinx-xadc.h
View file

@ -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;
};