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Message-Id: <1439334049-28671-1-git-send-email-xander.huff@ni.com>
Date: Tue, 11 Aug 2015 18:00:49 -0500
From: Xander Huff <xander.huff@...com>
To: jic23@...nel.org, bigeasy@...utronix.de, lars@...afoo.de
Cc: knaack.h@....de, pmeerw@...erw.net, michal.simek@...inx.com,
soren.brinkmann@...inx.com, linux-iio@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org,
linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org,
joe.hershberger@...com, joshc@...com, nathan.sullivan@...com,
jaeden.amero@...com, Xander Huff <xander.huff@...com>
Subject: [PATCH v4] 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
# /dev/cpu_dma_latency set to 0us
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
# /dev/cpu_dma_latency set to 0us
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@...com>
---
drivers/iio/adc/xilinx-xadc-core.c | 37 ++++++++++---------------------------
drivers/iio/adc/xilinx-xadc.h | 2 --
2 files changed, 10 insertions(+), 29 deletions(-)
diff --git a/drivers/iio/adc/xilinx-xadc-core.c b/drivers/iio/adc/xilinx-xadc-core.c
index ce93bd8..0370624 100644
--- a/drivers/iio/adc/xilinx-xadc-core.c
+++ b/drivers/iio/adc/xilinx-xadc-core.c
@@ -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;
diff --git a/drivers/iio/adc/xilinx-xadc.h b/drivers/iio/adc/xilinx-xadc.h
index 54adc50..f6f0819 100644
--- a/drivers/iio/adc/xilinx-xadc.h
+++ b/drivers/iio/adc/xilinx-xadc.h
@@ -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;
};
--
1.9.1
--
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