[PATCH v2] Fix IRQ issue by setting IRQ_DISABLE_UNLAZY flag

[Masahiro Honda]

The Sigma-Delta ADCs supported by this driver can use SDO as an interrupt
line to indicate the completion of a conversion. However, some devices
cannot properly detect the completion of a conversion by an interrupt.
This is for the reason mentioned in the following commit.

commit e9849777d0e2 ("genirq: Add flag to force mask in
                      disable_irq[_nosync]()")

A read operation is performed by an extra interrupt before the complete
conversion. This patch provides an option to fix the issue by setting
IRQ_DISABLE_UNLAZY flag.

Signed-off-by: Masahiro Honda <honda@xxxxxxxxxxxxx>
---
v2:
 - Rework commit message.
 - Add a new entry in the Kconfig.
 - Call irq_clear_status_flags(irq, IRQ_DISABLE_UNLAZY) when freeing the IRQ.
v1: https://lore.kernel.org/linux-iio/20230306044737.862-1-honda@xxxxxxxxxxxxx/

 drivers/iio/adc/Kconfig          | 14 ++++++++++++++
 drivers/iio/adc/ad_sigma_delta.c | 31 ++++++++++++++++++++++++++-----
 2 files changed, 40 insertions(+), 5 deletions(-)

diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
index 45af2302b..78ab6e2d8 100644
--- a/drivers/iio/adc/Kconfig
+++ b/drivers/iio/adc/Kconfig
@@ -21,6 +21,20 @@ config AD_SIGMA_DELTA
 	select IIO_BUFFER
 	select IIO_TRIGGERED_BUFFER
 
+if AD_SIGMA_DELTA
+
+config AD_SIGMA_DELTA_USE_LAZY_IRQ
+	bool "Use lazy IRQ for sigma-delta ADCs"
+	depends on AD_SIGMA_DELTA
+	default n
+	help
+	  Some interrupt controllers have data read problem with ADCs depends on
+	  AD_SIGMA_DELTA.
+	  Say yes here to avoid the problem at the cost of performance overhead.
+	  If unsure, say N (but it's safe to say "Y").
+
+endif # if AD_SIGMA_DELTA
+
 config AD4130
 	tristate "Analog Device AD4130 ADC Driver"
 	depends on SPI
diff --git a/drivers/iio/adc/ad_sigma_delta.c b/drivers/iio/adc/ad_sigma_delta.c
index d8570f620..b9eae1e80 100644
--- a/drivers/iio/adc/ad_sigma_delta.c
+++ b/drivers/iio/adc/ad_sigma_delta.c
@@ -565,6 +565,16 @@ int ad_sd_validate_trigger(struct iio_dev *indio_dev, struct iio_trigger *trig)
 }
 EXPORT_SYMBOL_NS_GPL(ad_sd_validate_trigger, IIO_AD_SIGMA_DELTA);
 
+static void ad_sd_free_irq(void *sd)
+{
+	struct ad_sigma_delta *sigma_delta = sd;
+
+#ifdef CONFIG_AD_SIGMA_DELTA_USE_LAZY_IRQ
+	irq_clear_status_flags(sigma_delta->spi->irq, IRQ_DISABLE_UNLAZY);
+#endif
+	free_irq(sigma_delta->spi->irq, sigma_delta);
+}
+
 static int devm_ad_sd_probe_trigger(struct device *dev, struct iio_dev *indio_dev)
 {
 	struct ad_sigma_delta *sigma_delta = iio_device_get_drvdata(indio_dev);
@@ -584,11 +594,22 @@ static int devm_ad_sd_probe_trigger(struct device *dev, struct iio_dev *indio_de
 	init_completion(&sigma_delta->completion);
 
 	sigma_delta->irq_dis = true;
-	ret = devm_request_irq(dev, sigma_delta->spi->irq,
-			       ad_sd_data_rdy_trig_poll,
-			       sigma_delta->info->irq_flags | IRQF_NO_AUTOEN,
-			       indio_dev->name,
-			       sigma_delta);
+#ifdef CONFIG_AD_SIGMA_DELTA_USE_LAZY_IRQ
+	irq_set_status_flags(sigma_delta->spi->irq, IRQ_DISABLE_UNLAZY);
+#endif
+	ret = request_irq(sigma_delta->spi->irq,
+			  ad_sd_data_rdy_trig_poll,
+			  sigma_delta->info->irq_flags | IRQF_NO_AUTOEN,
+			  indio_dev->name,
+			  sigma_delta);
+	if (ret) {
+#ifdef CONFIG_AD_SIGMA_DELTA_USE_LAZY_IRQ
+		irq_clear_status_flags(sigma_delta->spi->irq, IRQ_DISABLE_UNLAZY);
+#endif
+		return ret;
+	}
+
+	ret = devm_add_action_or_reset(dev, ad_sd_free_irq, sigma_delta);
 	if (ret)
 		return ret;
 
-- 
2.34.1