[RFC PATCH 1/8] iio: locking: introduce __cleanup() based direct mode claiming infrastructure

[Jonathan Cameron <jic23@kernel.org>]

From: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Allows use of:

	CLASS(iio_claim_direct, claimed_dev)(indio_dev);
	if (IS_ERR(claimed_dev))
		return PTR_ERR(claimed_dev);

	st = iio_priv(claimed_dev);

to automatically call iio_device_release_direct_mode() based on scope.
Typically seen in combination with local device specific locks which
are already have automated cleanup options via guard(mutex)(&st->lock)
and scoped_guard().  Using both together allows most error handling to
be automated.

Note that whilst this pattern results in a struct iio_dev *claimed_dev
that can be used, it is not necessary to do so as long as that pointer
has been checked for errors as in the example.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
---
 drivers/iio/industrialio-core.c |  4 ++++
 include/linux/iio/iio.h         | 25 +++++++++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
index c77745b594bd..93bfad105eb5 100644
--- a/drivers/iio/industrialio-core.c
+++ b/drivers/iio/industrialio-core.c
@@ -2065,6 +2065,10 @@ EXPORT_SYMBOL_GPL(iio_device_claim_direct_mode);
  */
 void iio_device_release_direct_mode(struct iio_dev *indio_dev)
 {
+	/* Auto cleanup can result in this being called with an ERR_PTR */
+	if (IS_ERR(indio_dev))
+		return;
+
 	mutex_unlock(&to_iio_dev_opaque(indio_dev)->mlock);
 }
 EXPORT_SYMBOL_GPL(iio_device_release_direct_mode);
diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h
index d0ce3b71106a..11c42170fda1 100644
--- a/include/linux/iio/iio.h
+++ b/include/linux/iio/iio.h
@@ -9,6 +9,7 @@
 
 #include <linux/device.h>
 #include <linux/cdev.h>
+#include <linux/cleanup.h>
 #include <linux/slab.h>
 #include <linux/iio/types.h>
 /* IIO TODO LIST */
@@ -644,6 +645,30 @@ int __devm_iio_device_register(struct device *dev, struct iio_dev *indio_dev,
 int iio_push_event(struct iio_dev *indio_dev, u64 ev_code, s64 timestamp);
 int iio_device_claim_direct_mode(struct iio_dev *indio_dev);
 void iio_device_release_direct_mode(struct iio_dev *indio_dev);
+/*
+ * Auto cleanup version of iio_device_claim_direct_mode,
+ *
+ *	CLASS(iio_claim_direct, claimed_dev)(indio_dev);
+ *	if (IS_ERR(claimed_dev))
+ *		return PTR_ERR(claimed_dev);
+ *
+ *	st = iio_priv(claimed_dev);
+ *	....
+ */
+DEFINE_CLASS(iio_claim_direct, struct iio_dev *,
+	     iio_device_release_direct_mode(_T),
+	     ({
+			struct iio_dev *dev;
+			int d = iio_device_claim_direct_mode(_T);
+
+			if (d < 0)
+				dev = ERR_PTR(d);
+			else
+				dev = _T;
+			dev;
+	     }),
+	     struct iio_dev *_T);
+
 int iio_device_claim_buffer_mode(struct iio_dev *indio_dev);
 void iio_device_release_buffer_mode(struct iio_dev *indio_dev);
 
-- 
2.42.0