[PATCH v10 0/7] iio: add new backend framework

[PATCH v10 0/7] iio: add new backend framework

[Nuno Sa]

v1:
 https://lore.kernel.org/linux-iio/20231204144925.4fe9922f@jic23-huawei/T/#m222f5175273b81dbfe40b7f0daffcdc67d6cb8ff

v2:
 https://lore.kernel.org/r/20231208-dev-iio-backend-v2-0-5450951895e1@analog.com

v3:
 https://lore.kernel.org/linux-iio/20231213-dev-iio-backend-v3-0-bb9f12a5c6dc@analog.com/

v4:
 https://lore.kernel.org/r/20231220-iio-backend-v4-0-998e9148b692@analog.com

v5:
 https://lore.kernel.org/r/20240112-iio-backend-v5-0-bdecad041ab4@analog.com

v6:
 https://lore.kernel.org/r/20240119-iio-backend-v6-0-189536c35a05@analog.com

v7
 https://lore.kernel.org/r/20240123-iio-backend-v7-0-1bff236b8693@analog.com

v8:
 https://lore.kernel.org/r/20240202-iio-backend-v8-0-f65ee8c8203d@analog.com

v9:
 https://lore.kernel.org/r/20240206-iio-backend-v9-0-df66d159c000@analog.com

Changes in v10:
 - Patch 5
   * Removed meaningless @ in function names;
   * Added ascii diagram for the typicaly HW setup (Andy request);
   * Add missing period;
   * Use of dev_err_probe() in APIs meant to be called during probe(). 
 - Patch 6
   * Removed unneeded blank line;
   * Fixed some English in the commit message.

Jonathan, the series is based on next-20240207 since it already includes
the io-channels fix Rob applied in his tree. I guess it should land in rc3 so
after you rebase, all patches should apply cleanly (if applying them of course
:)). Let me know if anything fails...

Keeping the block diagram  so we don't have to follow links
to check one of the typical setups.

                                           -------------------------------------------------------
 ------------------                        | -----------         ------------      -------  FPGA |
 |     ADC        |------------------------| | AXI ADC |---------| DMA CORE |------| RAM |       |
 | (Frontend/IIO) | Serial Data (eg: LVDS) | |(backend)|---------|          |------|     |       |
 |                |------------------------| -----------         ------------      -------       |
 ------------------                        -------------------------------------------------------

---
Nuno Sa (6):
      dt-bindings: adc: ad9467: add new io-backend property
      dt-bindings: adc: axi-adc: update bindings for backend framework
      iio: buffer-dmaengine: export buffer alloc and free functions
      iio: add the IIO backend framework
      iio: adc: ad9467: convert to backend framework
      iio: adc: adi-axi-adc: move to backend framework

Olivier Moysan (1):
      of: property: add device link support for io-backends

 .../devicetree/bindings/iio/adc/adi,ad9467.yaml    |   4 +
 .../devicetree/bindings/iio/adc/adi,axi-adc.yaml   |   8 +-
 MAINTAINERS                                        |   8 +
 drivers/iio/Kconfig                                |   9 +
 drivers/iio/Makefile                               |   1 +
 drivers/iio/adc/Kconfig                            |   4 +-
 drivers/iio/adc/ad9467.c                           | 267 ++++++++-----
 drivers/iio/adc/adi-axi-adc.c                      | 379 +++++--------------
 drivers/iio/buffer/industrialio-buffer-dmaengine.c |   8 +-
 drivers/iio/industrialio-backend.c                 | 418 +++++++++++++++++++++
 drivers/of/property.c                              |   2 +
 include/linux/iio/adc/adi-axi-adc.h                |  68 ----
 include/linux/iio/backend.h                        |  72 ++++
 include/linux/iio/buffer-dmaengine.h               |   3 +
 14 files changed, 798 insertions(+), 453 deletions(-)
---
base-commit: 2ae0a045e6814c8c1d676d6153c605a65746aa29
change-id: 20231219-iio-backend-a3dc1a6a7a58
--

Thanks!
- Nuno Sá

[PATCH v10 1/7] dt-bindings: adc: ad9467: add new io-backend property

[Nuno Sa]

The ad9467 will make use of the new IIO backend framework which is a
provider - consumer interface where IIO backends provide services to
consumers. As such, and being this device a consumer,  add the new
generic io-backend property to the bindings.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Nuno Sa <nuno.sa@analog.com>
---
 Documentation/devicetree/bindings/iio/adc/adi,ad9467.yaml | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Documentation/devicetree/bindings/iio/adc/adi,ad9467.yaml b/Documentation/devicetree/bindings/iio/adc/adi,ad9467.yaml
index 7aa748d6b7a0..eecd5fbab695 100644
--- a/Documentation/devicetree/bindings/iio/adc/adi,ad9467.yaml
+++ b/Documentation/devicetree/bindings/iio/adc/adi,ad9467.yaml
@@ -44,6 +44,9 @@ properties:
       Pin that controls the powerdown mode of the device.
     maxItems: 1
 
+  io-backends:
+    maxItems: 1
+
   reset-gpios:
     description:
       Reset pin for the device.
@@ -68,6 +71,7 @@ examples:
             reg = <0>;
             clocks = <&adc_clk>;
             clock-names = "adc-clk";
+            io-backends = <&iio_backend>;
         };
     };
 ...

-- 
2.43.0

[PATCH v10 2/7] dt-bindings: adc: axi-adc: update bindings for backend framework

[Nuno Sa]

'adi,adc-dev' is now deprecated and must not be used anymore. Hence,
also remove it from being required.

The reason why it's being deprecated is because the axi-adc CORE is now
an IIO service provider hardware (IIO backends) for consumers to make use
of. Before, the logic with 'adi,adc-dev' was the opposite (it was kind
of consumer referencing other nodes/devices) and that proved to be wrong
and to not scale.

Now, IIO consumers of this hardware are expected to reference it using the
io-backends property. Hence, the new '#io-backend-cells' is being added
so the device is easily identified as a provider.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Nuno Sa <nuno.sa@analog.com>
---
 Documentation/devicetree/bindings/iio/adc/adi,axi-adc.yaml | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/Documentation/devicetree/bindings/iio/adc/adi,axi-adc.yaml b/Documentation/devicetree/bindings/iio/adc/adi,axi-adc.yaml
index 9996dd93f84b..3d49d21ad33d 100644
--- a/Documentation/devicetree/bindings/iio/adc/adi,axi-adc.yaml
+++ b/Documentation/devicetree/bindings/iio/adc/adi,axi-adc.yaml
@@ -39,12 +39,15 @@ properties:
     $ref: /schemas/types.yaml#/definitions/phandle
     description:
       A reference to a the actual ADC to which this FPGA ADC interfaces to.
+    deprecated: true
+
+  '#io-backend-cells':
+    const: 0
 
 required:
   - compatible
   - dmas
   - reg
-  - adi,adc-dev
 
 additionalProperties: false
 
@@ -55,7 +58,6 @@ examples:
         reg = <0x44a00000 0x10000>;
         dmas = <&rx_dma 0>;
         dma-names = "rx";
-
-        adi,adc-dev = <&spi_adc>;
+        #io-backend-cells = <0>;
     };
 ...

-- 
2.43.0

[PATCH v10 3/7] of: property: add device link support for io-backends

[Nuno Sa]

From: Olivier Moysan <olivier.moysan@foss.st.com>

Add support for creating device links out of more DT properties.

Signed-off-by: Olivier Moysan <olivier.moysan@foss.st.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Nuno Sa <nuno.sa@analog.com>
---
 drivers/of/property.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/of/property.c b/drivers/of/property.c
index a7be85b0bfb6..4669fa2b2008 100644
--- a/drivers/of/property.c
+++ b/drivers/of/property.c
@@ -1251,6 +1251,7 @@ DEFINE_SIMPLE_PROP(interconnects, "interconnects", "#interconnect-cells")
 DEFINE_SIMPLE_PROP(iommus, "iommus", "#iommu-cells")
 DEFINE_SIMPLE_PROP(mboxes, "mboxes", "#mbox-cells")
 DEFINE_SIMPLE_PROP(io_channels, "io-channels", "#io-channel-cells")
+DEFINE_SIMPLE_PROP(io_backends, "io-backends", "#io-backend-cells")
 DEFINE_SIMPLE_PROP(interrupt_parent, "interrupt-parent", NULL)
 DEFINE_SIMPLE_PROP(dmas, "dmas", "#dma-cells")
 DEFINE_SIMPLE_PROP(power_domains, "power-domains", "#power-domain-cells")
@@ -1341,6 +1342,7 @@ static const struct supplier_bindings of_supplier_bindings[] = {
 	{ .parse_prop = parse_iommu_maps, .optional = true, },
 	{ .parse_prop = parse_mboxes, },
 	{ .parse_prop = parse_io_channels, },
+	{ .parse_prop = parse_io_backends, },
 	{ .parse_prop = parse_interrupt_parent, },
 	{ .parse_prop = parse_dmas, .optional = true, },
 	{ .parse_prop = parse_power_domains, },

-- 
2.43.0

[PATCH v10 4/7] iio: buffer-dmaengine: export buffer alloc and free functions

[Nuno Sa]

Export iio_dmaengine_buffer_free() and iio_dmaengine_buffer_alloc().
This is in preparation of introducing IIO backends support. This will
allow us to allocate a buffer and control it's lifetime from a device
different from the one holding the DMA firmware properties. Effectively,
in this case the struct device holding the firmware information about
the DMA channels is not the same as iio_dev->dev.parent (typical case).

While at it, namespace the buffer-dmaengine exports and update the
current user of these buffers.

Signed-off-by: Nuno Sa <nuno.sa@analog.com>
---
 drivers/iio/adc/adi-axi-adc.c                      | 1 +
 drivers/iio/buffer/industrialio-buffer-dmaengine.c | 8 +++++---
 include/linux/iio/buffer-dmaengine.h               | 3 +++
 3 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/iio/adc/adi-axi-adc.c b/drivers/iio/adc/adi-axi-adc.c
index c247ff1541d2..0f21d1d98b9f 100644
--- a/drivers/iio/adc/adi-axi-adc.c
+++ b/drivers/iio/adc/adi-axi-adc.c
@@ -447,3 +447,4 @@ module_platform_driver(adi_axi_adc_driver);
 MODULE_AUTHOR("Michael Hennerich <michael.hennerich@analog.com>");
 MODULE_DESCRIPTION("Analog Devices Generic AXI ADC IP core driver");
 MODULE_LICENSE("GPL v2");
+MODULE_IMPORT_NS(IIO_DMAENGINE_BUFFER);
diff --git a/drivers/iio/buffer/industrialio-buffer-dmaengine.c b/drivers/iio/buffer/industrialio-buffer-dmaengine.c
index 45fe7d0d42ee..a18c1da292af 100644
--- a/drivers/iio/buffer/industrialio-buffer-dmaengine.c
+++ b/drivers/iio/buffer/industrialio-buffer-dmaengine.c
@@ -159,7 +159,7 @@ static const struct iio_dev_attr *iio_dmaengine_buffer_attrs[] = {
  * Once done using the buffer iio_dmaengine_buffer_free() should be used to
  * release it.
  */
-static struct iio_buffer *iio_dmaengine_buffer_alloc(struct device *dev,
+struct iio_buffer *iio_dmaengine_buffer_alloc(struct device *dev,
 	const char *channel)
 {
 	struct dmaengine_buffer *dmaengine_buffer;
@@ -210,6 +210,7 @@ static struct iio_buffer *iio_dmaengine_buffer_alloc(struct device *dev,
 	kfree(dmaengine_buffer);
 	return ERR_PTR(ret);
 }
+EXPORT_SYMBOL_NS_GPL(iio_dmaengine_buffer_alloc, IIO_DMAENGINE_BUFFER);
 
 /**
  * iio_dmaengine_buffer_free() - Free dmaengine buffer
@@ -217,7 +218,7 @@ static struct iio_buffer *iio_dmaengine_buffer_alloc(struct device *dev,
  *
  * Frees a buffer previously allocated with iio_dmaengine_buffer_alloc().
  */
-static void iio_dmaengine_buffer_free(struct iio_buffer *buffer)
+void iio_dmaengine_buffer_free(struct iio_buffer *buffer)
 {
 	struct dmaengine_buffer *dmaengine_buffer =
 		iio_buffer_to_dmaengine_buffer(buffer);
@@ -227,6 +228,7 @@ static void iio_dmaengine_buffer_free(struct iio_buffer *buffer)
 
 	iio_buffer_put(buffer);
 }
+EXPORT_SYMBOL_NS_GPL(iio_dmaengine_buffer_free, IIO_DMAENGINE_BUFFER);
 
 static void __devm_iio_dmaengine_buffer_free(void *buffer)
 {
@@ -287,7 +289,7 @@ int devm_iio_dmaengine_buffer_setup(struct device *dev,
 
 	return iio_device_attach_buffer(indio_dev, buffer);
 }
-EXPORT_SYMBOL_GPL(devm_iio_dmaengine_buffer_setup);
+EXPORT_SYMBOL_NS_GPL(devm_iio_dmaengine_buffer_setup, IIO_DMAENGINE_BUFFER);
 
 MODULE_AUTHOR("Lars-Peter Clausen <lars@metafoo.de>");
 MODULE_DESCRIPTION("DMA buffer for the IIO framework");
diff --git a/include/linux/iio/buffer-dmaengine.h b/include/linux/iio/buffer-dmaengine.h
index 5c355be89814..cbb8ba957fad 100644
--- a/include/linux/iio/buffer-dmaengine.h
+++ b/include/linux/iio/buffer-dmaengine.h
@@ -10,6 +10,9 @@
 struct iio_dev;
 struct device;
 
+struct iio_buffer *iio_dmaengine_buffer_alloc(struct device *dev,
+					      const char *channel);
+void iio_dmaengine_buffer_free(struct iio_buffer *buffer);
 int devm_iio_dmaengine_buffer_setup(struct device *dev,
 				    struct iio_dev *indio_dev,
 				    const char *channel);

-- 
2.43.0

[PATCH v10 5/7] iio: add the IIO backend framework

[Nuno Sa]

This is a Framework to handle complex IIO aggregate devices.

The typical architecture is to have one device as the frontend device which
can be "linked" against one or multiple backend devices. All the IIO and
userspace interface is expected to be registers/managed by the frontend
device which will callback into the backends when needed (to get/set
some configuration that it does not directly control).

The basic framework interface is pretty simple:
 - Backends should register themselves with @devm_iio_backend_register()
 - Frontend devices should get backends with @devm_iio_backend_get()

Signed-off-by: Nuno Sa <nuno.sa@analog.com>
---
 MAINTAINERS                        |   8 +
 drivers/iio/Kconfig                |   9 +
 drivers/iio/Makefile               |   1 +
 drivers/iio/industrialio-backend.c | 418 +++++++++++++++++++++++++++++++++++++
 include/linux/iio/backend.h        |  72 +++++++
 5 files changed, 508 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 87b61a53462b..98a9c56099f7 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -10417,6 +10417,14 @@ L:	linux-media@vger.kernel.org
 S:	Maintained
 F:	drivers/media/rc/iguanair.c
 
+IIO BACKEND FRAMEWORK
+M:	Nuno Sa <nuno.sa@analog.com>
+R:	Olivier Moysan <olivier.moysan@foss.st.com>
+L:	linux-iio@vger.kernel.org
+S:	Maintained
+F:	drivers/iio/industrialio-backend.c
+F:	include/linux/iio/backend.h
+
 IIO DIGITAL POTENTIOMETER DAC
 M:	Peter Rosin <peda@axentia.se>
 L:	linux-iio@vger.kernel.org
diff --git a/drivers/iio/Kconfig b/drivers/iio/Kconfig
index 52eb46ef84c1..9c351ffc7bed 100644
--- a/drivers/iio/Kconfig
+++ b/drivers/iio/Kconfig
@@ -71,6 +71,15 @@ config IIO_TRIGGERED_EVENT
 	help
 	  Provides helper functions for setting up triggered events.
 
+config IIO_BACKEND
+	tristate
+	help
+	  Framework to handle complex IIO aggregate devices. The typical
+	  architecture that can make use of this framework is to have one
+	  device as the frontend device which can be "linked" against one or
+	  multiple backend devices. The framework then makes it easy to get
+	  and control such backend devices.
+
 source "drivers/iio/accel/Kconfig"
 source "drivers/iio/adc/Kconfig"
 source "drivers/iio/addac/Kconfig"
diff --git a/drivers/iio/Makefile b/drivers/iio/Makefile
index 9622347a1c1b..0ba0e1521ba4 100644
--- a/drivers/iio/Makefile
+++ b/drivers/iio/Makefile
@@ -13,6 +13,7 @@ obj-$(CONFIG_IIO_GTS_HELPER) += industrialio-gts-helper.o
 obj-$(CONFIG_IIO_SW_DEVICE) += industrialio-sw-device.o
 obj-$(CONFIG_IIO_SW_TRIGGER) += industrialio-sw-trigger.o
 obj-$(CONFIG_IIO_TRIGGERED_EVENT) += industrialio-triggered-event.o
+obj-$(CONFIG_IIO_BACKEND) += industrialio-backend.o
 
 obj-y += accel/
 obj-y += adc/
diff --git a/drivers/iio/industrialio-backend.c b/drivers/iio/industrialio-backend.c
new file mode 100644
index 000000000000..2fea2bbbe47f
--- /dev/null
+++ b/drivers/iio/industrialio-backend.c
@@ -0,0 +1,418 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Framework to handle complex IIO aggregate devices.
+ *
+ * The typical architecture is to have one device as the frontend device which
+ * can be "linked" against one or multiple backend devices. All the IIO and
+ * userspace interface is expected to be registers/managed by the frontend
+ * device which will callback into the backends when needed (to get/set some
+ * configuration that it does not directly control).
+ *
+ *                                           -------------------------------------------------------
+ * ------------------                        | ------------         ------------      -------  FPGA|
+ * |     ADC        |------------------------| | ADC CORE |---------| DMA CORE |------| RAM |      |
+ * | (Frontend/IIO) | Serial Data (eg: LVDS) | |(backend) |---------|          |------|     |      |
+ * |                |------------------------| ------------         ------------      -------      |
+ * ------------------                        -------------------------------------------------------
+ *
+ * The framework interface is pretty simple:
+ *   - Backends should register themselves with devm_iio_backend_register()
+ *   - Frontend devices should get backends with devm_iio_backend_get()
+ *
+ * Also to note that the primary target for this framework are converters like
+ * ADC/DACs so iio_backend_ops will have some operations typical of converter
+ * devices. On top of that, this is "generic" for all IIO which means any kind
+ * of device can make use of the framework. That said, If the iio_backend_ops
+ * struct begins to grow out of control, we can always refactor things so that
+ * the industrialio-backend.c is only left with the really generic stuff. Then,
+ * we can build on top of it depending on the needs.
+ *
+ * Copyright (C) 2023-2024 Analog Devices Inc.
+ */
+#define dev_fmt(fmt) "iio-backend: " fmt
+
+#include <linux/cleanup.h>
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/errno.h>
+#include <linux/list.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/property.h>
+#include <linux/slab.h>
+#include <linux/types.h>
+
+#include <linux/iio/backend.h>
+
+struct iio_backend {
+	struct list_head entry;
+	const struct iio_backend_ops *ops;
+	struct device *dev;
+	struct module *owner;
+	void *priv;
+};
+
+/*
+ * Helper struct for requesting buffers. This ensures that we have all data
+ * that we need to free the buffer in a device managed action.
+ */
+struct iio_backend_buffer_pair {
+	struct iio_backend *back;
+	struct iio_buffer *buffer;
+};
+
+static LIST_HEAD(iio_back_list);
+static DEFINE_MUTEX(iio_back_lock);
+
+/*
+ * Helper macros to call backend ops. Makes sure the option is supported.
+ */
+#define iio_backend_check_op(back, op) ({ \
+	struct iio_backend *____back = back;				\
+	int ____ret = 0;						\
+									\
+	if (!____back->ops->op)						\
+		____ret = -EOPNOTSUPP;					\
+									\
+	____ret;							\
+})
+
+#define iio_backend_op_call(back, op, args...) ({		\
+	struct iio_backend *__back = back;			\
+	int __ret;						\
+								\
+	__ret = iio_backend_check_op(__back, op);		\
+	if (!__ret)						\
+		__ret = __back->ops->op(__back, ##args);	\
+								\
+	__ret;							\
+})
+
+#define iio_backend_ptr_op_call(back, op, args...) ({		\
+	struct iio_backend *__back = back;			\
+	void *ptr_err;						\
+	int __ret;						\
+								\
+	__ret = iio_backend_check_op(__back, op);		\
+	if (__ret)						\
+		ptr_err = ERR_PTR(__ret);			\
+	else							\
+		ptr_err = __back->ops->op(__back, ##args);	\
+								\
+	ptr_err;						\
+})
+
+#define iio_backend_void_op_call(back, op, args...) {		\
+	struct iio_backend *__back = back;			\
+	int __ret;						\
+								\
+	__ret = iio_backend_check_op(__back, op);		\
+	if (!__ret)						\
+		__back->ops->op(__back, ##args);		\
+}
+
+/**
+ * iio_backend_chan_enable - Enable a backend channel
+ * @back:	Backend device
+ * @chan:	Channel number
+ *
+ * RETURNS:
+ * 0 on success, negative error number on failure.
+ */
+int iio_backend_chan_enable(struct iio_backend *back, unsigned int chan)
+{
+	return iio_backend_op_call(back, chan_enable, chan);
+}
+EXPORT_SYMBOL_NS_GPL(iio_backend_chan_enable, IIO_BACKEND);
+
+/**
+ * iio_backend_chan_disable - Disable a backend channel
+ * @back:	Backend device
+ * @chan:	Channel number
+ *
+ * RETURNS:
+ * 0 on success, negative error number on failure.
+ */
+int iio_backend_chan_disable(struct iio_backend *back, unsigned int chan)
+{
+	return iio_backend_op_call(back, chan_disable, chan);
+}
+EXPORT_SYMBOL_NS_GPL(iio_backend_chan_disable, IIO_BACKEND);
+
+static void __iio_backend_disable(void *back)
+{
+	iio_backend_void_op_call(back, disable);
+}
+
+/**
+ * devm_iio_backend_enable - Device managed backend enable
+ * @dev:	Consumer device for the backend
+ * @back:	Backend device
+ *
+ * RETURNS:
+ * 0 on success, negative error number on failure.
+ */
+int devm_iio_backend_enable(struct device *dev, struct iio_backend *back)
+{
+	int ret;
+
+	ret = iio_backend_op_call(back, enable);
+	if (ret)
+		return ret;
+
+	return devm_add_action_or_reset(dev, __iio_backend_disable, back);
+}
+EXPORT_SYMBOL_NS_GPL(devm_iio_backend_enable, IIO_BACKEND);
+
+/**
+ * iio_backend_data_format_set - Configure the channel data format
+ * @back:	Backend device
+ * @chan:	Channel number
+ * @data:	Data format
+ *
+ * Properly configure a channel with respect to the expected data format. A
+ * @struct iio_backend_data_fmt must be passed with the settings.
+ *
+ * RETURNS:
+ * 0 on success, negative error number on failure.
+ */
+int iio_backend_data_format_set(struct iio_backend *back, unsigned int chan,
+				const struct iio_backend_data_fmt *data)
+{
+	if (!data || data->type >= IIO_BACKEND_DATA_TYPE_MAX)
+		return -EINVAL;
+
+	return iio_backend_op_call(back, data_format_set, chan, data);
+}
+EXPORT_SYMBOL_NS_GPL(iio_backend_data_format_set, IIO_BACKEND);
+
+static void iio_backend_free_buffer(void *arg)
+{
+	struct iio_backend_buffer_pair *pair = arg;
+
+	iio_backend_void_op_call(pair->back, free_buffer, pair->buffer);
+}
+
+/**
+ * devm_iio_backend_request_buffer - Device managed buffer request
+ * @dev:	Consumer device for the backend
+ * @back:	Backend device
+ * @indio_dev:	IIO device
+ *
+ * Request an IIO buffer from the backend. The type of the buffer (typically
+ * INDIO_BUFFER_HARDWARE) is up to the backend to decide. This is because,
+ * normally, the backend dictates what kind of buffering we can get.
+ *
+ * The backend .free_buffer() hooks is automatically called on @dev detach.
+ *
+ * RETURNS:
+ * 0 on success, negative error number on failure.
+ */
+int devm_iio_backend_request_buffer(struct device *dev,
+				    struct iio_backend *back,
+				    struct iio_dev *indio_dev)
+{
+	struct iio_backend_buffer_pair *pair;
+	struct iio_buffer *buffer;
+
+	pair = devm_kzalloc(dev, sizeof(*pair), GFP_KERNEL);
+	if (!pair)
+		return -ENOMEM;
+
+	buffer = iio_backend_ptr_op_call(back, request_buffer, indio_dev);
+	if (IS_ERR(buffer))
+		return PTR_ERR(buffer);
+
+	/* weak reference should be all what we need */
+	pair->back = back;
+	pair->buffer = buffer;
+
+	return devm_add_action_or_reset(dev, iio_backend_free_buffer, pair);
+}
+EXPORT_SYMBOL_NS_GPL(devm_iio_backend_request_buffer, IIO_BACKEND);
+
+static void iio_backend_release(void *arg)
+{
+	struct iio_backend *back = arg;
+
+	module_put(back->owner);
+}
+
+static int __devm_iio_backend_get(struct device *dev, struct iio_backend *back)
+{
+	struct device_link *link;
+	int ret;
+
+	/*
+	 * Make sure the provider cannot be unloaded before the consumer module.
+	 * Note that device_links would still guarantee that nothing is
+	 * accessible (and breaks) but this makes it explicit that the consumer
+	 * module must be also unloaded.
+	 */
+	if (!try_module_get(back->owner))
+		return dev_err_probe(dev, -ENODEV,
+				     "Cannot get module reference\n");
+
+	ret = devm_add_action_or_reset(dev, iio_backend_release, back);
+	if (ret)
+		return ret;
+
+	link = device_link_add(dev, back->dev, DL_FLAG_AUTOREMOVE_CONSUMER);
+	if (!link)
+		return dev_err_probe(dev, -EINVAL,
+				     "Could not link to supplier(%s)\n",
+				     dev_name(back->dev));
+
+	dev_dbg(dev, "Found backend(%s) device\n", dev_name(back->dev));
+
+	return 0;
+}
+
+/**
+ * devm_iio_backend_get - Device managed backend device get
+ * @dev:	Consumer device for the backend
+ * @name:	Backend name
+ *
+ * Get's the backend associated with @dev.
+ *
+ * RETURNS:
+ * A backend pointer, negative error pointer otherwise.
+ */
+struct iio_backend *devm_iio_backend_get(struct device *dev, const char *name)
+{
+	struct fwnode_handle *fwnode;
+	struct iio_backend *back;
+	unsigned int index;
+	int ret;
+
+	if (name) {
+		ret = device_property_match_string(dev, "io-backend-names",
+						   name);
+		if (ret < 0)
+			return ERR_PTR(ret);
+		index = ret;
+	} else {
+		index = 0;
+	}
+
+	fwnode = fwnode_find_reference(dev_fwnode(dev), "io-backends", index);
+	if (IS_ERR(fwnode)) {
+		dev_err_probe(dev, PTR_ERR(fwnode),
+			      "Cannot get Firmware reference\n");
+		return ERR_CAST(fwnode);
+	}
+
+	guard(mutex)(&iio_back_lock);
+	list_for_each_entry(back, &iio_back_list, entry) {
+		if (!device_match_fwnode(back->dev, fwnode))
+			continue;
+
+		fwnode_handle_put(fwnode);
+		ret = __devm_iio_backend_get(dev, back);
+		if (ret)
+			return ERR_PTR(ret);
+
+		return back;
+	}
+
+	fwnode_handle_put(fwnode);
+	return ERR_PTR(-EPROBE_DEFER);
+}
+EXPORT_SYMBOL_NS_GPL(devm_iio_backend_get, IIO_BACKEND);
+
+/**
+ * __devm_iio_backend_get_from_fwnode_lookup - Device managed fwnode backend device get
+ * @dev:	Consumer device for the backend
+ * @fwnode:	Firmware node of the backend device
+ *
+ * Search the backend list for a device matching @fwnode.
+ * This API should not be used and it's only present for preventing the first
+ * user of this framework to break it's DT ABI.
+ *
+ * RETURNS:
+ * A backend pointer, negative error pointer otherwise.
+ */
+struct iio_backend *
+__devm_iio_backend_get_from_fwnode_lookup(struct device *dev,
+					  struct fwnode_handle *fwnode)
+{
+	struct iio_backend *back;
+	int ret;
+
+	guard(mutex)(&iio_back_lock);
+	list_for_each_entry(back, &iio_back_list, entry) {
+		if (!device_match_fwnode(back->dev, fwnode))
+			continue;
+
+		ret = __devm_iio_backend_get(dev, back);
+		if (ret)
+			return ERR_PTR(ret);
+
+		return back;
+	}
+
+	return ERR_PTR(-EPROBE_DEFER);
+}
+EXPORT_SYMBOL_NS_GPL(__devm_iio_backend_get_from_fwnode_lookup, IIO_BACKEND);
+
+/**
+ * iio_backend_get_priv - Get driver private data
+ * @back:	Backend device
+ */
+void *iio_backend_get_priv(const struct iio_backend *back)
+{
+	return back->priv;
+}
+EXPORT_SYMBOL_NS_GPL(iio_backend_get_priv, IIO_BACKEND);
+
+static void iio_backend_unregister(void *arg)
+{
+	struct iio_backend *back = arg;
+
+	guard(mutex)(&iio_back_lock);
+	list_del(&back->entry);
+}
+
+/**
+ * devm_iio_backend_register - Device managed backend device register
+ * @dev:	Backend device being registered
+ * @ops:	Backend ops
+ * @priv:	Device private data
+ *
+ * @ops is mandatory. Not providing it results in -EINVAL.
+ *
+ * RETURNS:
+ * 0 on success, negative error number on failure.
+ */
+int devm_iio_backend_register(struct device *dev,
+			      const struct iio_backend_ops *ops, void *priv)
+{
+	struct iio_backend *back;
+
+	if (!ops)
+		return dev_err_probe(dev, -EINVAL, "No backend ops given\n");
+
+	/*
+	 * Through device_links, we guarantee that a frontend device cannot be
+	 * bound/exist if the backend driver is not around. Hence, we can bind
+	 * the backend object lifetime with the device being passed since
+	 * removing it will tear the frontend/consumer down.
+	 */
+	back = devm_kzalloc(dev, sizeof(*back), GFP_KERNEL);
+	if (!back)
+		return -ENOMEM;
+
+	back->ops = ops;
+	back->owner = dev->driver->owner;
+	back->dev = dev;
+	back->priv = priv;
+	scoped_guard(mutex, &iio_back_lock)
+		list_add(&back->entry, &iio_back_list);
+
+	return devm_add_action_or_reset(dev, iio_backend_unregister, back);
+}
+EXPORT_SYMBOL_NS_GPL(devm_iio_backend_register, IIO_BACKEND);
+
+MODULE_AUTHOR("Nuno Sa <nuno.sa@analog.com>");
+MODULE_DESCRIPTION("Framework to handle complex IIO aggregate devices");
+MODULE_LICENSE("GPL");
diff --git a/include/linux/iio/backend.h b/include/linux/iio/backend.h
new file mode 100644
index 000000000000..a6d79381866e
--- /dev/null
+++ b/include/linux/iio/backend.h
@@ -0,0 +1,72 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef _IIO_BACKEND_H_
+#define _IIO_BACKEND_H_
+
+#include <linux/types.h>
+
+struct fwnode_handle;
+struct iio_backend;
+struct device;
+struct iio_dev;
+
+enum iio_backend_data_type {
+	IIO_BACKEND_TWOS_COMPLEMENT,
+	IIO_BACKEND_OFFSET_BINARY,
+	IIO_BACKEND_DATA_TYPE_MAX
+};
+
+/**
+ * struct iio_backend_data_fmt - Backend data format
+ * @type:		Data type.
+ * @sign_extend:	Bool to tell if the data is sign extended.
+ * @enable:		Enable/Disable the data format module. If disabled,
+ *			not formatting will happen.
+ */
+struct iio_backend_data_fmt {
+	enum iio_backend_data_type type;
+	bool sign_extend;
+	bool enable;
+};
+
+/**
+ * struct iio_backend_ops - operations structure for an iio_backend
+ * @enable:		Enable backend.
+ * @disable:		Disable backend.
+ * @chan_enable:	Enable one channel.
+ * @chan_disable:	Disable one channel.
+ * @data_format_set:	Configure the data format for a specific channel.
+ * @request_buffer:	Request an IIO buffer.
+ * @free_buffer:	Free an IIO buffer.
+ **/
+struct iio_backend_ops {
+	int (*enable)(struct iio_backend *back);
+	void (*disable)(struct iio_backend *back);
+	int (*chan_enable)(struct iio_backend *back, unsigned int chan);
+	int (*chan_disable)(struct iio_backend *back, unsigned int chan);
+	int (*data_format_set)(struct iio_backend *back, unsigned int chan,
+			       const struct iio_backend_data_fmt *data);
+	struct iio_buffer *(*request_buffer)(struct iio_backend *back,
+					     struct iio_dev *indio_dev);
+	void (*free_buffer)(struct iio_backend *back,
+			    struct iio_buffer *buffer);
+};
+
+int iio_backend_chan_enable(struct iio_backend *back, unsigned int chan);
+int iio_backend_chan_disable(struct iio_backend *back, unsigned int chan);
+int devm_iio_backend_enable(struct device *dev, struct iio_backend *back);
+int iio_backend_data_format_set(struct iio_backend *back, unsigned int chan,
+				const struct iio_backend_data_fmt *data);
+int devm_iio_backend_request_buffer(struct device *dev,
+				    struct iio_backend *back,
+				    struct iio_dev *indio_dev);
+
+void *iio_backend_get_priv(const struct iio_backend *conv);
+struct iio_backend *devm_iio_backend_get(struct device *dev, const char *name);
+struct iio_backend *
+__devm_iio_backend_get_from_fwnode_lookup(struct device *dev,
+					  struct fwnode_handle *fwnode);
+
+int devm_iio_backend_register(struct device *dev,
+			      const struct iio_backend_ops *ops, void *priv);
+
+#endif

-- 
2.43.0

[PATCH v10 6/7] iio: adc: ad9467: convert to backend framework

[Nuno Sa]

Convert the driver to use the new IIO backend framework. The device
functionality is expected to be the same (meaning no added or removed
features).

Also note this patch effectively breaks ABI and that's needed so we can
properly support this device and add needed features making use of the
new IIO framework.

Given the lack of features (and devices supported) in the ad9467 driver
compared with the ADI out of tree version, we don't expect any user of
the upstream driver so no one should notice the ABI breakage. However,
if someone is affected by this, ADI will happily support transitioning
to the backend framework.

Signed-off-by: Nuno Sa <nuno.sa@analog.com>
---
 drivers/iio/adc/Kconfig  |   2 +-
 drivers/iio/adc/ad9467.c | 267 +++++++++++++++++++++++++++++++----------------
 2 files changed, 178 insertions(+), 91 deletions(-)

diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
index 59ae1d17b50d..61736dc21d2a 100644
--- a/drivers/iio/adc/Kconfig
+++ b/drivers/iio/adc/Kconfig
@@ -307,7 +307,7 @@ config AD799X
 config AD9467
 	tristate "Analog Devices AD9467 High Speed ADC driver"
 	depends on SPI
-	depends on ADI_AXI_ADC
+	select IIO_BACKEND
 	help
 	  Say yes here to build support for Analog Devices:
 	  * AD9467 16-Bit, 200 MSPS/250 MSPS Analog-to-Digital Converter
diff --git a/drivers/iio/adc/ad9467.c b/drivers/iio/adc/ad9467.c
index 6581fce4ba95..80b9e891c848 100644
--- a/drivers/iio/adc/ad9467.c
+++ b/drivers/iio/adc/ad9467.c
@@ -17,13 +17,12 @@
 #include <linux/of.h>
 
 
+#include <linux/iio/backend.h>
 #include <linux/iio/iio.h>
 #include <linux/iio/sysfs.h>
 
 #include <linux/clk.h>
 
-#include <linux/iio/adc/adi-axi-adc.h>
-
 /*
  * ADI High-Speed ADC common spi interface registers
  * See Application-Note AN-877:
@@ -102,15 +101,20 @@
 #define AD9467_REG_VREF_MASK		0x0F
 
 struct ad9467_chip_info {
-	struct adi_axi_adc_chip_info	axi_adc_info;
-	unsigned int			default_output_mode;
-	unsigned int			vref_mask;
+	const char		*name;
+	unsigned int		id;
+	const struct		iio_chan_spec *channels;
+	unsigned int		num_channels;
+	const unsigned int	(*scale_table)[2];
+	int			num_scales;
+	unsigned long		max_rate;
+	unsigned int		default_output_mode;
+	unsigned int		vref_mask;
 };
 
-#define to_ad9467_chip_info(_info)	\
-	container_of(_info, struct ad9467_chip_info, axi_adc_info)
-
 struct ad9467_state {
+	const struct ad9467_chip_info	*info;
+	struct iio_backend		*back;
 	struct spi_device		*spi;
 	struct clk			*clk;
 	unsigned int			output_mode;
@@ -151,10 +155,10 @@ static int ad9467_spi_write(struct spi_device *spi, unsigned int reg,
 	return spi_write(spi, buf, ARRAY_SIZE(buf));
 }
 
-static int ad9467_reg_access(struct adi_axi_adc_conv *conv, unsigned int reg,
+static int ad9467_reg_access(struct iio_dev *indio_dev, unsigned int reg,
 			     unsigned int writeval, unsigned int *readval)
 {
-	struct ad9467_state *st = adi_axi_adc_conv_priv(conv);
+	struct ad9467_state *st = iio_priv(indio_dev);
 	struct spi_device *spi = st->spi;
 	int ret;
 
@@ -191,10 +195,10 @@ static const unsigned int ad9467_scale_table[][2] = {
 	{2300, 8}, {2400, 9}, {2500, 10},
 };
 
-static void __ad9467_get_scale(struct adi_axi_adc_conv *conv, int index,
+static void __ad9467_get_scale(struct ad9467_state *st, int index,
 			       unsigned int *val, unsigned int *val2)
 {
-	const struct adi_axi_adc_chip_info *info = conv->chip_info;
+	const struct ad9467_chip_info *info = st->info;
 	const struct iio_chan_spec *chan = &info->channels[0];
 	unsigned int tmp;
 
@@ -229,52 +233,44 @@ static const struct iio_chan_spec ad9467_channels[] = {
 };
 
 static const struct ad9467_chip_info ad9467_chip_tbl = {
-	.axi_adc_info = {
-		.name = "ad9467",
-		.id = CHIPID_AD9467,
-		.max_rate = 250000000UL,
-		.scale_table = ad9467_scale_table,
-		.num_scales = ARRAY_SIZE(ad9467_scale_table),
-		.channels = ad9467_channels,
-		.num_channels = ARRAY_SIZE(ad9467_channels),
-	},
+	.name = "ad9467",
+	.id = CHIPID_AD9467,
+	.max_rate = 250000000UL,
+	.scale_table = ad9467_scale_table,
+	.num_scales = ARRAY_SIZE(ad9467_scale_table),
+	.channels = ad9467_channels,
+	.num_channels = ARRAY_SIZE(ad9467_channels),
 	.default_output_mode = AD9467_DEF_OUTPUT_MODE,
 	.vref_mask = AD9467_REG_VREF_MASK,
 };
 
 static const struct ad9467_chip_info ad9434_chip_tbl = {
-	.axi_adc_info = {
-		.name = "ad9434",
-		.id = CHIPID_AD9434,
-		.max_rate = 500000000UL,
-		.scale_table = ad9434_scale_table,
-		.num_scales = ARRAY_SIZE(ad9434_scale_table),
-		.channels = ad9434_channels,
-		.num_channels = ARRAY_SIZE(ad9434_channels),
-	},
+	.name = "ad9434",
+	.id = CHIPID_AD9434,
+	.max_rate = 500000000UL,
+	.scale_table = ad9434_scale_table,
+	.num_scales = ARRAY_SIZE(ad9434_scale_table),
+	.channels = ad9434_channels,
+	.num_channels = ARRAY_SIZE(ad9434_channels),
 	.default_output_mode = AD9434_DEF_OUTPUT_MODE,
 	.vref_mask = AD9434_REG_VREF_MASK,
 };
 
 static const struct ad9467_chip_info ad9265_chip_tbl = {
-	.axi_adc_info = {
-		.name = "ad9265",
-		.id = CHIPID_AD9265,
-		.max_rate = 125000000UL,
-		.scale_table = ad9265_scale_table,
-		.num_scales = ARRAY_SIZE(ad9265_scale_table),
-		.channels = ad9467_channels,
-		.num_channels = ARRAY_SIZE(ad9467_channels),
-	},
+	.name = "ad9265",
+	.id = CHIPID_AD9265,
+	.max_rate = 125000000UL,
+	.scale_table = ad9265_scale_table,
+	.num_scales = ARRAY_SIZE(ad9265_scale_table),
+	.channels = ad9467_channels,
+	.num_channels = ARRAY_SIZE(ad9467_channels),
 	.default_output_mode = AD9265_DEF_OUTPUT_MODE,
 	.vref_mask = AD9265_REG_VREF_MASK,
 };
 
-static int ad9467_get_scale(struct adi_axi_adc_conv *conv, int *val, int *val2)
+static int ad9467_get_scale(struct ad9467_state *st, int *val, int *val2)
 {
-	const struct adi_axi_adc_chip_info *info = conv->chip_info;
-	const struct ad9467_chip_info *info1 = to_ad9467_chip_info(info);
-	struct ad9467_state *st = adi_axi_adc_conv_priv(conv);
+	const struct ad9467_chip_info *info = st->info;
 	unsigned int i, vref_val;
 	int ret;
 
@@ -282,7 +278,7 @@ static int ad9467_get_scale(struct adi_axi_adc_conv *conv, int *val, int *val2)
 	if (ret < 0)
 		return ret;
 
-	vref_val = ret & info1->vref_mask;
+	vref_val = ret & info->vref_mask;
 
 	for (i = 0; i < info->num_scales; i++) {
 		if (vref_val == info->scale_table[i][1])
@@ -292,15 +288,14 @@ static int ad9467_get_scale(struct adi_axi_adc_conv *conv, int *val, int *val2)
 	if (i == info->num_scales)
 		return -ERANGE;
 
-	__ad9467_get_scale(conv, i, val, val2);
+	__ad9467_get_scale(st, i, val, val2);
 
 	return IIO_VAL_INT_PLUS_MICRO;
 }
 
-static int ad9467_set_scale(struct adi_axi_adc_conv *conv, int val, int val2)
+static int ad9467_set_scale(struct ad9467_state *st, int val, int val2)
 {
-	const struct adi_axi_adc_chip_info *info = conv->chip_info;
-	struct ad9467_state *st = adi_axi_adc_conv_priv(conv);
+	const struct ad9467_chip_info *info = st->info;
 	unsigned int scale_val[2];
 	unsigned int i;
 	int ret;
@@ -309,7 +304,7 @@ static int ad9467_set_scale(struct adi_axi_adc_conv *conv, int val, int val2)
 		return -EINVAL;
 
 	for (i = 0; i < info->num_scales; i++) {
-		__ad9467_get_scale(conv, i, &scale_val[0], &scale_val[1]);
+		__ad9467_get_scale(st, i, &scale_val[0], &scale_val[1]);
 		if (scale_val[0] != val || scale_val[1] != val2)
 			continue;
 
@@ -326,15 +321,15 @@ static int ad9467_set_scale(struct adi_axi_adc_conv *conv, int val, int val2)
 	return -EINVAL;
 }
 
-static int ad9467_read_raw(struct adi_axi_adc_conv *conv,
+static int ad9467_read_raw(struct iio_dev *indio_dev,
 			   struct iio_chan_spec const *chan,
 			   int *val, int *val2, long m)
 {
-	struct ad9467_state *st = adi_axi_adc_conv_priv(conv);
+	struct ad9467_state *st = iio_priv(indio_dev);
 
 	switch (m) {
 	case IIO_CHAN_INFO_SCALE:
-		return ad9467_get_scale(conv, val, val2);
+		return ad9467_get_scale(st, val, val2);
 	case IIO_CHAN_INFO_SAMP_FREQ:
 		*val = clk_get_rate(st->clk);
 
@@ -344,17 +339,17 @@ static int ad9467_read_raw(struct adi_axi_adc_conv *conv,
 	}
 }
 
-static int ad9467_write_raw(struct adi_axi_adc_conv *conv,
+static int ad9467_write_raw(struct iio_dev *indio_dev,
 			    struct iio_chan_spec const *chan,
 			    int val, int val2, long mask)
 {
-	const struct adi_axi_adc_chip_info *info = conv->chip_info;
-	struct ad9467_state *st = adi_axi_adc_conv_priv(conv);
+	struct ad9467_state *st = iio_priv(indio_dev);
+	const struct ad9467_chip_info *info = st->info;
 	long r_clk;
 
 	switch (mask) {
 	case IIO_CHAN_INFO_SCALE:
-		return ad9467_set_scale(conv, val, val2);
+		return ad9467_set_scale(st, val, val2);
 	case IIO_CHAN_INFO_SAMP_FREQ:
 		r_clk = clk_round_rate(st->clk, val);
 		if (r_clk < 0 || r_clk > info->max_rate) {
@@ -369,13 +364,13 @@ static int ad9467_write_raw(struct adi_axi_adc_conv *conv,
 	}
 }
 
-static int ad9467_read_avail(struct adi_axi_adc_conv *conv,
+static int ad9467_read_avail(struct iio_dev *indio_dev,
 			     struct iio_chan_spec const *chan,
 			     const int **vals, int *type, int *length,
 			     long mask)
 {
-	const struct adi_axi_adc_chip_info *info = conv->chip_info;
-	struct ad9467_state *st = adi_axi_adc_conv_priv(conv);
+	struct ad9467_state *st = iio_priv(indio_dev);
+	const struct ad9467_chip_info *info = st->info;
 
 	switch (mask) {
 	case IIO_CHAN_INFO_SCALE:
@@ -389,6 +384,33 @@ static int ad9467_read_avail(struct adi_axi_adc_conv *conv,
 	}
 }
 
+static int ad9467_update_scan_mode(struct iio_dev *indio_dev,
+				   const unsigned long *scan_mask)
+{
+	struct ad9467_state *st = iio_priv(indio_dev);
+	unsigned int c;
+	int ret;
+
+	for (c = 0; c < st->info->num_channels; c++) {
+		if (test_bit(c, scan_mask))
+			ret = iio_backend_chan_enable(st->back, c);
+		else
+			ret = iio_backend_chan_disable(st->back, c);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
+static const struct iio_info ad9467_info = {
+	.read_raw = ad9467_read_raw,
+	.write_raw = ad9467_write_raw,
+	.update_scan_mode = ad9467_update_scan_mode,
+	.debugfs_reg_access = ad9467_reg_access,
+	.read_avail = ad9467_read_avail,
+};
+
 static int ad9467_outputmode_set(struct spi_device *spi, unsigned int mode)
 {
 	int ret;
@@ -401,10 +423,9 @@ static int ad9467_outputmode_set(struct spi_device *spi, unsigned int mode)
 				AN877_ADC_TRANSFER_SYNC);
 }
 
-static int ad9467_scale_fill(struct adi_axi_adc_conv *conv)
+static int ad9467_scale_fill(struct ad9467_state *st)
 {
-	const struct adi_axi_adc_chip_info *info = conv->chip_info;
-	struct ad9467_state *st = adi_axi_adc_conv_priv(conv);
+	const struct ad9467_chip_info *info = st->info;
 	unsigned int i, val1, val2;
 
 	st->scales = devm_kmalloc_array(&st->spi->dev, info->num_scales,
@@ -413,7 +434,7 @@ static int ad9467_scale_fill(struct adi_axi_adc_conv *conv)
 		return -ENOMEM;
 
 	for (i = 0; i < info->num_scales; i++) {
-		__ad9467_get_scale(conv, i, &val1, &val2);
+		__ad9467_get_scale(st, i, &val1, &val2);
 		st->scales[i][0] = val1;
 		st->scales[i][1] = val2;
 	}
@@ -421,11 +442,27 @@ static int ad9467_scale_fill(struct adi_axi_adc_conv *conv)
 	return 0;
 }
 
-static int ad9467_preenable_setup(struct adi_axi_adc_conv *conv)
+static int ad9467_setup(struct ad9467_state *st)
 {
-	struct ad9467_state *st = adi_axi_adc_conv_priv(conv);
+	struct iio_backend_data_fmt data = {
+		.sign_extend = true,
+		.enable = true,
+	};
+	unsigned int c, mode;
+	int ret;
+
+	mode = st->info->default_output_mode | AN877_ADC_OUTPUT_MODE_TWOS_COMPLEMENT;
+	ret = ad9467_outputmode_set(st->spi, mode);
+	if (ret)
+		return ret;
 
-	return ad9467_outputmode_set(st->spi, st->output_mode);
+	for (c = 0; c < st->info->num_channels; c++) {
+		ret = iio_backend_data_format_set(st->back, c, &data);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
 }
 
 static int ad9467_reset(struct device *dev)
@@ -443,25 +480,65 @@ static int ad9467_reset(struct device *dev)
 	return 0;
 }
 
+static int ad9467_iio_backend_get(struct ad9467_state *st)
+{
+	struct device *dev = &st->spi->dev;
+	struct device_node *__back;
+
+	st->back = devm_iio_backend_get(&st->spi->dev, NULL);
+	/* If not found, don't error out as we might have legacy DT property */
+	if (!IS_ERR(st->back))
+		return 0;
+	if (PTR_ERR(st->back) != -ENOENT)
+		return PTR_ERR(st->back);
+
+	/*
+	 * if we don't get the backend using the normal API's, use the legacy
+	 * 'adi,adc-dev' property. So we get all nodes with that property, and
+	 * look for the one pointing at us. Then we directly lookup that fwnode
+	 * on the backend list of registered devices. This is done so we don't
+	 * make io-backends mandatory which would break DT ABI.
+	 */
+	for_each_node_with_property(__back, "adi,adc-dev") {
+		struct device_node *__me;
+
+		__me = of_parse_phandle(__back, "adi,adc-dev", 0);
+		if (!__me)
+			continue;
+
+		if (!device_match_of_node(dev, __me)) {
+			of_node_put(__me);
+			continue;
+		}
+
+		of_node_put(__me);
+		st->back = __devm_iio_backend_get_from_fwnode_lookup(dev,
+								     of_fwnode_handle(__back));
+		of_node_put(__back);
+		return PTR_ERR_OR_ZERO(st->back);
+	}
+
+	return -ENODEV;
+}
+
 static int ad9467_probe(struct spi_device *spi)
 {
-	const struct ad9467_chip_info *info;
-	struct adi_axi_adc_conv *conv;
+	struct iio_dev *indio_dev;
 	struct ad9467_state *st;
 	unsigned int id;
 	int ret;
 
-	info = spi_get_device_match_data(spi);
-	if (!info)
-		return -ENODEV;
-
-	conv = devm_adi_axi_adc_conv_register(&spi->dev, sizeof(*st));
-	if (IS_ERR(conv))
-		return PTR_ERR(conv);
+	indio_dev = devm_iio_device_alloc(&spi->dev, sizeof(*st));
+	if (!indio_dev)
+		return -ENOMEM;
 
-	st = adi_axi_adc_conv_priv(conv);
+	st = iio_priv(indio_dev);
 	st->spi = spi;
 
+	st->info = spi_get_device_match_data(spi);
+	if (!st->info)
+		return -ENODEV;
+
 	st->clk = devm_clk_get_enabled(&spi->dev, "adc-clk");
 	if (IS_ERR(st->clk))
 		return PTR_ERR(st->clk);
@@ -475,29 +552,39 @@ static int ad9467_probe(struct spi_device *spi)
 	if (ret)
 		return ret;
 
-	conv->chip_info = &info->axi_adc_info;
-
-	ret = ad9467_scale_fill(conv);
+	ret = ad9467_scale_fill(st);
 	if (ret)
 		return ret;
 
 	id = ad9467_spi_read(spi, AN877_ADC_REG_CHIP_ID);
-	if (id != conv->chip_info->id) {
+	if (id != st->info->id) {
 		dev_err(&spi->dev, "Mismatch CHIP_ID, got 0x%X, expected 0x%X\n",
-			id, conv->chip_info->id);
+			id, st->info->id);
 		return -ENODEV;
 	}
 
-	conv->reg_access = ad9467_reg_access;
-	conv->write_raw = ad9467_write_raw;
-	conv->read_raw = ad9467_read_raw;
-	conv->read_avail = ad9467_read_avail;
-	conv->preenable_setup = ad9467_preenable_setup;
+	indio_dev->name = st->info->name;
+	indio_dev->channels = st->info->channels;
+	indio_dev->num_channels = st->info->num_channels;
+	indio_dev->info = &ad9467_info;
 
-	st->output_mode = info->default_output_mode |
-			  AN877_ADC_OUTPUT_MODE_TWOS_COMPLEMENT;
+	ret = ad9467_iio_backend_get(st);
+	if (ret)
+		return ret;
 
-	return 0;
+	ret = devm_iio_backend_request_buffer(&spi->dev, st->back, indio_dev);
+	if (ret)
+		return ret;
+
+	ret = devm_iio_backend_enable(&spi->dev, st->back);
+	if (ret)
+		return ret;
+
+	ret = ad9467_setup(st);
+	if (ret)
+		return ret;
+
+	return devm_iio_device_register(&spi->dev, indio_dev);
 }
 
 static const struct of_device_id ad9467_of_match[] = {
@@ -529,4 +616,4 @@ module_spi_driver(ad9467_driver);
 MODULE_AUTHOR("Michael Hennerich <michael.hennerich@analog.com>");
 MODULE_DESCRIPTION("Analog Devices AD9467 ADC driver");
 MODULE_LICENSE("GPL v2");
-MODULE_IMPORT_NS(IIO_ADI_AXI);
+MODULE_IMPORT_NS(IIO_BACKEND);

-- 
2.43.0

[PATCH v10 7/7] iio: adc: adi-axi-adc: move to backend framework

[Nuno Sa]

Move to the IIO backend framework. Devices supported by adi-axi-adc now
register themselves as backend devices.

Signed-off-by: Nuno Sa <nuno.sa@analog.com>
---
 drivers/iio/adc/Kconfig             |   2 +-
 drivers/iio/adc/adi-axi-adc.c       | 378 +++++++++---------------------------
 include/linux/iio/adc/adi-axi-adc.h |  68 -------
 3 files changed, 92 insertions(+), 356 deletions(-)

diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
index 61736dc21d2a..977832d797e1 100644
--- a/drivers/iio/adc/Kconfig
+++ b/drivers/iio/adc/Kconfig
@@ -325,7 +325,7 @@ config ADI_AXI_ADC
 	select IIO_BUFFER_HW_CONSUMER
 	select IIO_BUFFER_DMAENGINE
 	select REGMAP_MMIO
-	depends on OF
+	select IIO_BACKEND
 	help
 	  Say yes here to build support for Analog Devices Generic
 	  AXI ADC IP core. The IP core is used for interfacing with
diff --git a/drivers/iio/adc/adi-axi-adc.c b/drivers/iio/adc/adi-axi-adc.c
index 0f21d1d98b9f..cb28b25e97a4 100644
--- a/drivers/iio/adc/adi-axi-adc.c
+++ b/drivers/iio/adc/adi-axi-adc.c
@@ -8,6 +8,7 @@
 
 #include <linux/bitfield.h>
 #include <linux/clk.h>
+#include <linux/err.h>
 #include <linux/io.h>
 #include <linux/delay.h>
 #include <linux/module.h>
@@ -17,13 +18,11 @@
 #include <linux/regmap.h>
 #include <linux/slab.h>
 
-#include <linux/iio/iio.h>
-#include <linux/iio/sysfs.h>
-#include <linux/iio/buffer.h>
-#include <linux/iio/buffer-dmaengine.h>
-
 #include <linux/fpga/adi-axi-common.h>
-#include <linux/iio/adc/adi-axi-adc.h>
+#include <linux/iio/backend.h>
+#include <linux/iio/buffer-dmaengine.h>
+#include <linux/iio/buffer.h>
+#include <linux/iio/iio.h>
 
 /*
  * Register definitions:
@@ -44,6 +43,7 @@
 #define   ADI_AXI_REG_CHAN_CTRL_PN_SEL_OWR	BIT(10)
 #define   ADI_AXI_REG_CHAN_CTRL_IQCOR_EN	BIT(9)
 #define   ADI_AXI_REG_CHAN_CTRL_DCFILT_EN	BIT(8)
+#define   ADI_AXI_REG_CHAN_CTRL_FMT_MASK	GENMASK(6, 4)
 #define   ADI_AXI_REG_CHAN_CTRL_FMT_SIGNEXT	BIT(6)
 #define   ADI_AXI_REG_CHAN_CTRL_FMT_TYPE	BIT(5)
 #define   ADI_AXI_REG_CHAN_CTRL_FMT_EN		BIT(4)
@@ -55,286 +55,100 @@
 	 ADI_AXI_REG_CHAN_CTRL_FMT_EN |		\
 	 ADI_AXI_REG_CHAN_CTRL_ENABLE)
 
-struct adi_axi_adc_core_info {
-	unsigned int				version;
-};
-
 struct adi_axi_adc_state {
-	struct mutex				lock;
-
-	struct adi_axi_adc_client		*client;
 	struct regmap				*regmap;
-};
-
-struct adi_axi_adc_client {
-	struct list_head			entry;
-	struct adi_axi_adc_conv			conv;
-	struct adi_axi_adc_state		*state;
 	struct device				*dev;
-	const struct adi_axi_adc_core_info	*info;
 };
 
-static LIST_HEAD(registered_clients);
-static DEFINE_MUTEX(registered_clients_lock);
-
-static struct adi_axi_adc_client *conv_to_client(struct adi_axi_adc_conv *conv)
-{
-	return container_of(conv, struct adi_axi_adc_client, conv);
-}
-
-void *adi_axi_adc_conv_priv(struct adi_axi_adc_conv *conv)
-{
-	struct adi_axi_adc_client *cl = conv_to_client(conv);
-
-	return (char *)cl + ALIGN(sizeof(struct adi_axi_adc_client),
-				  IIO_DMA_MINALIGN);
-}
-EXPORT_SYMBOL_NS_GPL(adi_axi_adc_conv_priv, IIO_ADI_AXI);
-
-static int adi_axi_adc_config_dma_buffer(struct device *dev,
-					 struct iio_dev *indio_dev)
-{
-	const char *dma_name;
-
-	if (!device_property_present(dev, "dmas"))
-		return 0;
-
-	if (device_property_read_string(dev, "dma-names", &dma_name))
-		dma_name = "rx";
-
-	return devm_iio_dmaengine_buffer_setup(indio_dev->dev.parent,
-					       indio_dev, dma_name);
-}
-
-static int adi_axi_adc_read_raw(struct iio_dev *indio_dev,
-				struct iio_chan_spec const *chan,
-				int *val, int *val2, long mask)
-{
-	struct adi_axi_adc_state *st = iio_priv(indio_dev);
-	struct adi_axi_adc_conv *conv = &st->client->conv;
-
-	if (!conv->read_raw)
-		return -EOPNOTSUPP;
-
-	return conv->read_raw(conv, chan, val, val2, mask);
-}
-
-static int adi_axi_adc_write_raw(struct iio_dev *indio_dev,
-				 struct iio_chan_spec const *chan,
-				 int val, int val2, long mask)
-{
-	struct adi_axi_adc_state *st = iio_priv(indio_dev);
-	struct adi_axi_adc_conv *conv = &st->client->conv;
-
-	if (!conv->write_raw)
-		return -EOPNOTSUPP;
-
-	return conv->write_raw(conv, chan, val, val2, mask);
-}
-
-static int adi_axi_adc_read_avail(struct iio_dev *indio_dev,
-				  struct iio_chan_spec const *chan,
-				  const int **vals, int *type, int *length,
-				  long mask)
+static int axi_adc_enable(struct iio_backend *back)
 {
-	struct adi_axi_adc_state *st = iio_priv(indio_dev);
-	struct adi_axi_adc_conv *conv = &st->client->conv;
-
-	if (!conv->read_avail)
-		return -EOPNOTSUPP;
-
-	return conv->read_avail(conv, chan, vals, type, length, mask);
-}
-
-static int adi_axi_adc_update_scan_mode(struct iio_dev *indio_dev,
-					const unsigned long *scan_mask)
-{
-	struct adi_axi_adc_state *st = iio_priv(indio_dev);
-	struct adi_axi_adc_conv *conv = &st->client->conv;
-	unsigned int i;
+	struct adi_axi_adc_state *st = iio_backend_get_priv(back);
 	int ret;
 
-	for (i = 0; i < conv->chip_info->num_channels; i++) {
-		if (test_bit(i, scan_mask))
-			ret = regmap_set_bits(st->regmap,
-					      ADI_AXI_REG_CHAN_CTRL(i),
-					      ADI_AXI_REG_CHAN_CTRL_ENABLE);
-		else
-			ret = regmap_clear_bits(st->regmap,
-						ADI_AXI_REG_CHAN_CTRL(i),
-						ADI_AXI_REG_CHAN_CTRL_ENABLE);
-		if (ret)
-			return ret;
-	}
+	ret = regmap_set_bits(st->regmap, ADI_AXI_REG_RSTN,
+			      ADI_AXI_REG_RSTN_MMCM_RSTN);
+	if (ret)
+		return ret;
 
-	return 0;
+	fsleep(10);
+	return regmap_set_bits(st->regmap, ADI_AXI_REG_RSTN,
+			       ADI_AXI_REG_RSTN_RSTN | ADI_AXI_REG_RSTN_MMCM_RSTN);
 }
 
-static struct adi_axi_adc_conv *adi_axi_adc_conv_register(struct device *dev,
-							  size_t sizeof_priv)
+static void axi_adc_disable(struct iio_backend *back)
 {
-	struct adi_axi_adc_client *cl;
-	size_t alloc_size;
-
-	alloc_size = ALIGN(sizeof(struct adi_axi_adc_client), IIO_DMA_MINALIGN);
-	if (sizeof_priv)
-		alloc_size += ALIGN(sizeof_priv, IIO_DMA_MINALIGN);
+	struct adi_axi_adc_state *st = iio_backend_get_priv(back);
 
-	cl = kzalloc(alloc_size, GFP_KERNEL);
-	if (!cl)
-		return ERR_PTR(-ENOMEM);
-
-	mutex_lock(&registered_clients_lock);
-
-	cl->dev = get_device(dev);
-
-	list_add_tail(&cl->entry, &registered_clients);
-
-	mutex_unlock(&registered_clients_lock);
-
-	return &cl->conv;
+	regmap_write(st->regmap, ADI_AXI_REG_RSTN, 0);
 }
 
-static void adi_axi_adc_conv_unregister(struct adi_axi_adc_conv *conv)
+static int axi_adc_data_format_set(struct iio_backend *back, unsigned int chan,
+				   const struct iio_backend_data_fmt *data)
 {
-	struct adi_axi_adc_client *cl = conv_to_client(conv);
-
-	mutex_lock(&registered_clients_lock);
+	struct adi_axi_adc_state *st = iio_backend_get_priv(back);
+	u32 val;
 
-	list_del(&cl->entry);
-	put_device(cl->dev);
+	if (!data->enable)
+		return regmap_clear_bits(st->regmap,
+					 ADI_AXI_REG_CHAN_CTRL(chan),
+					 ADI_AXI_REG_CHAN_CTRL_FMT_EN);
 
-	mutex_unlock(&registered_clients_lock);
+	val = FIELD_PREP(ADI_AXI_REG_CHAN_CTRL_FMT_EN, true);
+	if (data->sign_extend)
+		val |= FIELD_PREP(ADI_AXI_REG_CHAN_CTRL_FMT_SIGNEXT, true);
+	if (data->type == IIO_BACKEND_OFFSET_BINARY)
+		val |= FIELD_PREP(ADI_AXI_REG_CHAN_CTRL_FMT_TYPE, true);
 
-	kfree(cl);
+	return regmap_update_bits(st->regmap, ADI_AXI_REG_CHAN_CTRL(chan),
+				  ADI_AXI_REG_CHAN_CTRL_FMT_MASK, val);
 }
 
-static void devm_adi_axi_adc_conv_release(void *conv)
+static int axi_adc_chan_enable(struct iio_backend *back, unsigned int chan)
 {
-	adi_axi_adc_conv_unregister(conv);
-}
-
-struct adi_axi_adc_conv *devm_adi_axi_adc_conv_register(struct device *dev,
-							size_t sizeof_priv)
-{
-	struct adi_axi_adc_conv *conv;
-	int ret;
-
-	conv = adi_axi_adc_conv_register(dev, sizeof_priv);
-	if (IS_ERR(conv))
-		return conv;
-
-	ret = devm_add_action_or_reset(dev, devm_adi_axi_adc_conv_release,
-				       conv);
-	if (ret)
-		return ERR_PTR(ret);
+	struct adi_axi_adc_state *st = iio_backend_get_priv(back);
 
-	return conv;
+	return regmap_set_bits(st->regmap, ADI_AXI_REG_CHAN_CTRL(chan),
+			       ADI_AXI_REG_CHAN_CTRL_ENABLE);
 }
-EXPORT_SYMBOL_NS_GPL(devm_adi_axi_adc_conv_register, IIO_ADI_AXI);
-
-static const struct iio_info adi_axi_adc_info = {
-	.read_raw = &adi_axi_adc_read_raw,
-	.write_raw = &adi_axi_adc_write_raw,
-	.update_scan_mode = &adi_axi_adc_update_scan_mode,
-	.read_avail = &adi_axi_adc_read_avail,
-};
 
-static const struct adi_axi_adc_core_info adi_axi_adc_10_0_a_info = {
-	.version = ADI_AXI_PCORE_VER(10, 0, 'a'),
-};
-
-static struct adi_axi_adc_client *adi_axi_adc_attach_client(struct device *dev)
+static int axi_adc_chan_disable(struct iio_backend *back, unsigned int chan)
 {
-	const struct adi_axi_adc_core_info *info;
-	struct adi_axi_adc_client *cl;
-	struct device_node *cln;
-
-	info = of_device_get_match_data(dev);
-	if (!info)
-		return ERR_PTR(-ENODEV);
-
-	cln = of_parse_phandle(dev->of_node, "adi,adc-dev", 0);
-	if (!cln) {
-		dev_err(dev, "No 'adi,adc-dev' node defined\n");
-		return ERR_PTR(-ENODEV);
-	}
-
-	mutex_lock(&registered_clients_lock);
+	struct adi_axi_adc_state *st = iio_backend_get_priv(back);
 
-	list_for_each_entry(cl, &registered_clients, entry) {
-		if (!cl->dev)
-			continue;
-
-		if (cl->dev->of_node != cln)
-			continue;
-
-		if (!try_module_get(cl->dev->driver->owner)) {
-			mutex_unlock(&registered_clients_lock);
-			of_node_put(cln);
-			return ERR_PTR(-ENODEV);
-		}
-
-		get_device(cl->dev);
-		cl->info = info;
-		mutex_unlock(&registered_clients_lock);
-		of_node_put(cln);
-		return cl;
-	}
-
-	mutex_unlock(&registered_clients_lock);
-	of_node_put(cln);
-
-	return ERR_PTR(-EPROBE_DEFER);
+	return regmap_clear_bits(st->regmap, ADI_AXI_REG_CHAN_CTRL(chan),
+				 ADI_AXI_REG_CHAN_CTRL_ENABLE);
 }
 
-static int adi_axi_adc_setup_channels(struct device *dev,
-				      struct adi_axi_adc_state *st)
+static struct iio_buffer *axi_adc_request_buffer(struct iio_backend *back,
+						 struct iio_dev *indio_dev)
 {
-	struct adi_axi_adc_conv *conv = &st->client->conv;
-	int i, ret;
+	struct adi_axi_adc_state *st = iio_backend_get_priv(back);
+	struct iio_buffer *buffer;
+	const char *dma_name;
+	int ret;
 
-	if (conv->preenable_setup) {
-		ret = conv->preenable_setup(conv);
-		if (ret)
-			return ret;
-	}
+	if (device_property_read_string(st->dev, "dma-names", &dma_name))
+		dma_name = "rx";
 
-	for (i = 0; i < conv->chip_info->num_channels; i++) {
-		ret = regmap_write(st->regmap, ADI_AXI_REG_CHAN_CTRL(i),
-				   ADI_AXI_REG_CHAN_CTRL_DEFAULTS);
-		if (ret)
-			return ret;
+	buffer = iio_dmaengine_buffer_alloc(st->dev, dma_name);
+	if (IS_ERR(buffer)) {
+		dev_err(st->dev, "Could not get DMA buffer, %ld\n",
+			PTR_ERR(buffer));
+		return ERR_CAST(buffer);
 	}
 
-	return 0;
-}
-
-static int axi_adc_reset(struct adi_axi_adc_state *st)
-{
-	int ret;
-
-	ret = regmap_write(st->regmap, ADI_AXI_REG_RSTN, 0);
-	if (ret)
-		return ret;
-
-	mdelay(10);
-	ret = regmap_write(st->regmap, ADI_AXI_REG_RSTN,
-			   ADI_AXI_REG_RSTN_MMCM_RSTN);
+	indio_dev->modes |= INDIO_BUFFER_HARDWARE;
+	ret = iio_device_attach_buffer(indio_dev, buffer);
 	if (ret)
-		return ret;
+		return ERR_PTR(ret);
 
-	mdelay(10);
-	return regmap_write(st->regmap, ADI_AXI_REG_RSTN,
-			    ADI_AXI_REG_RSTN_RSTN | ADI_AXI_REG_RSTN_MMCM_RSTN);
+	return buffer;
 }
 
-static void adi_axi_adc_cleanup(void *data)
+static void axi_adc_free_buffer(struct iio_backend *back,
+				struct iio_buffer *buffer)
 {
-	struct adi_axi_adc_client *cl = data;
-
-	put_device(cl->dev);
-	module_put(cl->dev->driver->owner);
+	iio_dmaengine_buffer_free(buffer);
 }
 
 static const struct regmap_config axi_adc_regmap_config = {
@@ -344,45 +158,46 @@ static const struct regmap_config axi_adc_regmap_config = {
 	.max_register = 0x0800,
 };
 
+static const struct iio_backend_ops adi_axi_adc_generic = {
+	.enable = axi_adc_enable,
+	.disable = axi_adc_disable,
+	.data_format_set = axi_adc_data_format_set,
+	.chan_enable = axi_adc_chan_enable,
+	.chan_disable = axi_adc_chan_disable,
+	.request_buffer = axi_adc_request_buffer,
+	.free_buffer = axi_adc_free_buffer,
+};
+
 static int adi_axi_adc_probe(struct platform_device *pdev)
 {
-	struct adi_axi_adc_conv *conv;
-	struct iio_dev *indio_dev;
-	struct adi_axi_adc_client *cl;
 	struct adi_axi_adc_state *st;
 	void __iomem *base;
-	unsigned int ver;
+	unsigned int ver, *expected_ver;
 	int ret;
 
-	cl = adi_axi_adc_attach_client(&pdev->dev);
-	if (IS_ERR(cl))
-		return PTR_ERR(cl);
-
-	ret = devm_add_action_or_reset(&pdev->dev, adi_axi_adc_cleanup, cl);
-	if (ret)
-		return ret;
-
-	indio_dev = devm_iio_device_alloc(&pdev->dev, sizeof(*st));
-	if (indio_dev == NULL)
+	st = devm_kzalloc(&pdev->dev, sizeof(*st), GFP_KERNEL);
+	if (!st)
 		return -ENOMEM;
 
-	st = iio_priv(indio_dev);
-	st->client = cl;
-	cl->state = st;
-	mutex_init(&st->lock);
-
 	base = devm_platform_ioremap_resource(pdev, 0);
 	if (IS_ERR(base))
 		return PTR_ERR(base);
 
+	st->dev = &pdev->dev;
 	st->regmap = devm_regmap_init_mmio(&pdev->dev, base,
 					   &axi_adc_regmap_config);
 	if (IS_ERR(st->regmap))
 		return PTR_ERR(st->regmap);
 
-	conv = &st->client->conv;
+	expected_ver = (unsigned int *)device_get_match_data(&pdev->dev);
+	if (!expected_ver)
+		return -ENODEV;
 
-	ret = axi_adc_reset(st);
+	/*
+	 * Force disable the core. Up to the frontend to enable us. And we can
+	 * still read/write registers...
+	 */
+	ret = regmap_write(st->regmap, ADI_AXI_REG_RSTN, 0);
 	if (ret)
 		return ret;
 
@@ -390,33 +205,19 @@ static int adi_axi_adc_probe(struct platform_device *pdev)
 	if (ret)
 		return ret;
 
-	if (cl->info->version > ver) {
+	if (*expected_ver > ver) {
 		dev_err(&pdev->dev,
 			"IP core version is too old. Expected %d.%.2d.%c, Reported %d.%.2d.%c\n",
-			ADI_AXI_PCORE_VER_MAJOR(cl->info->version),
-			ADI_AXI_PCORE_VER_MINOR(cl->info->version),
-			ADI_AXI_PCORE_VER_PATCH(cl->info->version),
+			ADI_AXI_PCORE_VER_MAJOR(*expected_ver),
+			ADI_AXI_PCORE_VER_MINOR(*expected_ver),
+			ADI_AXI_PCORE_VER_PATCH(*expected_ver),
 			ADI_AXI_PCORE_VER_MAJOR(ver),
 			ADI_AXI_PCORE_VER_MINOR(ver),
 			ADI_AXI_PCORE_VER_PATCH(ver));
 		return -ENODEV;
 	}
 
-	indio_dev->info = &adi_axi_adc_info;
-	indio_dev->name = "adi-axi-adc";
-	indio_dev->modes = INDIO_DIRECT_MODE;
-	indio_dev->num_channels = conv->chip_info->num_channels;
-	indio_dev->channels = conv->chip_info->channels;
-
-	ret = adi_axi_adc_config_dma_buffer(&pdev->dev, indio_dev);
-	if (ret)
-		return ret;
-
-	ret = adi_axi_adc_setup_channels(&pdev->dev, st);
-	if (ret)
-		return ret;
-
-	ret = devm_iio_device_register(&pdev->dev, indio_dev);
+	ret = devm_iio_backend_register(&pdev->dev, &adi_axi_adc_generic, st);
 	if (ret)
 		return ret;
 
@@ -428,6 +229,8 @@ static int adi_axi_adc_probe(struct platform_device *pdev)
 	return 0;
 }
 
+static unsigned int adi_axi_adc_10_0_a_info = ADI_AXI_PCORE_VER(10, 0, 'a');
+
 /* Match table for of_platform binding */
 static const struct of_device_id adi_axi_adc_of_match[] = {
 	{ .compatible = "adi,axi-adc-10.0.a", .data = &adi_axi_adc_10_0_a_info },
@@ -448,3 +251,4 @@ MODULE_AUTHOR("Michael Hennerich <michael.hennerich@analog.com>");
 MODULE_DESCRIPTION("Analog Devices Generic AXI ADC IP core driver");
 MODULE_LICENSE("GPL v2");
 MODULE_IMPORT_NS(IIO_DMAENGINE_BUFFER);
+MODULE_IMPORT_NS(IIO_BACKEND);
diff --git a/include/linux/iio/adc/adi-axi-adc.h b/include/linux/iio/adc/adi-axi-adc.h
deleted file mode 100644
index b7904992d561..000000000000
--- a/include/linux/iio/adc/adi-axi-adc.h
+++ /dev/null
@@ -1,68 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0 */
-/*
- * Analog Devices Generic AXI ADC IP core driver/library
- * Link: https://wiki.analog.com/resources/fpga/docs/axi_adc_ip
- *
- * Copyright 2012-2020 Analog Devices Inc.
- */
-#ifndef __ADI_AXI_ADC_H__
-#define __ADI_AXI_ADC_H__
-
-struct device;
-struct iio_chan_spec;
-
-/**
- * struct adi_axi_adc_chip_info - Chip specific information
- * @name		Chip name
- * @id			Chip ID (usually product ID)
- * @channels		Channel specifications of type @struct iio_chan_spec
- * @num_channels	Number of @channels
- * @scale_table		Supported scales by the chip; tuples of 2 ints
- * @num_scales		Number of scales in the table
- * @max_rate		Maximum sampling rate supported by the device
- */
-struct adi_axi_adc_chip_info {
-	const char			*name;
-	unsigned int			id;
-
-	const struct iio_chan_spec	*channels;
-	unsigned int			num_channels;
-
-	const unsigned int		(*scale_table)[2];
-	int				num_scales;
-
-	unsigned long			max_rate;
-};
-
-/**
- * struct adi_axi_adc_conv - data of the ADC attached to the AXI ADC
- * @chip_info		chip info details for the client ADC
- * @preenable_setup	op to run in the client before enabling the AXI ADC
- * @reg_access		IIO debugfs_reg_access hook for the client ADC
- * @read_raw		IIO read_raw hook for the client ADC
- * @write_raw		IIO write_raw hook for the client ADC
- * @read_avail		IIO read_avail hook for the client ADC
- */
-struct adi_axi_adc_conv {
-	const struct adi_axi_adc_chip_info		*chip_info;
-
-	int (*preenable_setup)(struct adi_axi_adc_conv *conv);
-	int (*reg_access)(struct adi_axi_adc_conv *conv, unsigned int reg,
-			  unsigned int writeval, unsigned int *readval);
-	int (*read_raw)(struct adi_axi_adc_conv *conv,
-			struct iio_chan_spec const *chan,
-			int *val, int *val2, long mask);
-	int (*write_raw)(struct adi_axi_adc_conv *conv,
-			 struct iio_chan_spec const *chan,
-			 int val, int val2, long mask);
-	int (*read_avail)(struct adi_axi_adc_conv *conv,
-			  struct iio_chan_spec const *chan,
-			  const int **val, int *type, int *length, long mask);
-};
-
-struct adi_axi_adc_conv *devm_adi_axi_adc_conv_register(struct device *dev,
-							size_t sizeof_priv);
-
-void *adi_axi_adc_conv_priv(struct adi_axi_adc_conv *conv);
-
-#endif

-- 
2.43.0

Re: [PATCH v10 5/7] iio: add the IIO backend framework

[Andy Shevchenko]

On Fri, Feb 9, 2024 at 5:26 PM Nuno Sa <nuno.sa@analog.com> wrote:
>
> This is a Framework to handle complex IIO aggregate devices.
>
> The typical architecture is to have one device as the frontend device which
> can be "linked" against one or multiple backend devices. All the IIO and
> userspace interface is expected to be registers/managed by the frontend
> device which will callback into the backends when needed (to get/set
> some configuration that it does not directly control).
>
> The basic framework interface is pretty simple:
>  - Backends should register themselves with @devm_iio_backend_register()
>  - Frontend devices should get backends with @devm_iio_backend_get()

...

> +       fwnode = fwnode_find_reference(dev_fwnode(dev), "io-backends", index);
> +       if (IS_ERR(fwnode)) {
> +               dev_err_probe(dev, PTR_ERR(fwnode),
> +                             "Cannot get Firmware reference\n");
> +               return ERR_CAST(fwnode);

You can combine them in one line (yeah, a bit ugly, I know, we
discussed with Andi at some point that it would be nice to have
dev_err_probe*() family of helpers for this and other not yet covered
cases). Whatever Jonathan likes (as two or a single line), I'm fine
with this, just a side note.

> +       }

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v10 5/7] iio: add the IIO backend framework

[Andy Shevchenko]

On Fri, Feb 9, 2024 at 5:26 PM Nuno Sa <nuno.sa@analog.com> wrote:

...

> +struct iio_backend *devm_iio_backend_get(struct device *dev, const char *name)
> +{
> +       struct fwnode_handle *fwnode;
> +       struct iio_backend *back;
> +       unsigned int index;
> +       int ret;
> +
> +       if (name) {
> +               ret = device_property_match_string(dev, "io-backend-names",
> +                                                  name);
> +               if (ret < 0)
> +                       return ERR_PTR(ret);
> +               index = ret;
> +       } else {
> +               index = 0;
> +       }
> +
> +       fwnode = fwnode_find_reference(dev_fwnode(dev), "io-backends", index);
> +       if (IS_ERR(fwnode)) {
> +               dev_err_probe(dev, PTR_ERR(fwnode),
> +                             "Cannot get Firmware reference\n");
> +               return ERR_CAST(fwnode);
> +       }
> +
> +       guard(mutex)(&iio_back_lock);
> +       list_for_each_entry(back, &iio_back_list, entry) {
> +               if (!device_match_fwnode(back->dev, fwnode))
> +                       continue;

> +               fwnode_handle_put(fwnode);
> +               ret = __devm_iio_backend_get(dev, back);

This order makes me think about the reference counting. So, fwnode is
the one of the backend devices to which the property points to.
Another piece is the local (to this framework) list that keeps backend
devices. So, fwnode reference can be  dropped earlier, while the usual
pattern to interleave gets and puts in a chain. Dunno if above needs a
comment, reordering or nothing.

> +               if (ret)
> +                       return ERR_PTR(ret);
> +
> +               return back;
> +       }
> +
> +       fwnode_handle_put(fwnode);
> +       return ERR_PTR(-EPROBE_DEFER);

While thinking about the above, I noticed the room to refactor.

  list_for_each_entry(...) {
    if (...)
      break;
  }
  fwnode_handle_put(...);
  // Yes, we may use the below macro as the (global) pointers are
protected by a mutex.
  if (list_entry_is_head(...))
    return ERR_PTR(...);

  ret = __devm_iio_backend_get(...);
  ...

> +}

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v10 6/7] iio: adc: ad9467: convert to backend framework

[Andy Shevchenko]

On Fri, Feb 9, 2024 at 5:26 PM Nuno Sa <nuno.sa@analog.com> wrote:
>
> Convert the driver to use the new IIO backend framework. The device
> functionality is expected to be the same (meaning no added or removed
> features).
>
> Also note this patch effectively breaks ABI and that's needed so we can
> properly support this device and add needed features making use of the
> new IIO framework.
>
> Given the lack of features (and devices supported) in the ad9467 driver
> compared with the ADI out of tree version, we don't expect any user of
> the upstream driver so no one should notice the ABI breakage. However,
> if someone is affected by this, ADI will happily support transitioning
> to the backend framework.

...

>  struct ad9467_chip_info {
> -       struct adi_axi_adc_chip_info    axi_adc_info;
> -       unsigned int                    default_output_mode;
> -       unsigned int                    vref_mask;
> +       const char              *name;
> +       unsigned int            id;
> +       const struct            iio_chan_spec *channels;
> +       unsigned int            num_channels;
> +       const unsigned int      (*scale_table)[2];
> +       int                     num_scales;
> +       unsigned long           max_rate;
> +       unsigned int            default_output_mode;
> +       unsigned int            vref_mask;
>  };

Seems like you haven't checked this layout with `pahole`.

...

> +static int ad9467_iio_backend_get(struct ad9467_state *st)
> +{
> +       struct device *dev = &st->spi->dev;
> +       struct device_node *__back;
> +
> +       st->back = devm_iio_backend_get(&st->spi->dev, NULL);

Simply 'dev' as the first parameter?

...

> +       /* If not found, don't error out as we might have legacy DT property */

This seems related to ENOENT, correct?

> +       if (!IS_ERR(st->back))
> +               return 0;

And the above is about something else (found?) case, right?

> +       if (PTR_ERR(st->back) != -ENOENT)
> +               return PTR_ERR(st->back);

--
With Best Regards,
Andy Shevchenko

Re: [PATCH v10 7/7] iio: adc: adi-axi-adc: move to backend framework

[Andy Shevchenko]

On Fri, Feb 9, 2024 at 5:26 PM Nuno Sa <nuno.sa@analog.com> wrote:
>
> Move to the IIO backend framework. Devices supported by adi-axi-adc now
> register themselves as backend devices.

...

> -#include <linux/iio/iio.h>
> -#include <linux/iio/sysfs.h>
> -#include <linux/iio/buffer.h>
> -#include <linux/iio/buffer-dmaengine.h>
> -
>  #include <linux/fpga/adi-axi-common.h>
> -#include <linux/iio/adc/adi-axi-adc.h>

+ Blank line?

> +#include <linux/iio/backend.h>
> +#include <linux/iio/buffer-dmaengine.h>
> +#include <linux/iio/buffer.h>
> +#include <linux/iio/iio.h>

...

> +static int axi_adc_enable(struct iio_backend *back)
>  {
> +       struct adi_axi_adc_state *st = iio_backend_get_priv(back);
>         int ret;
>
> +       ret = regmap_set_bits(st->regmap, ADI_AXI_REG_RSTN,
> +                             ADI_AXI_REG_RSTN_MMCM_RSTN);
> +       if (ret)
> +               return ret;

> +       fsleep(10);

Would be nice to have a comment that probably the datasheet defines
the minimum timeout for reset. Ah and you decreased it 1000x times,
why?

> +       return regmap_set_bits(st->regmap, ADI_AXI_REG_RSTN,
> +                              ADI_AXI_REG_RSTN_RSTN | ADI_AXI_REG_RSTN_MMCM_RSTN);
>  }

...

> +       expected_ver = (unsigned int *)device_get_match_data(&pdev->dev);

expected_ver should have const and you can drop the casting IIUC.

> +       if (!expected_ver)
> +               return -ENODEV;

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v10 0/7] iio: add new backend framework

[Andy Shevchenko]

On Fri, Feb 9, 2024 at 5:25 PM Nuno Sa <nuno.sa@analog.com> wrote:

> Changes in v10:
>  - Patch 5
>    * Removed meaningless @ in function names;
>    * Added ascii diagram for the typicaly HW setup (Andy request);
>    * Add missing period;
>    * Use of dev_err_probe() in APIs meant to be called during probe().
>  - Patch 6
>    * Removed unneeded blank line;
>    * Fixed some English in the commit message.

Thanks for the update!
I found it nice, only one (kinda important) finding is the 1000x reset
timeout decrease. It might justify v11. If so, consider other comments
as well.

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v10 5/7] iio: add the IIO backend framework

[Jonathan Cameron]

On Fri, 9 Feb 2024 18:30:53 +0200
Andy Shevchenko <andy.shevchenko@gmail.com> wrote:

> On Fri, Feb 9, 2024 at 5:26 PM Nuno Sa <nuno.sa@analog.com> wrote:
> 
> ...
> 
> > +struct iio_backend *devm_iio_backend_get(struct device *dev, const char *name)
> > +{
> > +       struct fwnode_handle *fwnode;
> > +       struct iio_backend *back;
> > +       unsigned int index;
> > +       int ret;
> > +
> > +       if (name) {
> > +               ret = device_property_match_string(dev, "io-backend-names",
> > +                                                  name);
> > +               if (ret < 0)
> > +                       return ERR_PTR(ret);
> > +               index = ret;
> > +       } else {
> > +               index = 0;
> > +       }
> > +
> > +       fwnode = fwnode_find_reference(dev_fwnode(dev), "io-backends", index);
> > +       if (IS_ERR(fwnode)) {
> > +               dev_err_probe(dev, PTR_ERR(fwnode),
> > +                             "Cannot get Firmware reference\n");
> > +               return ERR_CAST(fwnode);
> > +       }
> > +
> > +       guard(mutex)(&iio_back_lock);
> > +       list_for_each_entry(back, &iio_back_list, entry) {
> > +               if (!device_match_fwnode(back->dev, fwnode))
> > +                       continue;  
> 
> > +               fwnode_handle_put(fwnode);
> > +               ret = __devm_iio_backend_get(dev, back);  
> 
> This order makes me think about the reference counting. So, fwnode is
> the one of the backend devices to which the property points to.
> Another piece is the local (to this framework) list that keeps backend
> devices. So, fwnode reference can be  dropped earlier, while the usual
> pattern to interleave gets and puts in a chain. Dunno if above needs a
> comment, reordering or nothing.
> 
I'm lost. Why don't we need to hold fwnode reference for the
device_match_fwnode() just before here?

Or do you mean that we are safe here with the fwnode_handle_put() being
before the __devm_iio_backend_get()? I think you are correct that the
lifetimes are fine as we switched from the fwnode to the
iio_backend from the list at this point.

> > +               if (ret)
> > +                       return ERR_PTR(ret);
> > +
> > +               return back;
> > +       }
> > +
> > +       fwnode_handle_put(fwnode);
> > +       return ERR_PTR(-EPROBE_DEFER);  
> 
> While thinking about the above, I noticed the room to refactor.
> 
>   list_for_each_entry(...) {
>     if (...)
>       break;
>   }
>   fwnode_handle_put(...);
>   // Yes, we may use the below macro as the (global) pointers are
> protected by a mutex.
>   if (list_entry_is_head(...))

Knowing that means we failed to match is a bit obscure.

>     return ERR_PTR(...);
> 
>   ret = __devm_iio_backend_get(...);
>   ...

Maybe - it's a little ugly either way.  I don't think we care about
potentially holding the fwnode handle too long, so flipping over to
the cleanup.h handling (I need to get back to that sometime this week)
will make this all simpler.

> 
> > +}  
> 

Re: [PATCH v10 5/7] iio: add the IIO backend framework

[Andy Shevchenko]

On Sat, Feb 10, 2024 at 6:42 PM Jonathan Cameron <jic23@kernel.org> wrote:
> On Fri, 9 Feb 2024 18:30:53 +0200
> Andy Shevchenko <andy.shevchenko@gmail.com> wrote:
> > On Fri, Feb 9, 2024 at 5:26 PM Nuno Sa <nuno.sa@analog.com> wrote:

...

> > > +struct iio_backend *devm_iio_backend_get(struct device *dev, const char *name)
> > > +{
> > > +       struct fwnode_handle *fwnode;
> > > +       struct iio_backend *back;
> > > +       unsigned int index;
> > > +       int ret;
> > > +
> > > +       if (name) {
> > > +               ret = device_property_match_string(dev, "io-backend-names",
> > > +                                                  name);
> > > +               if (ret < 0)
> > > +                       return ERR_PTR(ret);
> > > +               index = ret;
> > > +       } else {
> > > +               index = 0;
> > > +       }
> > > +
> > > +       fwnode = fwnode_find_reference(dev_fwnode(dev), "io-backends", index);
> > > +       if (IS_ERR(fwnode)) {
> > > +               dev_err_probe(dev, PTR_ERR(fwnode),
> > > +                             "Cannot get Firmware reference\n");
> > > +               return ERR_CAST(fwnode);
> > > +       }
> > > +
> > > +       guard(mutex)(&iio_back_lock);
> > > +       list_for_each_entry(back, &iio_back_list, entry) {
> > > +               if (!device_match_fwnode(back->dev, fwnode))
> > > +                       continue;
> >
> > > +               fwnode_handle_put(fwnode);
> > > +               ret = __devm_iio_backend_get(dev, back);
> >
> > This order makes me think about the reference counting. So, fwnode is
> > the one of the backend devices to which the property points to.
> > Another piece is the local (to this framework) list that keeps backend
> > devices. So, fwnode reference can be  dropped earlier, while the usual
> > pattern to interleave gets and puts in a chain. Dunno if above needs a
> > comment, reordering or nothing.
> >
> I'm lost. Why don't we need to hold fwnode reference for the
> device_match_fwnode() just before here?

> Or do you mean that we are safe here with the fwnode_handle_put() being
> before the __devm_iio_backend_get()?

This one.

> I think you are correct that the
> lifetimes are fine as we switched from the fwnode to the
> iio_backend from the list at this point.
>
> > > +               if (ret)
> > > +                       return ERR_PTR(ret);
> > > +
> > > +               return back;
> > > +       }
> > > +
> > > +       fwnode_handle_put(fwnode);
> > > +       return ERR_PTR(-EPROBE_DEFER);
> >
> > While thinking about the above, I noticed the room to refactor.
> >
> >   list_for_each_entry(...) {
> >     if (...)
> >       break;
> >   }
> >   fwnode_handle_put(...);
> >   // Yes, we may use the below macro as the (global) pointers are
> > protected by a mutex.
> >   if (list_entry_is_head(...))
>
> Knowing that means we failed to match is a bit obscure.
>
> >     return ERR_PTR(...);
> >
> >   ret = __devm_iio_backend_get(...);
> >   ...
>
> Maybe - it's a little ugly either way.  I don't think we care about
> potentially holding the fwnode handle too long, so flipping over to
> the cleanup.h handling (I need to get back to that sometime this week)
> will make this all simpler.

Yes, I agree with your point of view. That's why I'm not insisting on
this change.

> > > +}


-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v10 7/7] iio: adc: adi-axi-adc: move to backend framework

[Nuno Sá]

On Fri, 2024-02-09 at 18:45 +0200, Andy Shevchenko wrote:
> On Fri, Feb 9, 2024 at 5:26 PM Nuno Sa <nuno.sa@analog.com> wrote:
> > 
> > Move to the IIO backend framework. Devices supported by adi-axi-adc now
> > register themselves as backend devices.
> 
> ...
> 
> > -#include <linux/iio/iio.h>
> > -#include <linux/iio/sysfs.h>
> > -#include <linux/iio/buffer.h>
> > -#include <linux/iio/buffer-dmaengine.h>
> > -
> >  #include <linux/fpga/adi-axi-common.h>
> > -#include <linux/iio/adc/adi-axi-adc.h>
> 
> + Blank line?
> 

can be...

> > +#include <linux/iio/backend.h>
> > +#include <linux/iio/buffer-dmaengine.h>
> > +#include <linux/iio/buffer.h>
> > +#include <linux/iio/iio.h>
> 
> ...
> 
> > +static int axi_adc_enable(struct iio_backend *back)
> >  {
> > +       struct adi_axi_adc_state *st = iio_backend_get_priv(back);
> >         int ret;
> > 
> > +       ret = regmap_set_bits(st->regmap, ADI_AXI_REG_RSTN,
> > +                             ADI_AXI_REG_RSTN_MMCM_RSTN);
> > +       if (ret)
> > +               return ret;
> 
> > +       fsleep(10);
> 
> Would be nice to have a comment that probably the datasheet defines
> the minimum timeout for reset. Ah and you decreased it 1000x times,
> why?
> 

Arghh, always forget that fsleep() is us... That said, there's no minimum timeout
specified in the docs. I guess the original developer has the sleeps out of habit or
some "hidden" knowledge. In my testing I did not noticed anything weird with the
10us. I'll move back to the original timeout though. I can then check and make sure
10us is enough and send a follow up patch.

> > +       return regmap_set_bits(st->regmap, ADI_AXI_REG_RSTN,
> > +                              ADI_AXI_REG_RSTN_RSTN |
> > ADI_AXI_REG_RSTN_MMCM_RSTN);
> >  }
> 
> ...
> 
> > +       expected_ver = (unsigned int *)device_get_match_data(&pdev->dev);
> 
> expected_ver should have const and you can drop the casting IIUC.

Right...

> 
> > +       if (!expected_ver)
> > +               return -ENODEV;
> 

Re: [PATCH v10 6/7] iio: adc: ad9467: convert to backend framework

[Nuno Sá]

On Fri, 2024-02-09 at 18:37 +0200, Andy Shevchenko wrote:
> On Fri, Feb 9, 2024 at 5:26 PM Nuno Sa <nuno.sa@analog.com> wrote:
> > 
> > Convert the driver to use the new IIO backend framework. The device
> > functionality is expected to be the same (meaning no added or removed
> > features).
> > 
> > Also note this patch effectively breaks ABI and that's needed so we can
> > properly support this device and add needed features making use of the
> > new IIO framework.
> > 
> > Given the lack of features (and devices supported) in the ad9467 driver
> > compared with the ADI out of tree version, we don't expect any user of
> > the upstream driver so no one should notice the ABI breakage. However,
> > if someone is affected by this, ADI will happily support transitioning
> > to the backend framework.
> 
> ...
> 
> >  struct ad9467_chip_info {
> > -       struct adi_axi_adc_chip_info    axi_adc_info;
> > -       unsigned int                    default_output_mode;
> > -       unsigned int                    vref_mask;
> > +       const char              *name;
> > +       unsigned int            id;
> > +       const struct            iio_chan_spec *channels;
> > +       unsigned int            num_channels;
> > +       const unsigned int      (*scale_table)[2];
> > +       int                     num_scales;
> > +       unsigned long           max_rate;
> > +       unsigned int            default_output_mode;
> > +       unsigned int            vref_mask;
> >  };
> 
> Seems like you haven't checked this layout with `pahole`.
> 

Not really... IIRC, I just copied the members as-is from the previous struct. Can be
done later I guess...

> ...
> 
> > +static int ad9467_iio_backend_get(struct ad9467_state *st)
> > +{
> > +       struct device *dev = &st->spi->dev;
> > +       struct device_node *__back;
> > +
> > +       st->back = devm_iio_backend_get(&st->spi->dev, NULL);
> 
> Simply 'dev' as the first parameter?
> 

Makes sense...

> ...
> 
> > +       /* If not found, don't error out as we might have legacy DT property */
> 
> This seems related to ENOENT, correct?

Yeah, the comments are in line with the original version of the code where I was
first checking for errors.

- Nuno Sá