Hi Guennadi,

On Tuesday 08 January 2013 10:25:15 Guennadi Liakhovetski wrote:

On Tue, 8 Jan 2013, Laurent Pinchart wrote:

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On Monday 07 January 2013 11:23:55 Guennadi Liakhovetski wrote:

quoted

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From 0e1eae338ba898dc25ec60e3dba99e5581edc199 Mon Sep 17 00:00:00 2001

From: Guennadi Liakhovetski <redacted>
Date: Fri, 19 Oct 2012 23:40:44 +0200
Subject: [PATCH] media: V4L2: support asynchronous subdevice
registration

Currently bridge device drivers register devices for all subdevices
synchronously, tupically, during their probing. E.g. if an I2C CMOS
sensor is attached to a video bridge device, the bridge driver will
create an I2C device and wait for the respective I2C driver to probe.
This makes linking of devices straight forward, but this approach cannot
be used with intrinsically asynchronous and unordered device
registration systems like the Flattened Device Tree. To support such
systems this patch adds an asynchronous subdevice registration framework
to V4L2. To use it respective (e.g. I2C) subdevice drivers must request
deferred probing as long as their bridge driver hasn't probed. The
bridge driver during its probing submits a an arbitrary number of
subdevice descriptor groups to the framework to manage. After that it
can add callbacks to each of those groups to be called at various stages
during subdevice probing, e.g. after completion. Then the bridge driver
can request single groups to be probed, finish its own probing and
continue its video subsystem configuration from its callbacks.

Signed-off-by: Guennadi Liakhovetski <redacted>
---

v4: Fixed v4l2_async_notifier_register() for the case, when subdevices
probe successfully before the bridge, thanks to Prabhakar for reporting

 drivers/media/v4l2-core/Makefile     |    3 +-
 drivers/media/v4l2-core/v4l2-async.c |  284 +++++++++++++++++++++++++++
 include/media/v4l2-async.h           |  113 ++++++++++++++
 3 files changed, 399 insertions(+), 1 deletions(-)
 create mode 100644 drivers/media/v4l2-core/v4l2-async.c
 create mode 100644 include/media/v4l2-async.h

[snip]

quoted

diff --git a/include/media/v4l2-async.h b/include/media/v4l2-async.h
new file mode 100644
index 0000000..91d436d
--- /dev/null
+++ b/include/media/v4l2-async.h

@@ -0,0 +1,113 @@
+/*
+ * V4L2 asynchronous subdevice registration API
+ *
+ * Copyright (C) 2012, Guennadi Liakhovetski <g.liakhovetski@gmx.de>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#ifndef V4L2_ASYNC_H
+#define V4L2_ASYNC_H
+
+#include <linux/list.h>
+#include <linux/mutex.h>
+#include <linux/notifier.h>
+
+#include <media/v4l2-subdev.h>
+
+struct device;
+struct v4l2_device;
+struct v4l2_async_notifier;
+
+enum v4l2_async_bus_type {
+	V4L2_ASYNC_BUS_SPECIAL,
+	V4L2_ASYNC_BUS_PLATFORM,
+	V4L2_ASYNC_BUS_I2C,
+};
+
+struct v4l2_async_hw_device {
+	enum v4l2_async_bus_type bus_type;
+	union {
+		struct {
+			const char *name;
+		} platform;
+		struct {
+			int adapter_id;
+			unsigned short address;
+		} i2c;
+		struct {
+			bool (*match)(struct device *,
+				      struct v4l2_async_hw_device *);
+			void *priv;
+		} special;
+	} match;
+};
+
+/**
+ * struct v4l2_async_subdev - sub-device descriptor, as known to a

bridge
+ * @hw:		this device descriptor
+ * @list:	member in a list of subdevices
+ */
+struct v4l2_async_subdev {
+	struct v4l2_async_hw_device hw;
+	struct list_head list;
+};
+
+/**
+ * v4l2_async_subdev_list - provided by subdevices
+ * @list:	member in a list of subdevices
+ * @dev:	hardware device
+ * @subdev:	V4L2 subdevice
+ * @asd:	pointer to respective struct v4l2_async_subdev
+ * @notifier:	pointer to managing notifier
+ */
+struct v4l2_async_subdev_list {
+	struct list_head list;
+	struct device *dev;
+	struct v4l2_subdev *subdev;
+	struct v4l2_async_subdev *asd;
+	struct v4l2_async_notifier *notifier;
+};
+
+/**
+ * v4l2_async_notifier - provided by bridges
+ * @subdev_num:	number of subdevices
+ * @subdev:	array of pointers to subdevices
+ * @v4l2_dev:	pointer to sruct v4l2_device
+ * @waiting:	list of subdevices, waiting for their drivers
+ * @done:	list of subdevices, already probed
+ * @list:	member in a global list of notifiers
+ * @bind:	a subdevice driver is about to probe one of your subdevices
+ * @bound:	a subdevice driver has successfully probed one of your
subdevices + * @complete:	all your subdevices have been probed
successfully
+ * @unbind:	a subdevice is leaving
+ */
+struct v4l2_async_notifier {
+	int subdev_num;
+	struct v4l2_async_subdev **subdev;
+	struct v4l2_device *v4l2_dev;
+	struct list_head waiting;
+	struct list_head done;
+	struct list_head list;
+	int (*bind)(struct v4l2_async_notifier *notifier,
+		    struct v4l2_async_subdev_list *asdl);
+	int (*bound)(struct v4l2_async_notifier *notifier,
+		     struct v4l2_async_subdev_list *asdl);
+	int (*complete)(struct v4l2_async_notifier *notifier);
+	void (*unbind)(struct v4l2_async_notifier *notifier,
+		       struct v4l2_async_subdev_list *asdl);
+};
+
+int v4l2_async_notifier_register(struct v4l2_device *v4l2_dev,
+				 struct v4l2_async_notifier *notifier);
+void v4l2_async_notifier_unregister(struct v4l2_async_notifier
*notifier);
+/*
+ * If subdevice probing fails any time after v4l2_async_subdev_bind(),
no
+ * clean up must be called. This function is only a message of
intention.
+ */
+int v4l2_async_subdev_bind(struct v4l2_async_subdev_list *asdl);
+int v4l2_async_subdev_bound(struct v4l2_async_subdev_list *asdl);

Could you please explain why you need both a bind notifier and a bound
notifier ? I was expecting a single v4l2_async_subdev_register() call in
subdev drivers (and, thinking about it, I would probably name it
v4l2_subdev_register()).

I think I can, yes. Because between .bind() and .bound() the subdevice
driver does the actual hardware probing. So, .bind() is used to make sure
the hardware can be accessed, most importantly to provide a clock to the
subdevice. You can look at soc_camera_async_bind(). There I'm registering
the clock for the subdevice, about to bind. Why I cannot do it before, is
because I need subdevice name for clock matching. With I2C subdevices the
subdevice name contains the name of the driver, adapter number and i2c
address. The latter 2 I've got from host subdevice list. But not the
driver name. I thought about also passing the driver name there, but that
seemed too limiting to me. I also request regulators there, because before
->bound() the sensor driver, but that could be done on the first call to
soc_camera_power_on(), although doing this "first call" thingie is kind of
hackish too. I could add one more soc-camera-power helper like
soc_camera_prepare() or similar too.

I think a soc_camera_power_init() function (or similar) would be a good idea, 
yes.

So, the main problem is the clock
subdevice name. Also see the comment in soc_camera.c:

	/*
	 * It is ok to keep the clock for the whole soc_camera_device life-time,
	 * in principle it would be more logical to register the clock on icd
	 * creation, the only problem is, that at that time we don't know the
	 * driver name yet.
	 */

I think we should fix that problem instead of shaping the async API around a 
workaround :-)

From the subdevice point of view, the probe function should request resources, 

perform whatever initialization is needed (including verifying that the 
hardware is functional when possible), and the register the subdev with the 
code if everything succeeded. Splitting registration into bind() and bound() 
appears a bit as a workaround to me.

If we need a workaround, I'd rather pass the device name in addition to the 
I2C adapter number and address, instead of embedding the workaround in this 
new API.

quoted

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+void v4l2_async_subdev_unbind(struct v4l2_async_subdev_list *asdl);
+#endif

-- 
Regards,

Laurent Pinchart