Re: [PATCH v2 4/7] drivers/base: Add interface framework

[Daniel Vetter]

On Tue, May 13, 2014 at 05:30:47PM +0200, Thierry Reding wrote:
> From: Thierry Reding <treding@xxxxxxxxxx>
> 
> Some drivers, such as graphics drivers in the DRM subsystem, do not have
> a real device that they can bind to. They are often composed of several
> devices, each having their own driver. The master/component framework
> can be used in these situations to collect the devices pertaining to one
> logical device, wait until all of them have registered and then bind
> them all at once.
> 
> For some situations this is only a partial solution. An implementation
> of a master still needs to be registered with the system somehow. Many
> drivers currently resort to creating a dummy device that a driver can
> bind to and register the master against. This is problematic since it
> requires (and presumes) knowledge about the system within drivers.
> 
> Furthermore there are setups where a suitable device already exists, but
> is already bound to a driver. For example, on Tegra the following device
> tree extract (simplified) represents the host1x device along with child
> devices:
> 
> 	host1x {
> 		display-controller {
> 			...
> 		};
> 
> 		display-controller {
> 			...
> 		};
> 
> 		hdmi {
> 			...
> 		};
> 
> 		dsi {
> 			...
> 		};
> 
> 		csi {
> 			...
> 		};
> 
> 		video-input {
> 			...
> 		};
> 	};
> 
> Each of the child devices is in turn a client of host1x, in that it can
> request resources (command stream DMA channels and syncpoints) from it.
> To implement the DMA channel and syncpoint infrastructure, host1x comes
> with its own driver. Children are implemented in separate drivers. In
> Linux this set of devices would be exposed by DRM and V4L2 drivers.
> 
> However, neither the DRM nor the V4L2 drivers have a single device that
> they can bind to. The DRM device is composed of the display controllers
> and the various output devices, whereas the V4L2 device is composed of
> one or more video input devices.
> 
> This patch introduces the concept of an interface and drivers that can
> bind to a given interface. An interface can be exposed by any device,
> and interface drivers can bind to these interfaces. Multiple drivers can
> bind against a single interface. When a device is removed, interfaces
> exposed by it will be removed as well, thereby removing the drivers that
> were bound to those interfaces.
> 
> In the example above, the host1x device would expose the "tegra-host1x"
> interface. DRM and V4L2 drivers can then bind to that interface and
> instantiate the respective subsystem objects from there.
> 
> Signed-off-by: Thierry Reding <treding@xxxxxxxxxx>
> ---
> Note that I'd like to merge this through the Tegra DRM tree so that the
> changes to the Tegra DRM driver later in this series can be merged at
> the same time and are not delayed for another release cycle.
> 
> In particular that means that I'm looking for an Acked-by from Greg.
> 
>  drivers/base/Makefile     |   2 +-
>  drivers/base/interface.c  | 186 ++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/interface.h |  40 ++++++++++
>  3 files changed, 227 insertions(+), 1 deletion(-)
>  create mode 100644 drivers/base/interface.c
>  create mode 100644 include/linux/interface.h

Hm, this interface stuff smells like bus drivers light. Should we instead
have a pile of helpers to make creating new buses with match methods more
trivial? There's a fairly big pile of small use-cases where this might be
useful. In your case here all the host1x children would sit on a host1x
bus. Admittedly I didn't look into the details.
-Daniel

> 
> diff --git a/drivers/base/Makefile b/drivers/base/Makefile
> index 04b314e0fa51..b5278904e443 100644
> --- a/drivers/base/Makefile
> +++ b/drivers/base/Makefile
> @@ -4,7 +4,7 @@ obj-y			:= component.o core.o bus.o dd.o syscore.o \
>  			   driver.o class.o platform.o \
>  			   cpu.o firmware.o init.o map.o devres.o \
>  			   attribute_container.o transport_class.o \
> -			   topology.o container.o
> +			   topology.o container.o interface.o
>  obj-$(CONFIG_DEVTMPFS)	+= devtmpfs.o
>  obj-$(CONFIG_DMA_CMA) += dma-contiguous.o
>  obj-y			+= power/
> diff --git a/drivers/base/interface.c b/drivers/base/interface.c
> new file mode 100644
> index 000000000000..411f6cdf90e7
> --- /dev/null
> +++ b/drivers/base/interface.c
> @@ -0,0 +1,186 @@
> +/*
> + * Copyright (C) 2014 NVIDIA Corporation. All rights reserved.
> + *
> + * 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.
> + */
> +
> +#define pr_fmt(fmt) "interface: " fmt
> +
> +#include <linux/device.h>
> +#include <linux/interface.h>
> +#include <linux/mutex.h>
> +#include <linux/slab.h>
> +
> +static DEFINE_MUTEX(interfaces_lock);
> +static LIST_HEAD(interfaces);
> +static LIST_HEAD(drivers);
> +
> +struct interface_attachment {
> +	struct interface_driver *driver;
> +	struct list_head list;
> +};
> +
> +static bool interface_match(struct interface *intf,
> +			    struct interface_driver *driver)
> +{
> +	return strcmp(intf->name, driver->name) == 0;
> +}
> +
> +static bool interface_attached(struct interface *intf,
> +			       struct interface_driver *driver)
> +{
> +	struct interface_attachment *attach;
> +
> +	list_for_each_entry(attach, &intf->drivers, list)
> +		if (attach->driver == driver)
> +			return true;
> +
> +	return false;
> +}
> +
> +static int interface_attach(struct interface *intf,
> +			    struct interface_driver *driver)
> +{
> +	struct interface_attachment *attach;
> +
> +	attach = kzalloc(sizeof(*attach), GFP_KERNEL);
> +	if (!attach)
> +		return -ENOMEM;
> +
> +	INIT_LIST_HEAD(&attach->list);
> +	attach->driver = driver;
> +
> +	list_add_tail(&attach->list, &intf->drivers);
> +
> +	return 0;
> +}
> +
> +static void interface_detach(struct interface *intf,
> +			     struct interface_driver *driver)
> +{
> +	struct interface_attachment *attach;
> +
> +	list_for_each_entry(attach, &intf->drivers, list) {
> +		if (attach->driver == driver) {
> +			list_del(&attach->list);
> +			kfree(attach);
> +			return;
> +		}
> +	}
> +}
> +
> +static void interface_bind(struct interface *intf,
> +			   struct interface_driver *driver)
> +{
> +	int err;
> +
> +	if (interface_attached(intf, driver))
> +		return;
> +
> +	if (!interface_match(intf, driver))
> +		return;
> +
> +	err = interface_attach(intf, driver);
> +	if (err < 0) {
> +		pr_err("failed to attach driver %ps to interface %s: %d\n",
> +		       driver, intf->name, err);
> +		return;
> +	}
> +
> +	err = driver->bind(intf);
> +	if (err < 0) {
> +		pr_err("failed to bind driver %ps to interface %s: %d\n",
> +		       driver, intf->name, err);
> +		interface_detach(intf, driver);
> +		return;
> +	}
> +
> +	pr_debug("driver %ps bound to interface %s\n", driver, intf->name);
> +}
> +
> +static void interface_unbind(struct interface *intf,
> +			     struct interface_driver *driver)
> +{
> +	if (!interface_attached(intf, driver))
> +		return;
> +
> +	interface_detach(intf, driver);
> +	driver->unbind(intf);
> +
> +	pr_debug("driver %ps unbound from interface %s\n", driver, intf->name);
> +}
> +
> +int interface_add(struct interface *intf)
> +{
> +	struct interface_driver *driver;
> +
> +	INIT_LIST_HEAD(&intf->drivers);
> +	INIT_LIST_HEAD(&intf->list);
> +
> +	mutex_lock(&interfaces_lock);
> +
> +	list_add_tail(&intf->list, &interfaces);
> +
> +	pr_debug("interface %s added for device %s\n", intf->name,
> +		 dev_name(intf->dev));
> +
> +	list_for_each_entry(driver, &drivers, list)
> +		interface_bind(intf, driver);
> +
> +	mutex_unlock(&interfaces_lock);
> +
> +	return 0;
> +}
> +
> +void interface_remove(struct interface *intf)
> +{
> +	struct interface_driver *driver;
> +
> +	mutex_lock(&interfaces_lock);
> +
> +	list_for_each_entry(driver, &drivers, list)
> +		interface_unbind(intf, driver);
> +
> +	list_del_init(&intf->list);
> +
> +	pr_debug("interface %s removed for device %s\n", intf->name,
> +		 dev_name(intf->dev));
> +
> +	mutex_unlock(&interfaces_lock);
> +}
> +
> +int interface_register_driver(struct interface_driver *driver)
> +{
> +	struct interface *intf;
> +
> +	mutex_lock(&interfaces_lock);
> +
> +	list_add_tail(&driver->list, &drivers);
> +
> +	pr_debug("driver %ps added\n", driver);
> +
> +	list_for_each_entry(intf, &interfaces, list)
> +		interface_bind(intf, driver);
> +
> +	mutex_unlock(&interfaces_lock);
> +
> +	return 0;
> +}
> +
> +void interface_unregister_driver(struct interface_driver *driver)
> +{
> +	struct interface *intf;
> +
> +	mutex_lock(&interfaces_lock);
> +
> +	list_for_each_entry(intf, &interfaces, list)
> +		interface_unbind(intf, driver);
> +
> +	list_del_init(&driver->list);
> +
> +	pr_debug("driver %ps removed\n", driver);
> +
> +	mutex_unlock(&interfaces_lock);
> +}
> diff --git a/include/linux/interface.h b/include/linux/interface.h
> new file mode 100644
> index 000000000000..2c49ad3912fe
> --- /dev/null
> +++ b/include/linux/interface.h
> @@ -0,0 +1,40 @@
> +/*
> + * Copyright (C) 2014 NVIDIA Corporation. All rights reserved.
> + *
> + * 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 INTERFACE_H
> +#define INTERFACE_H
> +
> +#include <linux/list.h>
> +
> +struct device;
> +struct interface;
> +
> +struct interface_driver {
> +	const char *name;
> +
> +	int (*bind)(struct interface *intf);
> +	void (*unbind)(struct interface *intf);
> +
> +	struct list_head list;
> +};
> +
> +int interface_register_driver(struct interface_driver *driver);
> +void interface_unregister_driver(struct interface_driver *driver);
> +
> +struct interface {
> +	const char *name;
> +	struct device *dev;
> +
> +	struct list_head drivers;
> +	struct list_head list;
> +};
> +
> +int interface_add(struct interface *intf);
> +void interface_remove(struct interface *intf);
> +
> +#endif
> -- 
> 1.9.2
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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