Merge tag 'driver-core-3.14-rc1' of... (d3bad75a) · Commits · e / devices / android_kernel_teracube_2e

Documentation/driver-model/design-patterns.txt

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		Device Driver Design Patterns
		~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

		This document describes a few common design patterns found in device drivers.
		It is likely that subsystem maintainers will ask driver developers to
		conform to these design patterns.

		1. State Container
		2. container_of()


		1. State Container
		~~~~~~~~~~~~~~~~~~

		While the kernel contains a few device drivers that assume that they will
		only be probed() once on a certain system (singletons), it is custom to assume
		that the device the driver binds to will appear in several instances. This
		means that the probe() function and all callbacks need to be reentrant.

		The most common way to achieve this is to use the state container design
		pattern. It usually has this form:

		struct foo {
		spinlock_t lock; /* Example member */
		(...)
		};

		static int foo_probe(...)
		{
		struct foo *foo;

		foo = devm_kzalloc(dev, sizeof(*foo), GFP_KERNEL);
		if (!foo)
		return -ENOMEM;
		spin_lock_init(&foo->lock);
		(...)
		}

		This will create an instance of struct foo in memory every time probe() is
		called. This is our state container for this instance of the device driver.
		Of course it is then necessary to always pass this instance of the
		state around to all functions that need access to the state and its members.

		For example, if the driver is registering an interrupt handler, you would
		pass around a pointer to struct foo like this:

		static irqreturn_t foo_handler(int irq, void *arg)
		{
		struct foo *foo = arg;
		(...)
		}

		static int foo_probe(...)
		{
		struct foo *foo;

		(...)
		ret = request_irq(irq, foo_handler, 0, "foo", foo);
		}

		This way you always get a pointer back to the correct instance of foo in
		your interrupt handler.


		2. container_of()
		~~~~~~~~~~~~~~~~~

		Continuing on the above example we add an offloaded work:

		struct foo {
		spinlock_t lock;
		struct workqueue_struct *wq;
		struct work_struct offload;
		(...)
		};

		static void foo_work(struct work_struct *work)
		{
		struct foo *foo = container_of(work, struct foo, offload);

		(...)
		}

		static irqreturn_t foo_handler(int irq, void *arg)
		{
		struct foo *foo = arg;

		queue_work(foo->wq, &foo->offload);
		(...)
		}

		static int foo_probe(...)
		{
		struct foo *foo;

		foo->wq = create_singlethread_workqueue("foo-wq");
		INIT_WORK(&foo->offload, foo_work);
		(...)
		}

		The design pattern is the same for an hrtimer or something similar that will
		return a single argument which is a pointer to a struct member in the
		callback.

		container_of() is a macro defined in <linux/kernel.h>

		What container_of() does is to obtain a pointer to the containing struct from
		a pointer to a member by a simple subtraction using the offsetof() macro from
		standard C, which allows something similar to object oriented behaviours.
		Notice that the contained member must not be a pointer, but an actual member
		for this to work.

		We can see here that we avoid having global pointers to our struct foo *
		instance this way, while still keeping the number of parameters passed to the
		work function to a single pointer.

Documentation/kobject.txt

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		@@ -342,7 +342,10 @@ kset use:

		When you are finished with the kset, call:
		void kset_unregister(struct kset *kset);
		to destroy it.
		to destroy it. This removes the kset from sysfs and decrements its reference
		count. When the reference count goes to zero, the kset will be released.
		Because other references to the kset may still exist, the release may happen
		after kset_unregister() returns.

		An example of using a kset can be seen in the
		samples/kobject/kset-example.c file in the kernel tree.

arch/x86/kernel/cpu/microcode/amd.c

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		@@ -433,7 +433,7 @@ static enum ucode_state request_microcode_amd(int cpu, struct device *device,
		if (c->x86 >= 0x15)
		snprintf(fw_name, sizeof(fw_name), "amd-ucode/microcode_amd_fam%.2xh.bin", c->x86);

		if (request_firmware(&fw, (const char *)fw_name, device)) {
		if (request_firmware_direct(&fw, (const char *)fw_name, device)) {
		pr_debug("failed to load file %s\n", fw_name);
		goto out;
		}

arch/x86/kernel/cpu/microcode/intel.c

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		@@ -278,7 +278,7 @@ static enum ucode_state request_microcode_fw(int cpu, struct device *device,
		sprintf(name, "intel-ucode/%02x-%02x-%02x",
		c->x86, c->x86_model, c->x86_mask);

		if (request_firmware(&firmware, name, device)) {
		if (request_firmware_direct(&firmware, name, device)) {
		pr_debug("data file %s load failed\n", name);
		return UCODE_NFOUND;
		}

drivers/base/Makefile

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		# Makefile for the Linux device tree

		obj-y := core.o bus.o dd.o syscore.o \
		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 \