Re: [RFC PATCH v2 2/4] Core device subsystem implementation

[Grant Likely]

On Fri, Jul 08, 2011 at 09:54:08AM +0100, Marc Zyngier wrote:
> There is a small number of devices that the core kernel needs very
> early in the boot process, namely an interrupt controller and a timer,
> long before the device model is up and running.
> 
> The "core device subsystem" offers a class based device/driver
> matching model, doesn't rely on any other subsystem, is very (too?)
> simple, and support getting information both from DT as well as from
> static data provided by the platform. It also gives the opportunity to
> define the probing order by offering a sorting hook at runtime.

I know you're trying to support platforms that probably won't be
converted to DT, but is that really worth the effort?  Those platforms
are already supported by the kernel, and so are not dependant on this
infrastructure.  New ARM platform support AFAIK now is required to use
DT.

For the DT case, I'm not convinced this is the right direction to go.
My (admittedly limited) understanding of this patch series is that it
purposefully stratifies different kinds of devices into an explicit
init order, while I think we need *less* stratification of device
initialization, and provide device drivers with the ability to sort
themselves.

That said, I do understand the issues your trying to solve to get a
core timer and the core irq controllers set up really early, without a
lot of code duplication.  I've been thinking about the same problem.
It is a very small set of devices that need to be set up this early.
I've been looking at it from the perspective of what can be done to
get things bootstrapped, but then hand off to real devices in the real
device model without an artificial separation between the two.

Regardless, I'll go through this patch set and give you my feedback,
and I'll try to keep my own biases in check as I do so....

> 
> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
> ---
>  arch/arm/kernel/vmlinux.lds.S     |    1 +
>  drivers/base/Makefile             |    3 +-
>  drivers/base/core_device.c        |  108 +++++++++++++++++++++++++++++++++++++
>  include/asm-generic/vmlinux.lds.h |    6 ++
>  include/linux/core_device.h       |   69 +++++++++++++++++++++++
>  5 files changed, 186 insertions(+), 1 deletions(-)
>  create mode 100644 drivers/base/core_device.c
>  create mode 100644 include/linux/core_device.h
> 
> diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
> index e5287f2..ae33310 100644
> --- a/arch/arm/kernel/vmlinux.lds.S
> +++ b/arch/arm/kernel/vmlinux.lds.S
> @@ -70,6 +70,7 @@ SECTIONS
>  
>  		INIT_SETUP(16)
>  
> +		INIT_CORE_DRV
>  		INIT_CALLS
>  		CON_INITCALL
>  		SECURITY_INITCALL
> diff --git a/drivers/base/Makefile b/drivers/base/Makefile
> index 4c5701c..79476f0 100644
> --- a/drivers/base/Makefile
> +++ b/drivers/base/Makefile
> @@ -3,7 +3,8 @@
>  obj-y			:= core.o sys.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
> +			   attribute_container.o transport_class.o \
> +			   core_device.o

Should this really be hard-enabled?  If a majority of platforms are
not using this, then it should be CONFIG'ed out.

>  obj-$(CONFIG_DEVTMPFS)	+= devtmpfs.o
>  obj-y			+= power/
>  obj-$(CONFIG_HAS_DMA)	+= dma-mapping.o
> diff --git a/drivers/base/core_device.c b/drivers/base/core_device.c
> new file mode 100644
> index 0000000..9262145
> --- /dev/null
> +++ b/drivers/base/core_device.c
> @@ -0,0 +1,108 @@
> +/*
> + * Copyright (C) 2011 ARM Ltd
> + * Written by Marc Zyngier <marc.zyngier@xxxxxxx>
> + *
> + * 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.
> + *
> + * Core device init support
> + */
> +#include <linux/core_device.h>
> +#include <linux/of_platform.h>
> +#include <linux/slab.h>
> +
> +static struct list_head anchors[CORE_DEV_CLASS_MAX] __initdata = {
> +	[CORE_DEV_CLASS_IRQ]   = LIST_HEAD_INIT(anchors[CORE_DEV_CLASS_IRQ]),
> +	[CORE_DEV_CLASS_TIMER] = LIST_HEAD_INIT(anchors[CORE_DEV_CLASS_TIMER]),
> +};
> +
> +static int __init core_device_match(struct core_device *dev,
> +				    struct core_device_id *ids)
> +{
> +	int i;
> +#ifdef CONFIG_OF
> +	if (dev->of_node)
> +		for (i = 0; ids[i].name != NULL; i++)
> +			if (of_device_is_compatible(dev->of_node,
> +						    ids[i].name))
> +				return 1;
> +#endif
> +	for (i = 0; ids[i].name != NULL; i++)
> +		if (!strcmp(dev->name, ids[i].name))
> +			return 1;
> +
> +	return 0;
> +}
> +
> +void __init core_device_register(enum core_device_class class,
> +			  struct core_device *dev)
> +{
> +	list_add_tail(&dev->entry, &anchors[class]);
> +}
> +
> +extern const struct core_driver_setup_block __core_driver_block_start[],
> +					    __core_driver_block_end[];
> +
> +void __init core_driver_init_class(enum core_device_class class,
> +				   void (*sort)(struct list_head *))
> +{
> +	const struct core_driver_setup_block *b;
> +	struct core_device *dev, *tmp;
> +	int err;
> +
> +	if (sort)
> +		sort(&anchors[class]);
> +
> +	list_for_each_entry_safe(dev, tmp, &anchors[class], entry) {
> +		pr_debug("core: matching device %s(%d)\n", dev->name, class);
> +		for (b = __core_driver_block_start;
> +		     b < __core_driver_block_end;
> +		     b++) {
> +			if (b->class != class ||
> +			    !core_device_match(dev, b->drv->ids))
> +				continue;
> +			
> +			pr_debug("core: matched device %s\n", dev->name);
> +			err = b->drv->init(dev);
> +			if (err)
> +				pr_warning("core: %s init failed\n", dev->name);
> +		}
> +
> +		list_del(&dev->entry);
> +#ifdef CONFIG_OF
> +		if (dev->of_node) { /* These are dynamically allocated */
> +			kfree(dev->resource);
> +			kfree(dev);
> +		}
> +#endif
> +	}
> +}

I think Greg commented on this, but I'll say the same thing.  I don't
think it is a good idea to try and classify core devices.  If it is
needed, there should be only one level of core devices, and they
should have the ability to sort themselves into the correct init
order.

> +
> +#ifdef CONFIG_OF
> +void __init of_core_device_populate(enum core_device_class class,
> +			     struct of_device_id *matches)
> +{
> +	struct device_node *np;
> +	struct core_device *dev;
> +	int num_res;
> +
> +	for_each_matching_node(np, matches) {
> +		pr_debug("core: registering OF device %s\n", np->full_name);
> +		dev = kzalloc(sizeof(*dev), GFP_KERNEL);
> +		if (!dev)
> +			return;
> +		dev->name = np->name;
> +		dev->of_node = np;
> +
> +		dev->resource = of_device_alloc_resources(np, &num_res);
> +		if (num_res < 0) {
> +			kfree(dev);
> +			return;
> +		}
> +		dev->num_resources = num_res;
> +
> +		core_device_register(class, dev);
> +	}
> +}
> +#endif

I'm concerned here about how a platform decides which devices are
'core' and which are not.  It doesn't make sense to have a
"core-device" compatible value or similar because it doesn't actually
describe the hardware requirements.  It only describes how the current
Linux kernel wants to initialize the world, and that is something very
much subject to change.

Also, for any device nodes picked up by this function, the driver
model would also need to inhibit those same nodes from being picked up
by of_platform_populate(), otherwise it could end up with two drivers
bound to the same device.  How are you thinking about handling it?

g.

> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index db22d13..2b1590a 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -616,6 +616,11 @@
>  		*(.init.setup)						\
>  		VMLINUX_SYMBOL(__setup_end) = .;
>  
> +#define INIT_CORE_DRV							\
> +		VMLINUX_SYMBOL(__core_driver_block_start) = .;		\
> +		*(.init.core_driver)					\
> +		VMLINUX_SYMBOL(__core_driver_block_end) = .;
> +
>  #define INITCALLS							\
>  	*(.initcallearly.init)						\
>  	VMLINUX_SYMBOL(__early_initcall_end) = .;			\
> @@ -797,6 +802,7 @@
>  	.init.data : AT(ADDR(.init.data) - LOAD_OFFSET) {		\
>  		INIT_DATA						\
>  		INIT_SETUP(initsetup_align)				\
> +		INIT_CORE_DRV						\
>  		INIT_CALLS						\
>  		CON_INITCALL						\
>  		SECURITY_INITCALL					\
> diff --git a/include/linux/core_device.h b/include/linux/core_device.h
> new file mode 100644
> index 0000000..ca67e5e
> --- /dev/null
> +++ b/include/linux/core_device.h
> @@ -0,0 +1,69 @@
> +/*
> + * Copyright (C) 2011 ARM Ltd
> + * Written by Marc Zyngier <marc.zyngier@xxxxxxx>
> + *
> + * 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.
> + *
> + * Core device init support
> + */
> +
> +#ifndef _CORE_DEVICE_H
> +#define _CORE_DEVICE_H
> +
> +#include <linux/list.h>
> +#include <linux/ioport.h>
> +#include <linux/of.h>
> +
> +struct core_device_id {
> +	const char		*name;
> +};
> +
> +enum core_device_class {
> +	CORE_DEV_CLASS_IRQ,
> +	CORE_DEV_CLASS_TIMER,
> +	CORE_DEV_CLASS_MAX		/* Do not use as a class */
> +};
> +
> +struct core_device {
> +	const char		*name;
> +	u32			num_resources;
> +	struct resource		*resource;
> +#ifdef CONFIG_OF
> +	struct device_node	*of_node;
> +#endif
> +	struct list_head	entry;
> +};
> +
> +struct core_driver {
> +	int			(*init)(struct core_device *);
> +	struct core_device_id	*ids;
> +};
> +
> +void core_device_register(enum core_device_class class,
> +			  struct core_device *dev);
> +void core_driver_init_class(enum core_device_class class,
> +			    void (*sort)(struct list_head *));
> +#ifdef CONFIG_OF
> +void of_core_device_populate(enum core_device_class class,
> +			     struct of_device_id *matches);
> +#else
> +static inline void of_core_device_populate(enum core_device_class class,
> +					   struct of_device_id *matches)
> +{
> +}
> +#endif
> +
> +struct core_driver_setup_block {
> +	enum core_device_class	class;
> +	struct core_driver	*drv;
> +};
> +
> +#define core_driver_register(cls, drv)					\
> +static struct core_driver_setup_block __core_driver_block_##cls##_##drv	\
> +	__used __section(.init.core_driver)				\
> +	__attribute__((aligned((sizeof(long)))))			\
> +	= { cls, &drv }
> +
> +#endif
> -- 
> 1.7.0.4
> 
> 
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