[PATCH 02/11] misc: Versatile Express config bus infrastructure

[Arnd Bergmann]

On Tuesday 04 September 2012, Pawel Moll wrote:
> On Mon, 2012-09-03 at 22:17 +0100, Arnd Bergmann wrote:
> > On Monday 03 September 2012, Pawel Moll wrote:

> > > --- a/drivers/misc/Kconfig
> > > +++ b/drivers/misc/Kconfig
> > > @@ -517,4 +517,5 @@ source "drivers/misc/lis3lv02d/Kconfig"
> > >  source "drivers/misc/carma/Kconfig"
> > >  source "drivers/misc/altera-stapl/Kconfig"
> > >  source "drivers/misc/mei/Kconfig"
> > > +source "drivers/misc/vexpress/Kconfig"
> > >  endmenu
> > > diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
> > > index b88df7a..49964fd 100644
> > > --- a/drivers/misc/Makefile
> > > +++ b/drivers/misc/Makefile
> > > @@ -50,3 +50,4 @@ obj-y				+= carma/
> > >  obj-$(CONFIG_USB_SWITCH_FSA9480) += fsa9480.o
> > >  obj-$(CONFIG_ALTERA_STAPL)	+=altera-stapl/
> > >  obj-$(CONFIG_INTEL_MEI)		+= mei/
> > > +obj-y				+= vexpress/
> > 
> > This does not look like something that should go to drivers/misc (well,
> > basically nothing ever does). How about drivers/mfd or drivers/bus instead?
> 
> I don't see drivers/bus in 3.6-rc4? If there will be such thing, I guess
> I can move config_bus.c to drivers/bus/vexpress-config.c, display.c to
> drivers/video/vexpress-display.c (see my other answer), sysreg.c to
> drivers/mfd/vexpress-sysreg.c (it is a multifunction device indeed, not
> argument about that), but reset.c seems to me should stay as
> drivers/misc/vexpress-reset.c - it's hardly a mfd...

We're adding drivers/bus in v3.7, I already have another bus driver in
the arm-soc tree.

The reset code can probably just go to arch/arm/mach-vexpress though,
we do the same for the reset code on all other platforms.

> > > +#define ADDR_TO_U64(addr) \
> > > +		(((u64)(addr).site << 32) | ((addr).position << 24) | \
> > > +		((addr).dcc << 16) | (addr).device)
> > > +
> > > +static bool vexpress_config_early = true;
> > > +static DEFINE_MUTEX(vexpress_config_early_mutex);
> > > +static LIST_HEAD(vexpress_config_early_drivers);
> > > +static LIST_HEAD(vexpress_config_early_devices);
> > 
> > What is the reason for needing early devices that you have to keep in a list
> > like this? If it's only for setup purposes, it's probably easier to
> > have a platform hook that probes the hardware you want to initialize at boot
> > time and only start using the device method at device init time.
> 
> Funnily enough the first version didn't have anything "early related"...
> Till I actually defined the real clock dependency in the tree :-(
> 
> So it's all about clocks, that must be available really early. The
> particular problem I faced was the amba_probe() trying to enable
> apb_pclk of each device and failing...
> 
> Now, during the clock registration the device model is not initialized
> yet, so I can't do normal devices registration. I've stolen some ideas
> from the early platform bus code...

Maybe you can change amba_probe() to provide a -EPROBE_DEFER return
code to the caller when the clock is not yet there, it should then
just come back later.

> > > +static int vexpress_config_match(struct device *dev, struct device_driver *drv)
> > > +{
> > > +	struct vexpress_config_device *vecdev = to_vexpress_config_device(dev);
> > > +	struct vexpress_config_driver *vecdrv = to_vexpress_config_driver(drv);
> > > +
> > > +	if (vecdrv->funcs) {
> > > +		const unsigned *func = vecdrv->funcs;
> > > +
> > > +		while (*func) {
> > > +			if (*func == vecdev->func)
> > > +				return 1;
> > > +			func++;
> > > +		}
> > > +	}
> > > +
> > > +	return 0;
> > > +}
> > > +
> > > +static struct device vexpress_config_bus = {
> > > +	.init_name = "vexpress-config",
> > > +};
> > 
> > No static devices in new code please. Just put it into the device tree.
> 
> Hm. This is just a dummy device serving as a default parent, similarly
> to:
> 
> struct device platform_bus = {
>         .init_name      = "platform",
> };
> EXPORT_SYMBOL_GPL(platform_bus);

The platform bus is very special, you should try not to use it as an
example for other buses ;-)
 
> Without that I can see two options:
> 
> 1. Create some kind of a device (platform?) for the dcc/mcc node and use
> it as a parent.
> 2. Scan the device tree "downwards" searching for a node that has a
> device already associated with it (but this may not work at the early
> stage).

I think 1. would be logical. The device should actually be created
by the device tree probe anyway.

> > > +struct bus_type vexpress_config_bus_type = {
> > > +	.name = "vexpress-config",
> > > +	.match = vexpress_config_match,
> > > +};
> > 
> > What is the reason for having a separate bus_type here?
> > Is this a discoverable bus? If it is, why do you need a
> > device tree binding for the child devices?
> 
> It is not a discoverable bus, but the devices are very different from
> the "normal" platform devices and have specific read/write interface, so
> it seemed to me that a separate bus would make sense. And I didn't want
> to reinvent the wheel with my own "device/driver model".

Not introducing a different way to do devices is good, but I don't think
that using something else than platform devices buys you much. If it's not
discoverable, this driver does not look all that different from an MFD
(which is based on platform devices).

A new bus type is typically used only for cases where you have multiple
different bus drivers and multiple different device drivers, and want a
bus layer to proxy between them. In your case, it seems you have only
a single device driver providing devices, and it just gets them by looking
at the device tree, so there is no real need for a bus_type.

> > > +#define VEXPRESS_COMPATIBLE_TO_FUNC(_compatible, _func) \
> > > +	{ \
> > > +		.compatible = "arm,vexpress-config," _compatible, \
> > > +		.data = (void *)VEXPRESS_CONFIG_FUNC_##_func \
> > > +	}
> > > +
> > > +static struct of_device_id vexpress_config_devices_matches[] = {
> > > +	VEXPRESS_COMPATIBLE_TO_FUNC("osc", OSC),
> > > +	VEXPRESS_COMPATIBLE_TO_FUNC("volt", VOLT),
> > > +	VEXPRESS_COMPATIBLE_TO_FUNC("amp", AMP),
> > > +	VEXPRESS_COMPATIBLE_TO_FUNC("temp", TEMP),
> > > +	VEXPRESS_COMPATIBLE_TO_FUNC("reset", RESET),
> > > +	VEXPRESS_COMPATIBLE_TO_FUNC("scc", SCC),
> > > +	VEXPRESS_COMPATIBLE_TO_FUNC("muxfpga", MUXFPGA),
> > > +	VEXPRESS_COMPATIBLE_TO_FUNC("shutdown", SHUTDOWN),
> > > +	VEXPRESS_COMPATIBLE_TO_FUNC("reboot", REBOOT),
> > > +	VEXPRESS_COMPATIBLE_TO_FUNC("dvimode", DVIMODE),
> > > +	VEXPRESS_COMPATIBLE_TO_FUNC("power", POWER),
> > > +	VEXPRESS_COMPATIBLE_TO_FUNC("energy", ENERGY),
> > > +	{},
> > > +};
> > 
> > What is the purpose of this lookup? Can't you make the child devices get
> > probed by the compatible value?
> 
> Ok, there are two reasons for this table existence:
> 
> 1. vexpress_config_of_populate() below - I need a comprehensive list of
> compatible values to be able to search the tree and create respective
> devices.

I don't see why you need this list. Just call of_platform_populate or a
copy of that. It does not require the compatible values of the devices,
just the one for the parent.

> 2. Non-DT static devices - I need something to be able to match a driver
> with a device, and the "functions list" seemed appropriate.

How important is this case really, given that the driver has never been
supported and that the non-DT case is going away soon?

> > > +static void vexpress_config_of_device_add(struct device_node *node)
> > > +{
> > > +	int err;
> > > +	struct vexpress_config_device *vecdev;
> > > +	const struct of_device_id *match;
> > > +	u32 value;
> > > +
> > > +	if (!of_device_is_available(node))
> > > +		return;
> > > +
> > > +	vecdev = kzalloc(sizeof(*vecdev), GFP_KERNEL);
> > > +	if (WARN_ON(!vecdev))
> > > +		return;
> > > +
> > > +	vecdev->dev.of_node = of_node_get(node);
> > > +
> > > +	vecdev->name = node->name;
> > > +
> > > +	match = of_match_node(vexpress_config_devices_matches, node);
> > > +	vecdev->func = (unsigned)match->data;
> > > +
> > > +	err = of_property_read_u32(node->parent, "arm,vexpress,site", &value);
> > > +	if (!err)
> > > +		vecdev->addr.site = value;
> > > +
> > > +	err = of_property_read_u32(node->parent, "arm,vexpress,position",
> > > +			&value);
> > > +	if (!err)
> > > +		vecdev->addr.position = value;
> > > +
> > > +	err = of_property_read_u32(node->parent, "arm,vexpress,dcc", &value);
> > > +	if (!err)
> > > +		vecdev->addr.dcc = value;
> > > +
> > > +	err = of_property_read_u32(node, "reg", &value);
> > > +	if (!err) {
> > > +		vecdev->addr.device = value;
> > > +	} else {
> > > +		pr_err("Invalid reg property in '%s'! (%d)\n",
> > > +				node->full_name, err);
> > > +		kfree(vecdev);
> > > +		return;
> > > +	}
> > > +
> > > +	err = vexpress_config_device_register(vecdev);
> > > +	if (err) {
> > > +		pr_err("Failed to add OF device '%s'! (%d)\n",
> > > +				node->full_name, err);
> > > +		kfree(vecdev);
> > > +		return;
> > > +	}
> > > +}
> > > +
> > > +void vexpress_config_of_populate(void)
> > > +{
> > > +	struct device_node *node;
> > > +
> > > +	for_each_matching_node(node, vexpress_config_devices_matches)
> > > +		vexpress_config_of_device_add(node);
> > > +}
> > 
> > This is unusual. Why do you only add the matching devices rather than
> > all of them? Doing it your way also means O(n^2) rather than O(n)
> > traversal through the list of children.
> 
> Em, I'm not sure what do you mean... The idea is shamelessly stolen from
> of_irq_init() and of_clk_init()...

But those are not buses, they are infrastructure that is used across
buses. The regular way to do this is to register a driver for your
parent node and then just iterate over the children, in the way that
we do for e.g. i2c or spi buses.

> > > +EXPORT_SYMBOL(vexpress_config_device_register);
> > 
> > Why is this exported to non-GPL drivers? It looks like the only caller should be
> > in this file.
> 
> Hm. There's no hidden agenda behind the non-GPL export, if that's what
> you are afraid of ;-) Now, why it is exported at all? Because
> platform_device_register is, I suppose (you can tell that I was looking
> at the platform bus code ;-). The non-DT platform code is using it, so
> it can't be static, but I wouldn't really expect any module to use it.
> So I can make it EXPORT_SYMBOL_GPL or drop it, no problem.

Ok. I'd say just drop it then.

	Arnd