[PATCH 2/2] drivers/amba: probe via device tree

[Rob Herring]

Grant,

On 05/19/2011 06:39 PM, Grant Likely wrote:
> On Thu, May 19, 2011 at 06:30:23PM -0500, Rob Herring wrote:
>> Grant,
>>
>> On 05/19/2011 03:01 PM, Grant Likely wrote:
>>> On Thu, May 19, 2011 at 01:28:24PM -0500, Rob Herring wrote:
>>>> From: Rob Herring<rob.herring at calxeda.com>
>>>>
>>>> Add functions to parse the AMBA bus through the device tree.
>>>>
>>>> Based on the original version by Jeremy Kerr. This reworks the original amba
>>>> bus device tree probing to be more inline with how platform bus probing via
>>>> device tree is done using a match table.
>>>>
>>>> Cc: Jeremy Kerr<jeremy.kerr at canonical.com>
>>>> Cc: Grant Likely<grant.likely at secretlab.ca>
>>>> Signed-off-by: Rob Herring<rob.herring at calxeda.com>
>>>> ---
>>>>   drivers/amba/bus.c       |  133 ++++++++++++++++++++++++++++++++++++++++++++++
>>>>   include/linux/amba/bus.h |    7 +++
>>>>   2 files changed, 140 insertions(+), 0 deletions(-)
>>>>
>>>> diff --git a/drivers/amba/bus.c b/drivers/amba/bus.c
>>>> index 7025593..8e55754 100644
>>>> --- a/drivers/amba/bus.c
>>>> +++ b/drivers/amba/bus.c
>>>> @@ -13,6 +13,11 @@
>>>>   #include<linux/string.h>
>>>>   #include<linux/slab.h>
>>>>   #include<linux/io.h>
>>>> +#include<linux/of.h>
>>>> +#include<linux/of_irq.h>
>>>> +#include<linux/of_address.h>
>>>> +#include<linux/of_device.h>
>>>> +#include<linux/of_platform.h>
>>>>   #include<linux/pm.h>
>>>>   #include<linux/pm_runtime.h>
>>>>   #include<linux/amba/bus.h>
>>>> @@ -780,3 +785,131 @@ EXPORT_SYMBOL(amba_device_unregister);
>>>>   EXPORT_SYMBOL(amba_find_device);
>>>>   EXPORT_SYMBOL(amba_request_regions);
>>>>   EXPORT_SYMBOL(amba_release_regions);
>>>> +
>>>> +#ifdef CONFIG_OF
>>>> +int of_amba_device_create(struct device_node *node,struct device *parent)
>>>> +{
>>>> +	struct amba_device *dev;
>>>> +	const void *prop;
>>>> +	int i, ret;
>>>> +
>>>> +	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
>>>> +	if (!dev)
>>>> +		return -ENOMEM;
>>>> +
>>>> +	/* setup generic device info */
>>>> +	dev->dev.coherent_dma_mask = ~0;
>>>> +	dev->dev.of_node = node;
>>>> +	dev->dev.parent = parent;
>>>> +	of_device_make_bus_id(&dev->dev);
>>>> +
>>>> +	/* setup amba-specific device info */
>>>> +	dev->dma_mask = ~0;
>>>> +
>>>> +	/* Decode the IRQs and address ranges */
>>>> +	for (i = 0; i<   AMBA_NR_IRQS; i++)
>>>> +		dev->irq[i] = irq_of_parse_and_map(node, i);
>>>> +
>>>> +	ret = of_address_to_resource(node, 0,&dev->res);
>>>> +	if (ret)
>>>> +		goto err_free;
>>>> +
>>>> +	ret = amba_device_register(dev,&iomem_resource);
>>>> +	if (ret)
>>>> +		goto err_free;
>>>> +
>>>> +	/* Sanity check the arm,amba-deviceid value */
>>>> +	prop = of_get_property(node, "arm,amba-deviceid", NULL);
>>>> +	if (!prop)
>>>> +		dev_warn(&dev->dev, "arm,amba-deviceid property missing; "
>>>> +				    "probe gives 0x%08x.\n", dev->periphid);
>>>> +
>>>> +	if (prop&&   (dev->periphid != of_read_ulong(prop, 1)))
>>>> +		dev_warn(&dev->dev, "arm,amba-deviceid value (0x%08lx) and "
>>>> +				    "probed value (0x%08x) don't agree.",
>>>> +				    of_read_ulong(prop, 1), dev->periphid);
>>>> +
>>>> +	return 0;
>>>> +
>>>> +err_free:
>>>> +	kfree(dev);
>>>> +	return ret;
>>>> +}
>>>> +
>>>> +/**
>>>> + * of_amba_bus_create() - Create a device for a node and its children.
>>>> + * @bus: device node of the bus to instantiate
>>>> + * @matches: match table for bus nodes
>>>> + * disallow recursive creation of child buses
>>>> + * @parent: parent for new device, or NULL for top level.
>>>> + *
>>>> + * Recursively create devices for all the child nodes.
>>>> + */
>>>> +static int of_amba_bus_create(struct device_node *bus,
>>>> +			      const struct of_device_id *matches,
>>>> +			      struct device *parent)
>>>> +{
>>>> +	struct of_platform_prepare_data *prep;
>>>> +	struct device_node *child;
>>>> +	struct platform_device *dev;
>>>> +	int rc = 0;
>>>> +
>>>> +	/* Make sure it has a compatible property */
>>>> +	if (!of_get_property(bus, "compatible", NULL)) {
>>>> +		pr_debug("%s() - skipping %s, no compatible prop\n",
>>>> +			 __func__, bus->full_name);
>>>> +		return 0;
>>>> +	}
>>>> +
>>>> +	if (!of_match_node(matches, bus))
>>>> +		return 0;
>>>> +
>>>> +	dev = of_platform_device_create(bus, NULL, parent);
>>>> +	if (!dev)
>>>> +		return 0;
>>>
>>> Hahaha, I think I see where we're getting our models crossed.
>>>
>>> The use-case of of_amba_bus_populate should be that the device
>>> representing the amba bus (which will be a platform device) should
>>> have already been created before calling of_amba_bus_populate().
>>> of_amba_bus_populate should then be responsible for creating all the
>>> child devices that are on the AMBA bus.
>>>
>>
>> That was one option I had thought about. I happened to put amba call
>> first so I hit the issue. It's a bit fragile to require a certain
>> calling order.
>
> Yes, so the goal is not to require a calling order.
>
>>
>>> of_platform_populate does the same thing, except it has some added and
>>> *optional* helper logic that allows the populate code to dive deeper
>>> into the device hierarchy for any nodes that match the passed in
>>> device table.
>>>
>> That's a bit of an orthogonal problem. In my case, all devices are
>> created from the DT. This issue is scanning the devicetree multiple
>> times.
>>
>>> I'd actually like to be able to integrate AMBA population in
>>> of_platform_populate() when it encounters an AMBA bus, but I'm not
>>> sure the result will be pretty.  I haven't had a chance to try it.
>>>
>>
>> That seems like a bad idea to me. It's fine with 1 other bus type,
>> but if you had 10 others it would get messy.
>>
>> Perhaps scanning the tree for buses first and then scanning for
>> devices is a better solution.
>
> However, it would all work with one call if the match table passed
> into of_platform_populate() also included a populate hook for each bus
> type.  That way it still is up to the platform as to which bus types
> to probe.  Or a default list of bus types could be provided too.
>

Maybe we are looking this in the wrong way.

AMBA is not really the bus, but certain types of devices on the bus. 
Granted, it may actually be an AMBA bus vs. vendor bus (i.MX AIPS), but 
that is really transparent to s/w. Separating AMBA devices in the 
devicetree is really Linux requirements defining the devicetree 
structure. It is certainly conceivable that an OS could make no 
distinction. In my case, there is a mixture of regular platform devices 
and AMBA(Primecell really) devices all interleaved on the same bus.

Based on this, I think of_platform_populate should always just match 
against "simple-bus" and make the matches parameter define the device 
creation hook rather than the bus type. Or you could have both 
bus_matches and dev_matches parameters.

Rob