Re: [PATCH v2 04/22] of/platform: add of_platform_device_find()

[Tomeu Vizoso <tomeu.vizoso@collabora.com>]

On 28 July 2015 at 15:39, Rob Herring <robherring2@gmail.com> wrote:
> On Tue, Jul 28, 2015 at 8:19 AM, Tomeu Vizoso
> <tomeu.vizoso@collabora.com> wrote:
>> From an arbitrary node in the tree, find the enclosing node that
>> corresponds to a platform device, as registered by
>> of_platform_populate().
>>
>> This can be used to find out what device needs to be probed so the
>> dependency described by a given node is made available.
>>
>> Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
>> ---
>>
>> Changes in v2:
>> - Move the logic for finding a platform device from its firmware node to
>>   of/platform.c as it's not needed for ACPI nodes.
>>
>>  drivers/of/platform.c       | 60 +++++++++++++++++++++++++++++++++++++++++++++
>>  include/linux/of_platform.h |  1 +
>>  2 files changed, 61 insertions(+)
>>
>> diff --git a/drivers/of/platform.c b/drivers/of/platform.c
>> index ff27494cda8c..89c5cd513027 100644
>> --- a/drivers/of/platform.c
>> +++ b/drivers/of/platform.c
>> @@ -501,6 +501,66 @@ void of_platform_depopulate(struct device *parent)
>>  }
>>  EXPORT_SYMBOL_GPL(of_platform_depopulate);
>>
>> +static bool of_is_platform(struct device_node *np)
>> +{
>> +       int count;
>> +
>> +       count = of_property_count_strings(np, "compatible");
>> +
>> +       /* The node has to have a compatible string */
>> +       if (!count)
>> +               return false;
>> +
>> +       /* But it cannot be just a simple memory-mapped bus */
>> +       if (count == 1 && of_match_node(of_default_bus_match_table, np))
>> +               return false;
>> +
>> +       /* But AMBA devices aren't platform devices */
>> +       if (of_device_is_compatible(np, "arm,primecell"))
>> +               return false;
>> +
>> +       /* Node is immediately below root */
>> +       if (!np->parent || !np->parent->parent)
>> +               return true;
>> +
>> +       /* If it's a node in a simple memory-mapped bus */
>> +       if (of_match_node(of_default_bus_match_table, np->parent))
>> +               return true;
>
> This seems really fragile.

I think this finding logic matches the logic for registering platform
devices in of_platform_populate and also what is documented in
Documentation/devicetree/usage-model.txt.

> What about platform devices which are
> children of MFDs but are not "simple-mfd"?

This code should deal fine with those (the boards I tested with do
have them). It probes the mfd master, and that in turn will call
mfd_add_devices causing the target device to be probed.

> Does of_find_device_by_node not work for you?

Well, the dependencies aren't always platform devices, that's why I
need to go up the tree until I find a node that corresponds to a
platform device that I can query and probe.

If I had a way to get, say, a i2c device from its fwnode then I would
just need to make sure that a device's parent is probed before probing
it and everything would be cleaner in the OF case.

> That is probably not the
> most efficient search, but we could fix that. We could add struct
> device ptr to struct device_node and check without searching for
> example.

That would be great, but I thought there was an issue with a OF node
being able to be related to more than one struct device (but I haven't
found this myself yet).

Thanks,

Tomeu

> Rob
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