linux-kernel - Re: [RFC PATCH 3.7.0-rc2] dt: match id-table before creating platform device

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Message-ID: <5087C6DA.1070706@st.com>
Date:	Wed, 24 Oct 2012 11:45:46 +0100
From:	Srinivas KANDAGATLA <srinivas.kandagatla@...com>
To:	Rob Herring <robherring2@...il.com>
Cc:	Grant Likely <grant.likely@...retlab.ca>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 3.7.0-rc2] dt: match id-table before creating platform
 device

On 23/10/12 14:15, Rob Herring wrote:
> Adding lkml. DT patches should go to both lists.
>
> On 10/23/2012 05:30 AM, Srinivas KANDAGATLA wrote:
>> From: Srinivas Kandagatla <srinivas.kandagatla@...com>
>>
>> As part of of_platform_populate call, the existing code iterates each
>> child node and then creates a platform device for each child, however
>> there is bug in the code which does not check the match table before
>> creating the platform device. This might result creating two platfrom
>> devices and also invoking driver probe twice, which is incorrect.
>>
>> This patch moves a existing of_match_node check to start of the function
>> to fix the bug, doing this way will return immediately without creating
>> any datastructures if the child does not match the supplied match-table.
>>
>> Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@...com>
>> ---
>>  drivers/of/platform.c |    5 ++++-
>>  1 files changed, 4 insertions(+), 1 deletions(-)
>>
>> diff --git a/drivers/of/platform.c b/drivers/of/platform.c
>> index b80891b..1aaa560 100644
>> --- a/drivers/of/platform.c
>> +++ b/drivers/of/platform.c
>> @@ -367,6 +367,9 @@ static int of_platform_bus_create(struct device_node *bus,
>>  		return 0;
>>  	}
>>  
>> +	if (!of_match_node(matches, bus))
>> +		return 0;
>> +
> This is not right. This function is recursive and this change would
> break that. 
You are correct, this change might break the functionality.
> Perhaps we could only call of_platform_device_create_pdata
> if !of_match_node instead, but I'm not completely sure that would be the
> right thing to do. 
I did try to do the same thing in the patch.
May be I should have moved check just before calling
of_platform_device_create_pdata?
> There's also some historical things we have to
> support which is why we have of_platform_populate and of_platform_bus_probe.
Am just trying to understand the difference between of_platform_populate
and of_platform_bus_probe.
Looking at the function documentation, which states
of_platform_bus_probe will only create children of the root which are
selected by the @matches argument.

of_platform_populate walks the device tree and creates devices from
nodes.  It differs in that it follows the modern convention of requiring
all device nodes to have a 'compatible' property, and it is suitable for
creating devices which are children of the root node.

Lets say If we call of_platform_populate(NULL, match_table, NULL, NULL)
on a device trees like the below with
struct of_device_id match_table[] = {
    { .compatible = "simple-bus", }
    {}
};

parent@0{
    compatible    = "xxx,parent1", "simple-bus";
    ...
    child@0 {
        compatible    = "xxx,child0", "simple-bus";
        ...
    };
    child@1 {
        compatible    = "xxx,child1";
        ...
    };
    child@2 {
        compatible    = "xxx,child2", "simple-bus";
        ...
    };
};

of_platform_bus_probewould create platform-devices for parent@0,
child@...d child@2
where as
of_platform_populate would create platform-devices for parent@0,
child@0, child@1 and child@2 nodes.

So the question is
why do we need to have @matches argument to of_platform_populate in the
first place, if it creates all the devices by walking the dt nodes?

It is bit confusion, As some platforms use of_platform_populate(NULL,
of_default_bus_match_table, NULL, NULL) assuming that only matching
nodes will end up having platform device.
Also
some platforms use of_platform_bus_probe(NULL, match_table, NULL), 
where match table is of_default_bus_match_table.

IMO, we could do two things to avoid this confusion in future.

1. Remove matches from of_platform_populate
2. add Lookup argument to of_platform_bus_probe

What do you think?

--srini




>
> Rob
>
>>  	auxdata = of_dev_lookup(lookup, bus);
>>  	if (auxdata) {
>>  		bus_id = auxdata->name;
>> @@ -379,7 +382,7 @@ static int of_platform_bus_create(struct device_node *bus,
>>  	}
>>  
>>  	dev = of_platform_device_create_pdata(bus, bus_id, platform_data, parent);
>> -	if (!dev || !of_match_node(matches, bus))
>> +	if (!dev)
>>  		return 0;
>>  
>>  	for_each_child_of_node(bus, child) {
>>
>
>

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