linux-kernel - Re: use IORESOURCE_REG resource type for non-translatable addresses in DT

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Message-ID: <53D7AA72.6010309@mm-sol.com>
Date:	Tue, 29 Jul 2014 17:06:42 +0300
From:	Stanimir Varbanov <svarbanov@...sol.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <rob.herring@...aro.org>,
	Rob Herring <robherring2@...il.com>,
	Lee Jones <lee.jones@...aro.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	linux-arm-kernel@...ts.infradead.org,
	Stephen Boyd <sboyd@...eaurora.org>,
	Mark Brown <broonie@...aro.org>
Subject: Re: use IORESOURCE_REG resource type for non-translatable addresses
 in DT

Arnd, thanks for the comments.

On 07/29/2014 03:00 PM, Arnd Bergmann wrote:
> On Tuesday 29 July 2014 14:42:31 Stanimir Varbanov wrote:
>>         taddr = of_translate_address(dev, addrp);
>> -       if (taddr == OF_BAD_ADDR)
>> -               return -EINVAL;
>> +       /*
>> +        * if the address is non-translatable to cpu physical address
>> +        * fallback to a IORESOURCE_REG resource.
>> +        */
>> +       if (taddr == OF_BAD_ADDR) {
>> +               memset(r, 0, sizeof(*r));
>> +               taddr = of_read_number(addrp, 1);
>> +               if (taddr == OF_BAD_ADDR)
>> +                       return -EINVAL;
>> +               r->start = taddr;
>> +               r->end = taddr + size - 1;
>> +               r->flags = IORESOURCE_REG;
>> +               r->name = name ? name : dev->full_name;
>> +               return 0;
>> +       }
>> +
> 
> I don't think that everything returning OF_BAD_ADDR makes sense
> to turn into IORESOURCE_REG. It could be an e.g. invalid DT
> representation, a node with #size-cells=<0>, or it could be
> something that gets translated one or more nodes up in the
> tree before it reaches a bus without a ranges property.
> 
> Also, you should not rely on #address-cells being hardcoded
> to <1> above.
> 

This was just an example. Of course it has many issues and probaly it is
wrong:) The main goal was to understand does IORESOURCE_REG resource
type and parsing the *reg* properties for non-translatable addresses are
feasible. And also does it acceptable by community and OF platform
maintainers.

> How about modifying of_get_address() rather than
> __of_address_to_resource() instead? You could introduce
> a new of_bus entry for each bus you expect to return
> an IORESOURCE_REG, or you could change of_bus_default_get_flags
> to return IORESOURCE_REG if the parent node has no ranges property
> and is not the root node.

IMO the clearer solution is to introduce a new of_bus bus. In that case
one possible problem will be how to distinguish the non-translatable and
the other buses. Also the *device_type* property is deprecated for non
PCI devices.

The second option will need to change the prototype of .get_flags method
to receive device_node structure.

Thoughts?

-- 
regards,
Stan
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