[U-Boot] [PATCH] fdt: Allow fdt_translate_address() to work with buses

[Stephen Warren]

On 01/04/2016 06:00 PM, Simon Glass wrote:
> Hi Stephen,
>
> On 4 January 2016 at 13:15, Stephen Warren <swarren at wwwdotorg.org> wrote:
>> On 01/03/2016 04:04 PM, Simon Glass wrote:
>>>
>>> It is common for I2C and SPI buses to have a single-cell address and a
>>> size
>>> of 0. These produce a warning at present. For example on snow:
>>>
>>> __of_translate_address: Bad cell count for gpc4
>>> __of_translate_address: Bad cell count for gpx0
>>> __of_translate_address: Bad cell count for gpv2
>>> __of_translate_address: Bad cell count for gpv4
>>>
>>> One of the nodes in question looks like this in part:
>>>
>>>          pinctrl_2: pinctrl at 10d10000 {
>>>                  #address-cells = <1>;
>>>                  #size-cells = <0>;
>>>                  gpv2: gpv2 {
>>>                          reg = <0x060>;
>>>                  };
>>>                  gpv4: gpv4 {
>>>                          reg = <0xc0>;
>>>                  };
>>>          };
>>>
>>> This is clearly valid so it looks like the conversion to use
>>> fdt_translate_address() in dev_get_addr() is not currently a good move.
>>
>>
>> To disable that, why not simply turn off CONFIG_OF_TRANSLATE on the affected
>> platforms? That's precisely why that config option was introduced when the
>> call to fdt_translate_address() was added to dev_get_addr()?
>>
>> That would prevent this patch from affecting platforms that don't trigger
>> this issue, this leaving the valid check in place.
>
> But since this breaks normal behaviour we don't know what platforms
> are affected. We have made CONFIG_OF_TRANSLATE the default. So this
> approach doesn't seem (in effect) any better than Przemyslaw's newer
> series, below.

It'd be better since it'd isolate the disabling of the feature only to 
those platforms that need it to work around bugs.

Still, if you're absolutely certain that this change will be reverted as 
soon as the release is made, that is probably OK.

>>> Przemyslaw Marczak sent three patches to resolve this for exynos boards:
>>>
>>> https://patchwork.ozlabs.org/patch/557008/
>>> https://patchwork.ozlabs.org/patch/557010/
>>> https://patchwork.ozlabs.org/patch/557009/
>>>
>>> But this involves creating a new function, and everyone will need to know
>>> when to use which one. Also the problem may affect other boards.
>>
>>
>> I suggest adding an extra parameter to dev_get_addr() (or whatever calls it)
>> that indicates the root of the address space. The check on #size-cells
>> should be skipped for that one node (or level of translation) but enabled
>> for all other levels. This way, there would be no need for anyone to choose
>> between functions; there'd only be one. Most cases (i.e. translation of MMIO
>> addresses) would simply pass 0 as the extra parameter (for the root node),
>> but in special cases where it's known translation is not expected to reach
>> the root MMIO space (e.g. I2C, SPI controllers), the controller node would
>> be passed in.
>
> How would the caller know this root?

I appear to have answered this already in response to one of 
Przemyslaw's emails.

 > It sounds plausible, but I do
> want to avoid complex rules. I think you are saying that buses that
> use their own address mechanism (i.e. not MMIO) must do something
> special. The current dev_get_addr() is really simple.

dev_get_addr() is simple yes, but also incorrect (to use in certain 
contexts, as currently implemented).

DT has special cases. Code that parses DT has to deal with them. To 
paraphrase some famous quote: Things should be as simple as possible, 
but no simpler.