[U-Boot] [PATCH 0/3] dm: add dev_get_reg() for getting device node's reg

[Stephen Warren]

On 12/29/2015 01:47 AM, Przemyslaw Marczak wrote:
> Hello Stephen,
>
> On 12/16/2015 08:07 PM, Stephen Warren wrote:
>> On 12/16/2015 11:53 AM, Stephen Warren wrote:
>>> On 12/15/2015 09:32 AM, Przemyslaw Marczak wrote:
>>>> commit: dm: core: Enable optional use of fdt_translate_address()
>>>>
>>>> enables device's bus/child address translation method, depending
>>>> on bus 'ranges' property and including child 'reg' property.
>>>> This change makes impossible to decode the 'reg' for node with
>>>> '#size-cells' equal to 0.
>>>>
>>>> Such case is possible by the specification and is also used in U-Boot,
>>>> e.g. by I2C uclass or S5P GPIO - the last one is broken at present.
>>>
>>> Can you please explain the problem you're seeing in more detail? Without
>>> any context, my initial reaction is that this is simply a bug somewhere.
>>> That bug should be fixed, rather than introducing new APIs to hide the
>>> problem.
>>
>> Ah, I guess the problem is caused by the following code in
>> __of_translate_address():
>>
>>      bus->count_cells(blob, parent, &na, &ns);
>>      if (!OF_CHECK_COUNTS(na, ns)) {
>>          printf("%s: Bad cell count for %s\n", __FUNCTION__,
>>
>
> Yes, and this is what my previous patch 'fixes'.
>
> [1] https://patchwork.ozlabs.org/patch/537372/
>
> However Linux makes the translate in the same way.
>
>> That's because the function assumes it's called for MMIO addresses.
>> However, reg values for I2C devices aren't MMIO addresses, so those
>> assumptions don't apply. So, there is an argument for introducing some
>> new functionality. I'm not sure that a whole new function is the correct
>> way to go though. Rather, the existing translation functions should be
>> enhanced to know the location of root of the address space that contains
>> the address that's being translated. Then, translation can stop there.
>
> This is okay but then, all device tree blobs should be defined in a
> proper way.

Well, why shouldn't that be true? There are rules for how DTs must be 
constructed. Nobody should expect DTs that violate those rules to work 
in any particular way.

> The problem is, that there are some additions and various assumptions in
> the drivers, e.g. the exynos gpio driver (s5p_gpio.c) is checking the
> reg's property value for each bank. But the driver in Linux hardcodes
> those values, however for both cases this is wrong, because the gpio
> regs could be mapped with ranges.

It sounds like there are many bugs to fix:-)

> Even that issues above, I would prefer introduce a function or modify
> the existing one to allow keeping this as it is.

Adding an extra function sounds OK, although I stand by my comment that 
the caller should pass in a parameter indicating the root of the address 
space, so that both #address-cells and #size-cells can be checked all 
the way up the chain, and #size-cells should only be allowed to be 0 at 
the root of the translation, not at any intermediate point.

>> Something like skipping the check on ns in the above code if parent ==
>> addr_space_root_offset, and also terminating the for (;;) loop in that
>> function under a similar condition.
>>
>> This would allow for translation to occur for buses other than the CPU's
>> root MMIO space, yet not attempt to translate across known address space
>> boundaries (i.e. where address translation is known to be impossible).
>
> To achieve this functionality, it should be enough to take my first
> patch [1]. And then if no "ranges" is defined, then we have 1:1
> translation.

I don't think so; that patch removes all checks on #size-cells rather 
than only removing/ignoring the check at the root of the address space.

> I think, that it is safe, but then we will have a different assumptions,
> than in the Linux - is it acceptable?

Both Linux and U-Boot should conform to the DT specification. So, if 
there's a difference between the two, there's likely a bug.