[PATCH v1 2/8] spi: dw: Add device tree properties for fields in CTRL0

[Sean Anderson <seanga2@gmail.com>]

On 3/21/20 11:13 PM, Marek Vasut wrote:
> On 3/22/20 4:08 AM, Sean Anderson wrote:
>> On 3/21/20 11:04 PM, Marek Vasut wrote:
>>> Could be a different revision of the IP. This is usually handled by
>>> using SoC-specific compatible strings, see e.g. Linux
>>> Documentation/devicetree/bindings/usb/renesas,usb3-peri.yaml
>>>
>>> You don't want to encode register layout in the DT.
>>
>> Ok, then I think adding compatible strings would be the cleanest.
>>
>>>
>>>> It is possible to
>>>> add several compatible strings like "kendryte,k210-spi3".
>>>
>>> Why ?
>>
>> See below.
>>
>>>
>>>> I chose this
>>>> method because the bitfields are different for spi0 and spi1, spi2, and
>>>> spi3. If there are other incompatibilities discovered, then it may make
>>>> more sense to use different strings. Another option could have been to
>>>> use the DW_SPI_VERSION field to detect different controllers, but it is
>>>> the same among all the controllers on the K210. 
>>>
>>> The controllers on the same SoC have different register layout ?
>>>
>>
>> Yup!
>>
>> Don't ask me why.
> 
> Now that is truly an odd design. Is there a datasheet for this SoC ?

Nope. Everything has been done referencing their sdk.

In hindsight, porting this board was a poor decision because of all the
hoops I've had to jump through due to the absence of documentation.
Unfortunately, it's probably the only budget risc-v board with S-mode
until the end of the year or so.

> You might be able to somehow enumerate those controllers in DT and
> derive their layout from that enumeration or somesuch I think.

So like derive it from the sequence number? I'd rather do this in a more
standard way, if possible.

--Sean