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

[Sean Anderson]

On 3/21/20 11:04 PM, Marek Vasut wrote:
> On 3/22/20 3:36 AM, Sean Anderson wrote:
>> On 3/21/20 9:51 PM, Marek Vasut wrote:
>>> On 3/5/20 8:19 PM, Sean Anderson wrote:
>>>> Some devices have different layouts for the fields in CTRL0 (e.g. the
>>>> Kendryte K210). Allow this layout to be configurable from the device tree.
>>>> The documentation has been taken from Linux.
>>>>
>>>> Signed-off-by: Sean Anderson <seanga2 at gmail.com>
>>>> Reviewed-by: Simon Glass <sjg at chromium.org>
>>>
>>> Can't you just have different compatible string for each SoC and derive
>>> the various fields based on that compatible string, instead of
>>> describing all the register bitfields in DT ?
>>>
>>> What does Linux do ?
>>>
>>
>> Linux only supports socfpga boards. I don't know if there is any
>> rhyme/reason to the shifting around of these fields.
> 
> 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.

--Sean