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

[Marek Vasut]

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.

> It is possible to
> add several compatible strings like "kendryte,k210-spi3".

Why ?

> 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 ?

-- 
Best regards,
Marek Vasut