Re: [PATCH v4 6/7] dt-bindings: cache: r9a07g043f-l2-cache: Add DT binding documentation for L2 cache controller

Krzysztof Kozlowski
2022-11-25T15:55:28Z

On 25/11/2022 13:25, Conor Dooley wrote:
> On Fri, Nov 25, 2022 at 01:12:18PM +0100, Krzysztof Kozlowski wrote:
>> On 25/11/2022 11:34, Lad, Prabhakar wrote:
>>>>> +/* Device, Non-bufferable */
>>>>> +#define AX45MP_PMACFG_MTYP_DEV_NON_BUF (0 << 2)
>>>>> +/* Device, bufferable */
>>>>> +#define AX45MP_PMACFG_MTYP_DEV_BUF (1 << 2)
>>>>> +/* Memory, Non-cacheable, Non-bufferable */
>>>>> +#define AX45MP_PMACFG_MTYP_MEM_NON_CACHE_NON_BUF (2 << 2)
>>>>> +/* Memory, Non-cacheable, Bufferable */
>>>>> +#define AX45MP_PMACFG_MTYP_MEM_NON_CACHE_BUF (3 << 2)
>>>>
>>>> What are all these? They don't look like flags, because 3 = 1 | 2...
>>>> they don't look like constants, because we do not use shifts in
>>>> constants. Are these some register values? I also do not see the header
>>>> being used in the code, so why having a bindings header if it is not
>>>> used (DTS is not usage...)?
>>>>
>>> These are register bit values for the MTYP[5:2] field. The DTS example
>>> in the binding doc (above) uses these macros. I haven't included the
>>> DTS/I patches with this patchset yet do think I should?
>>
>> Then why storing it as bindings? Bindings headers describe the interface
>> implemented by drivers and used by DTS, but this is not implemented by
>> drivers.
>
> IIUC, some of these properties are non-discoverable attributes of the
> cache controller. I see two things that could be done here that are
> "better" than #defining bits:

I did not comment about properties. I comment about constants. Why
register values/offsets/addresses are in this particular case suitable
for binding headers?

> - add an RZ/Five specific compatible and use match data to set the
> attributes which is only possible if the pma-regions are set on a
> per SoC basis
> - make pma-regions into a child node, in which andestech,non-cacheable
> andestech,non-bufferable etc are properties of the child node
>
> Prabhakar, does that make sense or am I off with my understanding of the
> attributes?

Best regards,
Krzysztof