Re: [PATCH 2/2] dt-bindings: i2c: cadence: Document `cdns,fifo-depth` property

[Lars-Peter Clausen <lars@metafoo.de>]

Thanks for the review.

On 2/5/23 23:41, Krzysztof Kozlowski wrote:
> On 06/02/2023 00:02, Lars-Peter Clausen wrote:
>> The depth of the FIFO of the Cadence I2C controller IP is a synthesis
>> configuration parameter. Different instances of the IP can have different
>> values. For correct operation software needs to be aware of the size of the
>> FIFO.
> Cannot this be inferred from compatible?

The compatible string currently encodes the version of the IP core. The 
FIFO depth is an orthogonal setting. You could of course encode both the 
version and FIFO depth as part of the compatible string. But you'd end 
up with a combinatorial explosion of compatible strings. Like

cdns,i2c-r1p10-fifo-depth-2, ... cdns,i2c-r1p10-fifo-depth-16, ..., 
cdns,i2c-r1p10-fifo-depth-256, cdns,i2c-r1p14-fifo-depth-2, ... 
cdns,i2c-r1p14-fifo-depth-16, ..., cdns,i2c-r1p14-fifo-depth-256,

>
>> Add the documentation for the devicetree property that describes the FIFO
>> depth of the IP core.
>>
>> The default value of 16 is for backwards compatibility reasons with
>> existing hardware descriptions where this property is not specified and
>> software has assumed that the FIFO depth is 16.
>>
>> Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
>> ---
>>   Documentation/devicetree/bindings/i2c/cdns,i2c-r1p10.yaml | 8 ++++++++
>>   1 file changed, 8 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/i2c/cdns,i2c-r1p10.yaml b/Documentation/devicetree/bindings/i2c/cdns,i2c-r1p10.yaml
>> index 2e95cda7262a..3daa2fa73257 100644
>> --- a/Documentation/devicetree/bindings/i2c/cdns,i2c-r1p10.yaml
>> +++ b/Documentation/devicetree/bindings/i2c/cdns,i2c-r1p10.yaml
>> @@ -38,6 +38,12 @@ properties:
>>       description: |
>>         Input clock name.
>>   
>> +  cdns,fifo-depth:
>> +    description:
>> +      Size of the data FIFO in words.
>> +    $ref: "/schemas/types.yaml#/definitions/uint32"
> Drop quotes.
>
>> +    default: 16
> maximum
> minimum?

Will add a enum, since it has to be a power of two.