Re: [PATCH v2 5/9] dt-bindings: iio: dac: add ad3552r axi-dac compatible

[Krzysztof Kozlowski <krzk@kernel.org>]

On 06/09/2024 18:42, David Lechner wrote:
> On 9/6/24 11:36 AM, Krzysztof Kozlowski wrote:
>> On 06/09/2024 16:04, David Lechner wrote:
>>> On 9/6/24 8:52 AM, Nuno Sá wrote:
>>>> On Fri, 2024-09-06 at 14:13 +0200, Krzysztof Kozlowski wrote:
>>>>> On 06/09/2024 13:53, Nuno Sá wrote:
>>>>>> On Fri, 2024-09-06 at 11:37 +0200, Krzysztof Kozlowski wrote:
>>>>>>> On 06/09/2024 11:11, Angelo Dureghello wrote:
>>>>>>>> Hi Krzysztof,
>>>>>>>>
>>>>>>>> On 06/09/24 9:22 AM, Krzysztof Kozlowski wrote:
>>>>>>>>> On Thu, Sep 05, 2024 at 05:17:35PM +0200, Angelo Dureghello wrote:
>>>>>>>>>> From: Angelo Dureghello <adureghello@baylibre.com>
>>>>>>>>>>
>>>>>>>>>> Add a new compatible for the ad3552r variant of the generic DAC IP.
>>>>>>>>>>
>>>>>>>>>> The ad3552r DAC IP variant is very similar to the generic DAC IP,
>>>>>>>>>> register map is the same, but some register fields are specific to
>>>>>>>>>> this IP, and also, a DDR QSPI bus has been included in the IP.
>>>>>>>>>>
>>>>>>>>>> Signed-off-by: Angelo Dureghello <adureghello@baylibre.com>
>>>>>>>>>> ---
>>>>>>>>>>   Documentation/devicetree/bindings/iio/dac/adi,axi-dac.yaml | 1 +
>>>>>>>>>>   1 file changed, 1 insertion(+)
>>>>>>>>>>
>>>>>>>>>> diff --git a/Documentation/devicetree/bindings/iio/dac/adi,axi-dac.yaml
>>>>>>>>>> b/Documentation/devicetree/bindings/iio/dac/adi,axi-dac.yaml
>>>>>>>>>> index a55e9bfc66d7..c0cccb7a99a4 100644
>>>>>>>>>> --- a/Documentation/devicetree/bindings/iio/dac/adi,axi-dac.yaml
>>>>>>>>>> +++ b/Documentation/devicetree/bindings/iio/dac/adi,axi-dac.yaml
>>>>>>>>>> @@ -24,6 +24,7 @@ properties:
>>>>>>>>>>     compatible:
>>>>>>>>>>       enum:
>>>>>>>>>>         - adi,axi-dac-9.1.b
>>>>>>>>>> +      - adi,axi-dac-ad3552r
>>>>>>>>> I am sorry, but what is the product here? It looks like either wrong
>>>>>>>>> order or even completely redundant. What is ad3552r?
>>>>>>>>>
>>>>>>>>> And why versions are mixed with real products but without any
>>>>>>>>> compatibility. What does the version express in such case?
>>>>>>>>
>>>>>>>> dac-ad3552r IP (fpga) is a variant of the dac IP, very similar,
>>>>>>>> about the version, it still reads as 9.1.b
>>>>>>>>
>>>>>>>> so i can eventually change it to:
>>>>>>>>
>>>>>>>> adi,axi-dac-ad3552-9.1.b
>>>>>>>>
>>>>>>>> Should be more correct.
>>>>>>>
>>>>>>> No. First ad3552r is the product, so axi-dac is redundant. Second why
>>>>>>> adding versions if you have product names? Versioning was allowed
>>>>>>> because apparently that's how these are called, but now it turns out it
>>>>>>> is not version but names.
>>>>>>>
>>>>>>
>>>>>> Let me try to explain on how this whole thing works...
>>>>>>
>>>>>> We have a generic FPGA IP called axi-dac (same story is true for the other axi-
>>>>>> adc
>>>>>> IP) which adds some basic and generic capabilities like DDS (Direct digital
>>>>>> synthesis) and the generic one is the compatible existing now. This IP is a so
>>>>>> called
>>>>>> IIO backend because it then connects to a real converter (in this case DACs)
>>>>>> extending it's capabilities and also serving as an interface between another
>>>>>> block
>>>>>> (typical DMA as this is used for really high speed stuff) and the device. Now,
>>>>>> depending on the actual device, we may need to add/modify some features of the IP
>>>>>> and
>>>>>> this is what's happening for the ad3552r DAC (it's still build on top of the 
>>>>>
>>>>> What is "ad3552"? DAC right? Then as I said axi-dac is redundant. We do
>>>>> not call ti,tmp451 a ti,sensor-tmp451, right?
>>>>>
>>>>
>>>> Yes, I agree the DAC part is redundant. But I think the axi prefix (or suffix) is
>>>> meaningful to differentiate it from the bindings for the device itself.
>>>>
>>> The binding is for this [1] IP core. The documentation calls the core
>>> "AXI AD3552R", so I agree that "adi,axi-ad2552r" is the most sensible
>>> compatible name.
>>>
>>> http://analogdevicesinc.github.io/hdl/library/axi_ad3552r/index.html
>>
>> I don't see any AXI here:
>> https://www.analog.com/en/products/ad3552r.html
>> Neither here:
>> https://www.analog.com/media/en/technical-documentation/data-sheets/ad3552r.pdf
>>
>> Are these different?
> 
> 
> Yes, they are different. AD2553R is the DAC chip itself. But "AXI AD2553R" is an
> FPGA IP block designed specifically for use with that chip.

OK, this makes sense now. The commit msg said nothing about it. No
distinction and rather confusing "The ad3552r DAC IP".

Best regards,
Krzysztof