Re: [PATCH v7 1/7] spi: dt-bindings: Add spi-device-addr peripheral property

[David Lechner]

On 7/28/26 11:10 AM, Conor Dooley wrote:
> On Sat, Jul 25, 2026 at 11:04:45PM +0100, Jonathan Cameron wrote:
>> On Sat, 25 Jul 2026 15:55:01 -0500
>> David Lechner <dlechner@xxxxxxxxxxxx> wrote:
>>
>>> On 7/22/26 2:54 AM, Janani Sunil wrote:
>>>> Some SPI devices support sharing a single chip select across multiple
>>>> physical chips by encoding a device address in the SPI frame itself.
>>>> Add the generic spi-device-addr property for describing these hardware
>>>> addresses. The property is placed on the SPI peripheral node and may
>>>> contain multiple addresses.
>>>>
>>>> Signed-off-by: Janani Sunil <janani.sunil@xxxxxxxxxx>
>>>> ---
>>>>  Documentation/devicetree/bindings/spi/spi-peripheral-props.yaml | 7 +++++++
>>>>  1 file changed, 7 insertions(+)
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/spi/spi-peripheral-props.yaml b/Documentation/devicetree/bindings/spi/spi-peripheral-props.yaml
>>>> index 880a9f624566..b59d047cf117 100644
>>>> --- a/Documentation/devicetree/bindings/spi/spi-peripheral-props.yaml
>>>> +++ b/Documentation/devicetree/bindings/spi/spi-peripheral-props.yaml
>>>> @@ -142,6 +142,13 @@ properties:
>>>>      minItems: 2
>>>>      maxItems: 4
>>>>  
>>>> +  spi-device-addr:
>>>> +    $ref: /schemas/types.yaml#/definitions/uint32-array
>>>> +    description:
>>>> +      Device addresses used when multiple peripherals share a single chip
>>>> +      select. The array allows one logical peripheral to comprise multiple
>>>> +      physical devices, with one address per device.  
>>>
>>> "per physical device" for clarity.
>>>
>>
>> We may end up relaxing that again if multichip packages start doing this.
>> Fine to add that clarification for now. We can revisit when / if it ever
>> needs that relaxing.
>>
>>>> +
>>>>    st,spi-midi-ns:
>>>>      deprecated: true
>>>>      description: |
>>>>   
>>>
>>> If there is nothing useful the SPI core code can do with this information,
>>> I'm not entirely convinced that this needs to be a common property.
>>
>> I think being common does make some sense from a standarization point of
>> view and it isn't obvious where to put it other than under spi.
>>
>>>
>>> And this only allows for one logical device. If we wanted to treat each
>>> address as a logical device (all with same CS), we would need #address-cells = <2>;
>>> instead where the DT "address" is two values, the CS and the device address.
>>
>> Ah.  Good point for the adc@address or similar needing to match a combination
>> of CS and spi-device-addr.  Conor any thoughts on how this would be done?
> 
> I'm sorry, I don't quite understand. Why do you want to support both of
> these representations? Hardware wise both of these things would be
> describing the same setup, so allowing this alternate "multiple logical
> device" typically is not permitted. What even is the use case of it?
> Does it matter at all if you have one or more logical devices from a
> consumer perspective?
> 
> I do have an idea of how to solve the adc@address problem (you can do
> adc@address,spi-device-address like some other devices) but as I said I
> don't get why it would be needed.

I would expect that if such a device was intended to be used as individual
logical devices that they would just be wired up each with their own chip
select rather than sharing one.

The only reason I can think of actually needing adc@address,spi-device-address
would be on a system that was really short on pins on the MCU.

So not saying that we need it right now. Just wanted to make sure we were
intentional about saying we don't need it if we don't.