Re: [PATCH v5 1/3] dt-bindings: spi: Add spi,device-addr peripheral property

[David Lechner]

Note that a few subsystems, including spi want the subject
to be `spi: dt-bindings:` rather than the other way around.

See https://www.kernel.org/doc/html/latest/devicetree/bindings/submitting-patches.html


On 7/1/26 1:29 PM, Jonathan Cameron wrote:
> On Wed, 1 Jul 2026 12:04:37 +0100
> Conor Dooley <conor@xxxxxxxxxx> wrote:
> 
>> On Wed, Jul 01, 2026 at 08:40:39AM +0200, 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 a generic spi,device-addr property to document this per-peripheral
>>> address. This property belongs in channel or sub-device nodes of
>>> peripherals that use this addressing scheme.
>>>
>>> Signed-off-by: Janani Sunil <janani.sunil@xxxxxxxxxx>
>>> ---
>>>  Documentation/devicetree/bindings/spi/spi-peripheral-props.yaml | 5 +++++
>>>  1 file changed, 5 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/spi/spi-peripheral-props.yaml b/Documentation/devicetree/bindings/spi/spi-peripheral-props.yaml
>>> index 880a9f624566..3774e8018355 100644
>>> --- a/Documentation/devicetree/bindings/spi/spi-peripheral-props.yaml
>>> +++ b/Documentation/devicetree/bindings/spi/spi-peripheral-props.yaml
>>> @@ -142,6 +142,11 @@ properties:
>>>      minItems: 2
>>>      maxItems: 4
>>>  
>>> +  spi,device-addr:  
>>
>> To match other generic spi properties, s/,/-/.
>>
>> However, you don't actually use this as a spi peripheral's property in
>> your device binding, so you've got your wires crossed here somewhere.
> 
> If we are going to make this generic (which I'm not against) I think
> it should also work for the case of multiple independent devices.
> So it can also be a top level device node spi property.
> 
> That kind of makes me wonder if we are better off having it always
> in the top level node, but allowing multiple values to represent
> sub devices under this.  That would leave figuring out mappings of which
> channels are on which device to the driver. The driver must know the
> mapping afterall.  For the example something like
> 
> 
> #include <dt-bindings/gpio/gpio.h>
> spi {
>     #address-cells = <1>;
>     #size-cells = <0>;
>     dac@0 {
>         compatible = "adi,ad5529r-16";
>         reg = <0>;
>         spi-max-frequency = <25000000>;
> 
>         spi-device-addreses = <0 3>
> ...
> 
>         #address-cells = <1>;
>         #size-cells = <0>;
> 
>         channel@0 {
>             reg = <0>;
>             adi,output-range-microvolt = <0 5000000>;
>         };
> 
>         channel@16 { #on second device using dev addr 3
>             reg = <16>;
>             adi,output-range-microvolt = <(-10000000) 10000000>;
>         };
>         channel@18 { #3rd channel on device using dev addr 3
>             reg = <18>;
>             adi,output-range-microvolt = <0 40000000>;
>         };
>     };
> };
> 
> Where devices are truely independent then you would have separate device
> nodes each with one entry in spi-device-addresses
> 
> I'm a bit dubious about putting this in the spi namespace though given
> it is not part of any standard specification.  Do we have any precedence
> for that sort of thing?

It seems like most SPI controllers/devices don't really follow any
standards, so I think there is plenty of precedence for a property
like this. It would be nice to see one or two more examples of SPI
peripherals with this feature though other than the one chip in
this series. Otherwise, I wouldn't try to make it a standard property.

I'm also in favor of making it an array and letting the device-specific
bindings decide what multiple devices with different addresses on the
same CS line means.

But... if we are leaving it up to devices to deal with the property rather
than the core SPI code, maybe it shouldn't be a standard SPI property.
Although, I suppose the core SPI code could parse the property and just
pass that information in the struct spi_device to let the device driver
do what it wants with it.

> 
> Jonathan
> 
>>
>> If it's a generic dac channel property (as you use it) it should be in
>> dac.yaml (or adc.yaml for the other device that I asked you to add it
>> for as proof of being generic), or it is a spi peripheral property and
>> needs to go into the dac node itself.
>>
>> pw-bot: changes-requested
>>
>>> +    $ref: /schemas/types.yaml#/definitions/uint32
>>> +    description:
>>> +      Device address used when multiple peripherals share a single chip select.
>>> +
>>>    st,spi-midi-ns:
>>>      deprecated: true
>>>      description: |
>>>
>>> -- 
>>> 2.43.0
>>>   
>