Re: [PATCH 1/5] dt-bindings: spi: zynqmp-qspi: Add reset

Michal Simek
2025-01-24T09:06:19Z

On 1/23/25 23:57, Sean Anderson wrote:
> On 1/23/25 17:45, Rob Herring wrote:
>> On Fri, Jan 17, 2025 at 11:12:15AM -0500, Sean Anderson wrote:
>>> On 1/17/25 02:14, Michal Simek wrote:
>>>>
>>>>
>>>> On 1/16/25 23:55, Sean Anderson wrote:
>>>>> Add a reset to help recover from cancelled operations.
>>>>>
>>>>> Signed-off-by: Sean Anderson <sean.anderson@linux.dev>
>>>>> ---
>>>>>
>>>>> Documentation/devicetree/bindings/spi/spi-zynqmp-qspi.yaml | 6 ++++++
>>>>> 1 file changed, 6 insertions(+)
>>>>>
>>>>> diff --git a/Documentation/devicetree/bindings/spi/spi-zynqmp-qspi.yaml b/Documentation/devicetree/bindings/spi/spi-zynqmp-qspi.yaml
>>>>> index 04d4d3b4916d..901e15fcce2d 100644
>>>>> --- a/Documentation/devicetree/bindings/spi/spi-zynqmp-qspi.yaml
>>>>> +++ b/Documentation/devicetree/bindings/spi/spi-zynqmp-qspi.yaml
>>>>> @@ -36,12 +36,16 @@ properties:
>>>>> power-domains:
>>>>> maxItems: 1
>>>>> + resets:
>>>>> + maxItems: 1
>>>>> +
>>>>> required:
>>>>> - compatible
>>>>> - reg
>>>>> - interrupts
>>>>> - clock-names
>>>>> - clocks
>>>>> + - resets
>>>>
>>>> In 2/5 you are calling devm_reset_control_get_optional_exclusive() that's why I expect reset is not really required property.
>>>
>>> It's optional for the driver for backwards compatibility. But for the
>>> devicetree we make it mandatory since it should be included in all new
>>> devicetrees.
>>
>> Generally, we discourage new required properties as that's an ABI
>> change. The exception is really when optional was a mistake. That's
>> arguably the case here if the h/w always has a reset.
>
> This device has a reset on ZynqMP and Versal.
>
> The driver still considers this property optional, so it's not an ABI break.
> But I made it required in the schema to help out the folks at AMD when they
> get around to upstreaming the Versal devicetree :)

Pretty much every IP block has hardware reset wired. It is just user decision if
that reset is going to be handled or if low level firmware allows to handle it.

The same logic applies to clocks too.

>> Unfortunately, there's not a way to distinguish 'required' from
>> 'required for new users'.
>
> I will add a note to the commit message about this situation.

Again even new users don't need to have an access to this feature.
Not sure what's the right way to go here but in our arm64 based chip reset is
provided via firmware interface and I have no issue to say we are expecting
reset property to be present but it is up to firmware implementation if a reset
is actually happening on HW level.

Thanks,
Michal