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

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Message-ID: <34e84bd2-381b-4f3e-99e1-92f7a878ed15@linux.dev>
Date: Thu, 23 Jan 2025 17:57:41 -0500
From: Sean Anderson <sean.anderson@...ux.dev>
To: Rob Herring <robh@...nel.org>
Cc: Michal Simek <michal.simek@....com>, Mark Brown <broonie@...nel.org>,
 linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org,
 Jinjie Ruan <ruanjinjie@...wei.com>, linux-arm-kernel@...ts.infradead.org,
 Amit Kumar Mahapatra <amit.kumar-mahapatra@....com>,
 Miquel Raynal <miquel.raynal@...tlin.com>, Conor Dooley
 <conor+dt@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 devicetree@...r.kernel.org
Subject: Re: [PATCH 1/5] dt-bindings: spi: zynqmp-qspi: Add reset

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@...ux.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 :)

> 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.

--Sean