Re: [PATCH 1/5] dt-bindings: iio: dac: ti,dac5571: Add DAC081C081 support

From: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Jonathan Cameron <jic23@kernel.org>, <devicetree@vger.kernel.org>,
	<imx@lists.linux.dev>, <linux-arm-kernel@lists.infradead.org>,
	"Trevor Zaharichuk" <trevor@au-zone.com>,
	Greg Lytle <greg@au-zone.com>,
	"Lars-Peter Clausen" <lars@metafoo.de>,
	Rob Herring <robh@kernel.org>,
	"Krzysztof Kozlowski" <krzysztof.kozlowski+dt@linaro.org>,
	Conor Dooley <conor+dt@kernel.org>,
	Sean Nyekjaer <sean@geanix.com>, <linux-iio@vger.kernel.org>
Subject: Re: [PATCH 1/5] dt-bindings: iio: dac: ti,dac5571: Add DAC081C081 support
Date: Tue, 26 Mar 2024 15:29:27 +0000	[thread overview]
Message-ID: <20240326152927.00006229@Huawei.com> (raw)
In-Reply-To: <20240325205641.GD23988@pendragon.ideasonboard.com>

On Mon, 25 Mar 2024 22:56:41 +0200
Laurent Pinchart <laurent.pinchart@ideasonboard.com> wrote:

> Hi Jonathan,
> 
> On Mon, Mar 25, 2024 at 08:48:57PM +0000, Jonathan Cameron wrote:
> > On Mon, 25 Mar 2024 22:32:41 +0200 Laurent Pinchart wrote:
> >   
> > > The DAC081C081 is a TI DAC whose software interface is compatible with
> > > the DAC5571. It is the 8-bit version of the DAC121C081, already
> > > supported by the DAC5571 bindings. Extends the bindings to support this
> > > chip.
> > > 
> > > Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>  
> > 
> > Hi Laurent,
> > 
> > Given it's a part number where no one is going to guess it is compatible
> > with the DAC5571 and that we don't have a history of fallback compatibles
> > I'm fine with this change, but just wanted to ask is a fallback compatible
> > useful to you to run with older kernels?
> > 
> > I should have noticed when Peter added the dac121c081. If we add a fallback
> > should do that one as well.  
> 
> I've indeed noticed that there should have been a fallback for
> dac121c081, but didn't stop to ponder why that wasn't the case, and just
> went along with the flow :-) I agree a fallback could be useful, which
> would then allow dropping patch 2/5 from this series (*). I can do so if
> you prefer.
> 
> * This is not entirely true. While the DAC1081C081 is largely compatible
> with the DAC5573, they have different values for one of the power-down
> resistors (2.5kΩ instead of 1kΩ if I recall correctly). To be completely
> accurate, the driver should report that. We could still use the fallback
> compatible, reporting the wrong power-down resistor value.
> 

Hmm - Would anyone really care about that value being wrong?
I think perhaps that's just about significant enough that maybe a fallback
compatible doesn't make sense here.

Jonathan

> > > ---
> > >  Documentation/devicetree/bindings/iio/dac/ti,dac5571.yaml | 1 +
> > >  1 file changed, 1 insertion(+)
> > > 
> > > diff --git a/Documentation/devicetree/bindings/iio/dac/ti,dac5571.yaml b/Documentation/devicetree/bindings/iio/dac/ti,dac5571.yaml
> > > index 79da0323c327..e59db861e2eb 100644
> > > --- a/Documentation/devicetree/bindings/iio/dac/ti,dac5571.yaml
> > > +++ b/Documentation/devicetree/bindings/iio/dac/ti,dac5571.yaml
> > > @@ -21,6 +21,7 @@ properties:
> > >        - ti,dac5573
> > >        - ti,dac6573
> > >        - ti,dac7573
> > > +      - ti,dac081c081
> > >        - ti,dac121c081
> > >  
> > >    reg:  
> 

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