Re: [PATCH v3 36/47] mfd: ti_am335x_tscadc: Support the correctly spelled DT property

From: Lee Jones <lee.jones@linaro.org>
To: Miquel Raynal <miquel.raynal@bootlin.com>
Cc: Jonathan Cameron <jic23@kernel.org>,
	Lars-Peter Clausen <lars@metafoo.de>,
	Peter Meerwald-Stadler <pmeerw@pmeerw.net>,
	Rob Herring <robh+dt@kernel.org>,
	Dmitry Torokhov <dmitry.torokhov@gmail.com>,
	bcousson@baylibre.com, Tony Lindgren <tony@atomide.com>,
	linux-iio@vger.kernel.org, devicetree@vger.kernel.org,
	linux-omap@vger.kernel.org,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
	Vignesh Raghavendra <vigneshr@ti.com>,
	Lokesh Vutla <lokeshvutla@ti.com>,
	Tero Kristo <kristo@kernel.org>,
	Ryan Barnett <ryan.barnett@collins.com>,
	Grygorii Strashko <grygorii.strashko@ti.com>,
	Jason Reeder <jreeder@ti.com>,
	Jonathan Cameron <Jonathan.Cameron@huawei.com>
Subject: Re: [PATCH v3 36/47] mfd: ti_am335x_tscadc: Support the correctly spelled DT property
Date: Mon, 27 Sep 2021 09:09:32 +0100	[thread overview]
Message-ID: <YVF8PDl54lpUc+6S@google.com> (raw)
In-Reply-To: <20210923113312.14fc9027@xps13>

On Thu, 23 Sep 2021, Miquel Raynal wrote:

> Hi Lee,
> 
> lee.jones@linaro.org wrote on Thu, 23 Sep 2021 10:11:13 +0100:
> 
> > On Thu, 23 Sep 2021, Miquel Raynal wrote:
> > 
> > > Hi Lee,
> > > 
> > > lee.jones@linaro.org wrote on Wed, 22 Sep 2021 16:57:10 +0100:
> > >   
> > > > On Wed, 15 Sep 2021, Miquel Raynal wrote:
> > > >   
> > > > > There was in the past a typo in the coordinate readouts property. The
> > > > > bindings have been updated, the touchscreen driver as well and now
> > > > > supports both. However, the MFD driver that is in charge of verifying
> > > > > the validity of the property only checks the bogus one. Add support for
> > > > > the correctly spelled DT property.
> > > > > 
> > > > > Fixes: c9aeb249bf72 ("Input: ti_am335x_tsc - fix spelling mistake in TSC/ADC DT binding")
> > > > > Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
> > > > > Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > > > > ---
> > > > >  drivers/mfd/ti_am335x_tscadc.c | 8 +++++++-
> > > > >  1 file changed, 7 insertions(+), 1 deletion(-)
> > > > > 
> > > > > diff --git a/drivers/mfd/ti_am335x_tscadc.c b/drivers/mfd/ti_am335x_tscadc.c
> > > > > index 155a8ed879b3..aa46ed669016 100644
> > > > > --- a/drivers/mfd/ti_am335x_tscadc.c
> > > > > +++ b/drivers/mfd/ti_am335x_tscadc.c
> > > > > @@ -144,8 +144,14 @@ static	int ti_tscadc_probe(struct platform_device *pdev)
> > > > >  	if (tscadc->data->has_tsc) {
> > > > >  		node = of_get_child_by_name(pdev->dev.of_node, "tsc");
> > > > >  		of_property_read_u32(node, "ti,wires", &tscmag_wires);
> > > > > -		of_property_read_u32(node, "ti,coordiante-readouts", &readouts);
> > > > > +		err = of_property_read_u32(node, "ti,coordinate-readouts",
> > > > > +					   &readouts);
> > > > > +		if (err < 0)
> > > > > +			of_property_read_u32(node, "ti,coordiante-readouts",
> > > > > +					     &readouts);
> > > > > +    
> > > > 
> > > > How long are you proposing that we support this churn?  
> > > 
> > > Well, I am not proposing anything, I am just "fixing" the driver so
> > > that it fits the bindings :) Given the fact that at the end of this
> > > series there is a patch that changes the "coordiante" typo to
> > > "coordinate" in a device tree source file, I believe it is still too
> > > soon...  
> > 
> > If this is something you're changing in this set, please reconsider.
> > 
> > I'd rather have a slightly misspelled documented property than being
> > forced to support 2 for any length of time.
> 
> I am not suggesting anything here:
> - "coordiante" was introduced back in 2014.
> - "coordinate" was introduced shortly later.
> - "coordiante" was considered part of the "stable API" back in 2014 and
>   even though the right spelling got introduced very shortly after, DT
>   stability rules wanted us to support it forever.
> - The touchscreen driver has immediately be fixed to support both but
>   not the MFD driver, and this does not make any sense!
> 
> We *should* either support only one property (1) or support both in the
> two drivers (2), but supporting the two in one driver and supporting
> only one in the other one does not make any sense (given the fact that
> these two drives are tied together, the touchscreen driver does not
> exist without the MFD driver). That is what I am fixing here.
> 
> Is #1 valid? Theoretically it's the best scenario. In practice it is
> not (yet) possible because the two versions are still used in the
> mainline device trees:
> $ git grep coordiante-readouts -- arch/arm/boot/dts/ | wc -l
> 1
> $ git grep coordinate-readouts -- arch/arm/boot/dts/ | wc -l
> 5
> 
> So in this series I am fixing the MFD driver to be sure it handles
> correctly the correctly spelled DT property which is used by 5 boards
> since at least 6 years and I am also updating the remaining DT to use
> the correctly spelled property as well.
> 
> I suppose we could propose to drop support for the "coordiante"
> version of that property in a few years but if we decide to do it right
> now we're definitely gonna break users.

It's a shame that the misspelled one is still in use.  If they were
all changed over at the start, there would be a strong case for
dropping support for it.

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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