linux-kernel - Re: [PATCH 2/2] drivers: iio: accel adxl312 and adxl314 support

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Date:   Tue, 16 Aug 2022 13:44:33 +0100
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
CC:     George Mois <george.mois@...log.com>, <jic23@...nel.org>,
        <robh+dt@...nel.org>, <krzysztof.kozlowski+dt@...aro.org>,
        <linux-iio@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <lucas.p.stankus@...il.com>
Subject: Re: [PATCH 2/2] drivers: iio: accel adxl312 and adxl314 support

On Tue, 16 Aug 2022 14:16:13 +0300
Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org> wrote:

> On 16/08/2022 13:28, George Mois wrote:
> > ADXL312 and ADXL314 are small, thin, low power, 3-axis accelerometers
> > with high resolution (13-bit) measurement up to +/-12 g and +/- 200 g
> > respectively.
> >   
> 
> Thank you for your patch. There is something to discuss/improve.
> 
> >  
> >  static const struct spi_device_id adxl313_spi_id[] = {
> > -	{ "adxl313" },
> > +	{ "adxl312", ADXL312 },
> > +	{ "adxl313", ADXL313 },
> > +	{ "adxl314", ADXL314 },
> >  	{ }
> >  };
> >  
> >  MODULE_DEVICE_TABLE(spi, adxl313_spi_id);
> >  
> >  static const struct of_device_id adxl313_of_match[] = {
> > +	{ .compatible = "adi,adxl312" },
> >  	{ .compatible = "adi,adxl313" },
> > +	{ .compatible = "adi,adxl314" },  
> 
> You miss here driver data. I don't remember which driver matching takes
> precedence (especially in various cases like DT platforms with device
> instantiated by MFD), but for consistency I think both device id tables
> should have same driver data.

You can set it up to try device_get_match_data() first then fallback
to the adxl313_spi_id[] table but there isn't a nice 'standard' way to
do it.

If that isn't done, then IIRC the match is against the compatible with
the vendor ID dropped and the table used is the spi_device_id one.
Which is just annoyingly complex and relies on the strings matching.

In the ideal world the spi_device_id table would go away but there are
still a few users (greybus - I think + remaining board files).
So for now something like

a = device_get_match_data(dev);
if (!a)
	a = &adxl31x_spi_regmap_config[id->data];

Provides a good way of ensuring the id tables don't need to remain
in sync.

Jonathan


> 
> 
> Best regards,
> Krzysztof