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Date: Fri, 24 Apr 2026 11:48:18 +0100
From: Jonathan Cameron <jic23@kernel.org>
To: Andy Shevchenko <andriy.shevchenko@intel.com>
Cc: Nikhil Gautam <nikhilgtr@gmail.com>, linux-iio@vger.kernel.org,
 dlechner@baylibre.com, nuno.sa@analog.com, andy@kernel.org,
 linux-kernel@vger.kernel.org
Subject: Re: [RFC] iio: magnetometer: mlx90393 - regmap vs command-based
 access
Message-ID: <20260424114818.1290b029@jic23-huawei>
In-Reply-To: <aepaWzVfgRFlau6L@ashevche-desk.local>
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On Thu, 23 Apr 2026 20:43:55 +0300
Andy Shevchenko <andriy.shevchenko@intel.com> wrote:

> On Thu, Apr 23, 2026 at 05:55:35PM +0530, Nikhil Gautam wrote:
> > 
> > Apologies for missing a few details in the previous mail.
> > 
> > The MLX90393 supports both I2C and SPI interfaces.
> > 
> > Commands include, for example:
> > - SM (Start Measurement)
> > - RM (Read Measurement)
> > - RR (Read Register)
> > 
> > Given this command-oriented interface over both I2C and SPI,
> > I wanted to confirm whether a custom command abstraction layer
> > would still be the preferred approach instead of regmap.  
> 
> I found only 4 drivers for this vendor in the kernel and they seem
> either register based or eeprom based. Perhaps the latter is the
> case here? Have you checked existing implementations?
> 

If it doesn't match up with an existing case.

I took a look at the datasheet and this is a weird mix
of a register driven and command driven device.  As such you could
do regmap for the registers, buy you'd need to bypass that for
the command only stuff.  I don't think it's worth the mess of
creating some virtual registers to deal with the commands.

Hence I think in this particular case regmap doesn't look suitable
and a custom bus abstraction layer makes sense.  Some of that is going
to look regmap like, but with some other callbacks as well.

Jonathan