linux-kernel - Re: [PATCH] iio: magnetometer: si7210: fix magnetic field measurement scale

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Message-ID: <20250203193920.stcb5mhrt4vgmbae@antoni-VivoBook-ASUSLaptop-X512FAY-K512FA>
Date: Mon, 3 Feb 2025 20:39:20 +0100
From: Antoni Pokusinski <apokusinski01@...il.com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: jic23@...nel.org, lars@...afoo.de, linux-kernel@...r.kernel.org,
	linux-iio@...r.kernel.org
Subject: Re: [PATCH] iio: magnetometer: si7210: fix magnetic field
 measurement scale

On Mon, Feb 03, 2025 at 11:26:27AM +0200, Andy Shevchenko wrote:
> On Sun, Feb 02, 2025 at 11:07:10AM +0100, Antoni Pokusinski wrote:
> > Applying the current scale value to the raw magnetic field measurements
> > gives the result in mT.
> > 
> > Fix the scale by increasing it 10 times, so that the final result after
> > applying the scale is in Gauss.
> 
> No objections against this change, just wondering since these are
> the ABI changes (correct?) how should we really handle them in case
> some of the user space stuff already relies on 'bad' values?
> 
> -- 
> With Best Regards,
> Andy Shevchenko
> 
> 

Just to clarify: yes, this patch makes the output values compliant to
ABI (Documentation/ABI/testing/sysfs-bus-iio). According to the ABI, the
output values for the magnetic field should be in Gauss, but during
the driver development I missed the fact that I return values in mT
instead... (1 Gauss = 0.1mT)

BTW I see that the patch cb29542a178f ("iio: magnetometer: si7210: add
driver for Si7210") is still on the "testing" branch only, so perhaps
it's still not too late to apply the fix?

Kind regards,
Antoni