Re: [PATCH] iio: acpi: Accept comma separated values in ROTM strings

[Jonathan Cameron <jic23@kernel.org>]

On Mon, 12 Oct 2026 23:55:49 +0300
Andy Shevchenko <andriy.shevchenko@intel.com> wrote:

> On Mon, Oct 12, 2026 at 03:41:44PM +0800, Yu-Hsiang Tseng wrote:
> > The ROTM method of the MXC6655 accelerometer on the Higole F9B, an
> > Alder Lake-N handheld (AMI BIOS F9D_16G_P800217, DMI strings are all
> > "Default string"), separates the values with a comma and a space:
> > 
> > 	Method (ROTM, 0, NotSerialized)
> > 	{
> > 	    Name (SBUF, Package (0x03)
> > 	    {
> > 	        "-1, 0, 0",
> > 	        "0, 1, 0",
> > 	        "0, 0, 1"
> > 	    })
> > 	    Return (SBUF)
> > 	}
> > 
> > iio_read_acpi_mount_matrix() only accepts the space separated form used
> > in Microsoft's example ("0 1 0"). It rejects this matrix and mxc4005
> > falls back to the identity matrix:
> > 
> > 	mxc4005 i2c-MXC6655:00: Incorrect ACPI mount matrix string format
> > 	mxc4005 i2c-MXC6655:00: mounting matrix not found: using identity...
> > 
> > With the X axis not inverted, iio-sensor-proxy reports left-up when the
> > device is held right-up and vice versa, so the desktop turns the
> > picture upside down whenever the handheld is held in landscape.
> > 
> > It is not the only BIOS written this way. The BOSC0200 on the AYANEO
> > Air Plus uses commas in its ROMS method as well, with a space before
> > one of them, and its ROMK method has "1, 0,0":
> > 
> > 	Method (ROMS, 0, NotSerialized)
> > 	{
> > 	    Name (SBUF, Package (0x03)
> > 	    {
> > 	        "-1, 0, 0",
> > 	        "0, -1 , 0",
> > 	        "0, 0, -1"
> > 	    })
> > 	    Return (SBUF)
> > 	}
> > 
> > The kernel's sscanf() does not support '%*[', so there is no clean way
> > to take both separators in a single format string. That leaves either
> > a second sscanf() call with a comma format, or normalizing the
> > separator first. Do the latter: turn the commas into spaces before
> > parsing, so the existing "%d %d %d" format, which already takes any
> > amount of white space around the values, keeps working unchanged. The
> > strings live in the buffer acpi_evaluate_object() allocated for us, so
> > they can be modified in place.
> > 
> > With this change in_accel_mount_matrix on the Higole F9B reads
> > "-1, 0, 0; 0, 1, 0; 0, 0, 1" and, with no udev hwdb override, the
> > desktop rotates correctly in all four orientations. The AYANEO Air
> > Plus was not tested; systemd's hwdb has an entry for it, which
> > iio-sensor-proxy prefers over the kernel's matrix.  
> 
> Makes sense, and fix is neat.
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
> 
Hmm. I debated dropping the stable tag, but meh, it's trivial and
makes stuff work that didn't before.

So applied to the fixes-togreg branch of iio.git keeping that tag.

I'll be rebasing that on rc1 once available before sending a pull
request.

Thanks,

Jonathan