Re: [BUG] iio: imu: inv_icm42600: read temperature, Invalid Argument

[Jonathan Cameron <Jonathan.Cameron@huawei.com>]

On Mon, 7 Jul 2025 18:13:33 +0000
Jean-Baptiste Maneyrol <Jean-Baptiste.Maneyrol@tdk.com> wrote:

> >Hi,
> >
> >I'm having some weird issues with reading the temperature of the icm42605.
> >Kernel version: 6.16.0-rc5
> >
> ># cat /sys/bus/iio/devices/iio:device2/name
> >icm42605-accel
> >
> >When reading the temperature I get:
> ># cat /sys/bus/iio/devices/iio:device2/in_temp_raw
> >cat: read error: Invalid argument
> >
> >But if I read from the accelerometer first, I will go better:
> ># cat /sys/bus/iio/devices/iio:device2/in_accel_x_raw
> >-378
> ># cat /sys/bus/iio/devices/iio:device2/in_temp_raw
> >600
> >
> >Then after "some" time, I re-read the temperature I recieve
> >"Invalid argument" again.
> >
> >I have traced the -EINVAL to inv_icm42600_temp_read() because I receive
> >INV_ICM42600_DATA_INVALID.
> >
> >Register dump diff:
> >--- invalid-read
> >+++ ok-read
> >@@ -10,14 +10,14 @@
> > 0x1a = 0x00000010
> > 0x1b = 0x00000000
> > 0x1c = 0x00000000
> >-0x1d = 0x00000080
> >-0x1e = 0x00000000
> >-0x1f = 0x00000080
> >-0x20 = 0x00000000
> >-0x21 = 0x00000080
> >-0x22 = 0x00000000
> >-0x23 = 0x00000080
> >-0x24 = 0x00000000
> >+0x1d = 0x00000002
> >+0x1e = 0x00000038
> >+0x1f = 0x000000fe
> >+0x20 = 0x00000085
> >+0x21 = 0x000000fe
> >+0x22 = 0x000000df
> >+0x23 = 0x000000f8
> >+0x24 = 0x0000003a
> > 0x25 = 0x00000080
> > 0x26 = 0x00000000
> > 0x27 = 0x00000080
> >@@ -26,7 +26,7 @@
> > 0x2a = 0x00000000
> > 0x2b = 0x00000000
> > 0x2c = 0x00000000
> >-0x2d = 0x00000000
> >+0x2d = 0x00000008
> > 0x2e = 0x00000000
> > 0x2f = 0x00000000
> > 0x30 = 0x000000ff
> >@@ -59,11 +59,11 @@
> > 0x4b = 0x00000000
> > 0x4c = 0x00000032
> > 0x4d = 0x00000099
> >-0x4e = 0x00000000
> >+0x4e = 0x00000002
> > 0x4f = 0x00000009
> > 0x50 = 0x00000009
> > 0x51 = 0x00000016
> >-0x52 = 0x00000000
> >+0x52 = 0x00000060
> > 0x53 = 0x0000000d
> > 0x54 = 0x00000031
> > 0x55 = 0x00000000
> >
> >Will the iio core retry a read? If the -EINVAL is returned,
> >inv_icm42600_accel_read_raw() is call once more.
> >
> >One more thing...
> >When I'm removing the module, the kernel prints this:
> >inv-icm42600-i2c 1-0068: Runtime PM usage count underflow!
> >
> >I will continue investigate this
> >Br,
> >Sean  
> 
> Hello Sean,
> 
> this is expected behavior since the temperature returned is not the external
> temperature but the temperature of the mechanical component (MEMS). It will
> only work if the chip is on, meaning accelerometer and/or gyroscope is on.
> 
> That's why you can get temperature after reading accel data since it is
> turning the chip. But after a short while autosuspend is putting the chip
> back off and you cannot read temperature anymore.
> 
> You need to turn one sensor continuously on with a buffer, and then you can
> read temperature all the time since the chip is running.
> 
> Temperature data are here only to do temperature compensation of the accel
> and gyro data.

That is rather non-intuitive behavior.  Could we make a read of the temperature
channel turn on one of the components?  Given expected use case it shouldn't commonly
happen but if not too horrendous to implement it would be better to avoid the error
seen here.
 
> 
> Thanks,
> JB