iMX287 LRADC internal temperature giving 0 Kelvin

[sam_jaeschke]

I'm using Linux 4.8.17 from this commit: GitHub - Freescale/linux-fslc at 35ef7950aaf7caa28afae35160bda0734ecfeba7 

My device tree has this:

#include "imx28.dtsi"

&lradc {
   status = "okay";
   fsl,ave-ctrl = <4>;
   fsl,ave-delay = <2>;
   fsl,settling = <10>;
};

Using sysfs to access the LRADC's temperature channel:

# cat /sys/devices/soc0/80000000.apb/80040000.apbx/80050000.lradc/iio\:device0/in_temp8_raw
2  

It gives values only -2 to 2 (with multiple runs).

The manual has relevant section 38.2.2 Internal Die Temperature Sensing.

https://www.nxp.com/docs/en/reference-manual/MCIMX28RM.pdf 

The mxs-lradc driver has code that looks like it matches the manual description quite well.

linux-fslc/mxs-lradc.c at 35ef7950aaf7caa28afae35160bda0734ecfeba7 · Freescale/linux-fslc · GitHub 

The sysfs scale is: 0.253000

The sysfs offset is: -1079.644268 (to convert Kelvin to C)

The sysfs raw output multiplied by the scale should be in Kelvin, so it is reading around 0 Kelvin.

It seems like the raw should be reading around 1200 or more: (1200 - 1079.6) * 0.253 = 30.46C, which is low but in the right region.

The mxs-lradc driver looks like it is setting the TEMPSENSE flag correctly at the beginning.

Is this a known problem? What might be the cause?

[igorpadykov]

Hi Sam

Linux 4.8.17 is not supported by nxp and its issues can be posted on kernel mail list.

There were no known issues with i.MX28 lradc driver and one can test it with older offical nxp releases

linux-2.6-imx.git - Freescale i.MX Linux Tree 

baremetal OBDS

i.MX28 Evaluation Kit|NXP 

Best regards
igor
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[sam_jaeschke]

Thanks Igor, I will check out the older code.

Linux 3.0 was released 7 years ago, so it seems quite a backwards step to have to go back to the 2.6 kernel.

However, I see here that linux-imx repo is "Linux Kernel provided and supported by NXP with focus on i.MX Family Reference Boards. It includes support for many IPs such as GPU, VPU and IPU."

http://git.yoctoproject.org/cgit/cgit.cgi/meta-freescale/tree/recipes-kernel/linux/linux-imx_4.9.88....

That would seem to have an officially supported lradc driver, right? Is this a better choice to use?

And linux-fslc is described as: "Linux kernel based on mainline kernel used by FSL Community BSP in order to provide support for some backported features and fixes, or because it was applied in linux-next and takes some time to become part of a stable version, or because it is not applicable for upstreaming."

linux-fslc_4.17.bb\linux\recipes-kernel - meta-freescale - Layer containing NXP hardware support met... 

And for completeness, there is also linux-fslc-imx: "Linux kernel based on NXP 4.9.11-1.0.0 GA release, used by FSL Community BSP in order to provide support for i.MX based platforms and include official Linux kernel stable updates, backported features and fixes coming from the vendors, kernel community or FSL Community itself."

linux-fslc-imx_4.9-1.0.x.bb\linux\recipes-kernel - meta-freescale - Layer containing NXP hardware su... 

Also, I can't find any mention of LRADC channel 8 or 9, or TEMPSENSE flag in the On Board Diagnostic Suite code, so I don't think that will help solve it.

[igorpadykov]

Hi Sam

please check description of differencies between community "linux-fslc" bsps and official nxp bsps "linux-imx":

difference between Yocto Community BSP and Freescale BSP Release 

[meta-freescale] Issue with freescale git server at git.freescale.com 

official nxp bsps are described on below link (there is no i.MX28 support)

i.MX Software|NXP 

Best regards
igor

[sam_jaeschke]

Or to put this another way, can you point me to a version of the mxs-lradc driver which is supported and is known to work well?

[igorpadykov]

Hi Sam

please refer to Chapter 18 Touch Screen and ADC Drivers attached L2.6.35 Linux Manual.

Old NXP linux bsps can be supported using NXP Professional Services

NXP Professional Services|NXP 

Questions for community "linux-fslc" releases also can be posted on meta-fsl-arm mailing list
https://lists.yoctoproject.org/listinfo/meta-freescale

Best regards
igor

[sam_jaeschke]

Ah, right, cheers.

Oops, I found I was searching on master branch instead of imx_2.6.35_11.09.01 on linux-2.6-imx...

I found the lradc driver here, which is written differently, but seems to follow about the same.

linux-2.6-imx.git - Freescale i.MX Linux Tree 

Thanks for your help.

[sam_jaeschke]

Okay, thanks. I am not using an evaluation board, so it is clear from the table that I am interested in the FSL Community BSP.

But with the linux-imx, is there one release version (effectively) for the evaluation board, then that just stays stagnant, and the newer evaluation board comes along and gets a newer kernel version and gets released and stays stagnant, then another board comes along.... is that how it works? So pulling the latest linux-imx and using it for an older evaluation board/system won't necessarily be supported? Is that how it works? Otherwise, why not use linux-imx, since it's kernel 4.9?

Anyway, with your link:
linux-2.6-imx.git - Freescale i.MX Linux Tree 

I can't find the lradc driver....

> find . -name "*lradc*"
>

Did the driver have another name other than mxs-lradc? There are other mxs drivers:

> find . -name "*mxs*"
./sound/soc/mxs
./sound/soc/mxs/mxs-sgtl5000.c
./sound/soc/mxs/mxs-pcm.c
./sound/soc/mxs/mxs-saif.c
./sound/soc/mxs/mxs-saif.h
./sound/soc/mxs/mxs-pcm.h
./arch/arm/mach-imx/eukrea_mbimxsd35-baseboard.c
./arch/arm/mach-imx/eukrea_mbimxsd25-baseboard.c
./arch/arm/configs/mxs_defconfig
./arch/arm/mach-mxs
./arch/arm/mach-mxs/include/mach/mxs.h
./arch/arm/mach-mxs/include/mach/mxsfb.h
./arch/arm/mach-mxs/devices/platform-mxs-mmc.c
./arch/arm/mach-mxs/devices/platform-mxs-i2c.c
./arch/arm/mach-mxs/devices/platform-gpio-mxs.c
./arch/arm/mach-mxs/devices/platform-mxs-saif.c
./arch/arm/mach-mxs/devices/platform-mxs-pwm.c
./arch/arm/mach-mxs/devices/platform-mxsfb.c
./arch/arm/mach-mx5/eukrea_mbimxsd-baseboard.c
./drivers/dma/mxs-dma.c
./drivers/video/mxsfb.c
./drivers/mmc/host/mxs-mmc.c
./drivers/tty/serial/mxs-auart.c
./drivers/tty/mxser.h
./drivers/tty/mxser.c
./drivers/gpio/gpio-mxs.c
./drivers/i2c/busses/i2c-mxs.c