rpisense-fb not allocating /sys/graphics/fb* device

[mgreter]

Hi folks

I'm trying to use my sense hat with a raspberry pi 2 on a custom gentoo linux installation, but I cannot get the led matrix to work. What I got from reading the python sourcecode, it should allocate a framebuffer device for it, but I fail to get that device "allocated".

I'm using raspberrypi-sources-4.1.9999.ebuild (currently at d2b2388) with this config:

# cat .config | grep RPI
CONFIG_JOYSTICK_RPISENSE=m
CONFIG_TOUCHSCREEN_RPI_FT5406=m
CONFIG_MFD_RPISENSE_CORE=m
CONFIG_FB_RPISENSE=m
CONFIG_SND_BCM2708_SOC_RPI_DAC=m
CONFIG_SND_BCM2708_SOC_RPI_PROTO=m
CONFIG_LIRC_RPI=m

The module seems to load correctly

# modprobe rpisense-fb
# modprobe rpisense-js
# lsmod | grep rpi
rpisense_js             2431  0
rpisense_fb             3664  0
rpisense_core           2187  2 rpisense_fb,rpisense_js
fb_sys_fops             1149  1 rpisense_fb
syscopyarea             2949  1 rpisense_fb
sysfillrect             3339  1 rpisense_fb
sysimgblt               1961  1 rpisense_fb

I still only have one framebuffer device (I'd expect RPI-Sense FB):

# cat /sys/class/graphics/fb*/name
BCM2708 FB

The sense hat is showing the "rainbow" after the raspberry pi is powered up and I can see the sensors and the "rpisense" interface (I guess it's the one at 0x46):

# modprobe i2c-dev
# i2cdetect -y 1
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- UU 1c -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- 46 -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- 5c -- -- 5f
60: -- -- -- -- -- -- -- -- -- -- 6a -- -- -- -- --
70: -- -- -- -- -- -- -- --

My findings for future reference:

0x1c Magnetometer LSM9DS1
0x46 rpi-sense (ATtiny88?)
0x5c Pressure LPS25H
0x5f Humidity HTS221
0x6a Accelerometer LSM9DS1

I also don't get any messages in dmesg? I even tried to hack an early dev_info message into rpisense_fb_probe of drivers/video/fbdev/rpisense-fb.c, but I still don't see anything in dmesg!?

Any pointers what I might be doing wrong? I first tried to connect the sense hat only with the necessary pins (since I need to attach additional i2c breakouts), but I have it now directly connected, so that should not be the problem (unless I did some damage I'm not aware of in the experimental process).

I also tried to play with dtoverlay in /boot/config.txt and I am confused what this option actually does? I know the difference between builtin modules, initrd and "runtime" modules. Do I always need to add dtoverlay=rpi-sense or only if it is built into the kernel? I have put rpi-sense-overlay.dtb into /boot and /boot/overlays and the line in /boot/config.txt, but still got no framebuffer device? Do I have to compile them myself (I can get avr-gcc built but will probably take a day or two to compile). Or should it be ok if I downloaded it from the firmware repository?

Hope I got the right Bugtracker for this!
Any help is welcome! Thank you!

[XECDesign]

Sounds like everything should work. You shouldn't even need the dtoverlay parameter, since that should be loaded automatically from the EEPROM. I suspect you don't have a dt-enabled kernel. I don't see anything in that ebuild that would pass it through mkknlimg and i2cdetect doesn't show 'UU' on 0x46, suggesting that the device isn't instantiated.

[mgreter]

So any suggestions what I can do to get it "instantiated"? I would guess that i2cdetect should show UU once the device is used by a kernel module. The mkknlimg sounds interesting. Do I need such a step to create a kernel? I do think to have seen some instructions at some point regarding this.

Actually the ebuild only installs the sources into /usr/src/ and I only added some additional filesystems (btrfs) via make menuconfig (it internally runs make bcmrpi_defconfig once). I started with some 4.1.17 kernel and updated today to 4.1.18 (commit id as mentioned in the original post), then ran make olddefconfig.

I'm also not familiar what you mean by "dt-enabled" kernel. If you can point me to the config entry I will gladly provide that information. Thanks! I also wonder why I'm not able to get any message via dmesg?

p.s. to be clear, I install the kernel in this way:

make modules_install
cp -a arch/arm/boot/Image /boot/kernel7.img

[XECDesign]

Method 4 here https://www.kernel.org/doc/Documentation/i2c/instantiating-devices

Yup, mkknlimg is required for device tree to work properly.

If you're using that defconfig all the necessary kernel options are there, there's just a bit that mkknlimg tags on due to... reasons.

Instead of cp -a arch/arm/boot/Image /boot/kernel7.img, try scripts/mkknlimg arch/arm/boot/Image /boot/kernel7.img

But I'd point out that bcmrpi_defconfig should be kernel.img (pi 1 kernel), not kernel7.img (pi 2 kernel). The correct defconfig for kernel7.img would bcm2709_defconfig.

[mgreter]

Thanks! I will try that. I actually saw that error in the ebuild for bcm2709_defconfig once, and I thought I had incorporated it into my local ebuild. But I just checked and I still have bcmrpi_defconfig, so will rebuild a clean kernel with bcm2709_defconfig and apply my changes, then I'll try to use mkknlimg. Will report back this weekend! Really hope I can get this working! Thanks again!

[mgreter]

Just read your link and remembered that command from my ds1307 rtc and actually

echo rpisense-fb 0x46 > /sys/class/i2c-adapter/i2c-1/new_device
dmesg: i2c i2c-1: new_device: Instantiated device rpisense-fb at 0x46

But I still have no /sys/class/graphics/fb* device ...

[XECDesign]

Try rpisense-core instead of rpisense-fb

[mgreter]

It seems to give the same results. I do get a new "sys/i2c" directory. I hope I may be able to add some debug statements to the c code, so I can see why it does not load the device now I see something in dmesg.

ls -la /sys/class/i2c-adapter/i2c-1/1-0046/
total 0
-r--r--r-- 1 root root 4096 Sep 25 03:33 modalias
-r--r--r-- 1 root root 4096 Sep 25 03:33 name
lrwxrwxrwx 1 root root    0 Sep 25 03:33 subsystem -> ../../../../../bus/i2c
-rw-r--r-- 1 root root 4096 Sep 25 03:32 uevent

[mgreter]

Success! Got it working today. Seems I really was only missing scripts/mkknlimg arch/arm/boot/Image /boot/kernel7.img! Thanks @XECDesign for your help.

# cat /sys/class/graphics/fb*/name
BCM2708 FB
RPi-Sense FB