RPI4/8GB i2c not working?

[Klaus Küchemann]

root at generic:~ # i2c -f /dev/iic0 -s -v
dev: /dev/iic0, addr: 0x40100401, r/w: r, offset: 0x00, width: 8, count: 1
Hardware may not support START/STOP scanning; trying less-reliable read method.

——

So the device is there ! ....

root at generic:~ # ktrace -t+ i2c -s -f /dev/iic0

root at generic:~ # kdump
....
1287 i2c      RET   open 3
  1287 i2c      CALL  read(0x3,0x4027cc18,0x80)
  1287 i2c      GIO   fd 3 read 128 bytes
       0x0000 4568 6e74 0100 0000 8000 0000 d500 0000  |Ehnt............|
       0x0010 0000 0000 d400 0000 0000 0000 0000 0000  |................|
       0x0020 0000 0000 0000 0000 0000 0000 0000 0000  |................|
       0x0030 0000 0000 0000 0000 0000 0000 0000 0000  |................|
       0x0040 0000 0000 0000 0000 0000 0000 0000 0000  |................|
       0x0050 0000 0000 0000 0000 0000 0000 0000 0000  |................|
       0x0060 0000 0000 0000 0000 0000 0000 0000 0000  |................|
       0x0070 0000 0000 0000 0000 0000 0000 0000 0000  |................|

—

successful GIO   fd 3 read looks quite good working !…


But then loops in the end :

1287 i2c      RET   ioctl -1 errno 35 Resource temporarily unavailable
  1287 i2c      CALL  ioctl(0x3,I2CRSTCARD,0xffffffffea70)
  1287 i2c      RET   ioctl 0
  1287 i2c      CALL  ioctl(0x3,I2CRDWR,0xffffffffe998)
  1287 i2c      RET   ioctl -1 errno 35 Resource temporarily unavailable
  1287 i2c      CALL  ioctl(0x3,I2CRSTCARD,0xffffffffea70)


since I don't have an i2c-gadget to test at the moment , can't say which device exactly 
supports START/STOP scanning and which not.

Also possibly some things cood depend on loaded overlays/config.txt 
and which corresponding GPIO-pins are configured 

K.