Il 13/02/2014 14:26, Alex David ha scritto:
After reading code, documentation and available things, I've been trying
to write something like a "virtio-i2c" : I wrote a virtio-i2c module for
my kernel (I used some examples from virtio-pci and virtio-console), it
seems that it created a "i2c-1" device in /dev,
My device that I launch with QEMU (-chardev
socket,path=/tmp/test0,server,nowait,id=bob -device
virtio-i2c,chardev=bob) doesn't seem to be recognized by the kernel
driver : my probe function doesn't run.
i2c is a bus, not directly a device. Do you want to pass an entire
adapter down to the guest? Or just a slave?
QEMU has i2c emulation but it is bus-based, so you need one device per
slave + 1 for the adapter. x86 already has an I2C bus (actually it's
SMBus) that you may be able to use. So you probably want something like
-object i2c-linux,file=/dev/i2c-1,id=i2c-backend
-device i2c-host,backend=i2c-backend,hostaddr=0x40,address=0x40
-device i2c-host,backend=i2c-backend,hostaddr=0x50,address=0x50
and so on. i2c-linux would be the object issuing ioctls to /dev/i2c-1,
multiplexing access to the device for all the i2c-host devices.
If the default I2C bus is not good, I suggest that you write QEMU code
to emulate an USB-I2C bridge, rather than write a virtio one. It is not
a performance-intensive path in all likelihood, and you won't have to
write driver code for the guest.
Another alternative is to support the kernel's I2C-over-parallel
interface. You can then write a character device backend that maps
/dev/i2c-1 read/write/ioctl to the parallel port interface that the
kernel expects use it with a parallel port device. It would be used
like this:
-chardev i2c-linux,file=/dev/i2c-1,id=i2c-backend
-device parallel,chrdev=i2c-backend
Paolo
