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Date: Mon, 17 Feb 2014 17:11:34 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] Fwd: Trying to write a new device / virtio-i2c ?
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To: Alex David <alex.daerf@gmail.com>
Cc: qemu-devel <qemu-devel@nongnu.org>

Il 17/02/2014 16:33, Alex David ha scritto:
>     If you need more than one bus, you need a new device exposing the
>     I2C bus, besides the new sensor devices.  USB-I2C could be one such
>     device.
>
> So let me see if I understood well. USB-I2C (host QEMU device) seems a
> good idea, I could normally do : qemu-system-i386 -device
> usb-I2c,chardev=foo -device usb-i2c,chardev=bar -chardev
> socket,path=/tmp/test0,server,nowait,id=foo -chardev
> socket,path=/tmp/test1,server,nowait,id=bar.

Almost. For QOM:

     -device usb-i2c,id=usb-i2c-0
     -device i2c-my-sensor,address=0x48,bus=usb-i2c-0.0

For chardev:

     -device usb-i2c,id=usb-i2c-0
     -chardev socket,path=/tmp/test0,server,nowait,id=chr-foo-0
     -device i2c-my-sensor,address=0x48,bus=usb-i2c-0.0,chardev=chr-foo-0

Repeat for the other buses, replacing -0 with -1 and -2.

> I need a "USB-I2C guest kernel driver" that would register a bus (i2c-1
> for chardev foo, i2c-2 for chardev bar etc...), I guess ?

It exists already, drivers/i2c/busses/i2c-tiny-usb.c.

Paolo