Marc Dietrich wrote: > the HW I'm using (tegra) can be configured to act as a slave. This function is > needed to communicate with an embedded controller (which is the master). I > like to know if this slave function can/should be implemented in the > i2c/busses/i2c-tegra.c driver or better outside, e.g. in the driver for the > embedded controller. Do you need to implement a slave for write-only or also read messages? > I haven't found any other hw so far which has this function and it seems that > the i2c layer does not provide any interface for the communication with a > master. In fact, the Freescale's MPC8xxx I2C controllers are also capable of slave operation. I've implemented it, and it's working fine. Please find attached a patch against 2.6.35. drivers/i2c/busses/i2c-mpc.c | 79 +++++++++++++++++++++++++++++++++++++++++-- drivers/i2c/i2c-dev.c | 8 +++- include/linux/i2c.h | 1 3 files changed, 84 insertions(+), 4 deletions(-) The proposal sent last year[1] relies on a generic API extension. << The i2c-dev subsystem is extended with a new flag I2C_M_SLAVE. Basically, a struct i2c_msg holding flag I2C_M_SLAVE will wait in slave mode for a write request on specified target address, and will report the received content to the user-land application. An example of driver implementation has been done for i2c-mpc. There's no support for read request yet, and I'm wondering whether it would make sense. The patch has been tested on powerpc MPC8313E. Note: the present i2c-mpc implementation is RFC and may be improved, esp. regarding current timing issues. [...] Talking about i2c-dev, does the I2C_M_SLAVE flag is the appropriate way of modelling the API extension? Is there any interest for this extension to be accepted in the linux kernel? >> [1] http://thread.gmane.org/gmane.linux.drivers.i2c/6417 Until now, I have no good proposal for the read request. It should be doable to pass a static array and let the kernel read from it, but I see no easy way to have a user task respond with compute-as-you-go. Still, the write message is satisfactory for my use case. Comments welcome. -- Stephane PS: sorry about my broken MUA, it's about to be changed in the coming weeks, as well as my e-mail address.
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mpc-i2c-slave.patch
Description: mpc-i2c-slave.patch
