CODEWITHSUNDEEP
linuxlinux-kernellinux-device-driveri2c
Paul DeRocco
Paul DeRocco

Reputation: 413

Linux: access i2c device within board_init function

(iMX6 SOC running Linux 3.0)

I need to run a few I2C transactions in my board_init function. I tried calling i2c_get_adapter, then i2c_transfer, those being available in kernel mode, but i2c_get_adapter returns NULL. It's already called imx6q_add_imx_i2c, which is a wrapper around platform_device_register_full, but that isn't enough.

I can manipulate GPIO in board_init by calling gpio_request to obtain access, and gpio_free at the end. Is there something analogous to those functions for i2c?

--- added details ---

I've got a LAN9500A USB 100Base-T Ethernet MAC connected to a LAN9303 3-port switch with a virtual PHY. The MAC has a GPIO reset line that has to be turned off before it will spring to life and enumerate on the USB. That's done in board_init because it's completely nonstandard, so we don't want to patch the stock driver to manipulate some GPIO that's not part of the device.

The problem I'm having is that even though the MAC is permanently attached to the VPHY, it's not noticing it's connected, and an "ip link show eth1" command shows NO-CARRIER. I found I can kickstart it by unmasking the VPHY's Device Ready interrupt via I2C, but I also have to mask it immediately, or I get infinite interrupts. That's not the right solution, but Microchip has been no help in showing me a better way. But we don't want to patch the MAC driver with code to fiddle with the PHY.

There is no PHY driver for this part, and the MII interface to the VPHY doesn't include any interrupt-related registers, so it must be done through I2C. Writing a PHY driver just to flip a bit on and off once seems a lot of trouble, especially for a newbie like me who's never written a driver before.

I can do it in Python in a startup script, but that, too, seems like a heavyweight solution to a lightweight problem.

Upvotes: 0

Views: 525

Answers (1)

Andrejs Cainikovs
Andrejs Cainikovs

Reputation: 28474

That's a wrong approach. Board file supposed to register device drivers and pass important information to them, rather than act as a device driver itself. I'm not sure if what you're trying to do is even possible.

If you really need to extract something from your I2C device on a very early stage - do that in the bootloader and pass the data to kernel via cmdline (U-boot, by the way, has I2C support for a quite some time). Then later, kernel might do appropriate actions depending on what you have passed to it.

Upvotes: 1

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