Re: [PATCH] i2c: Let users disable "Probe an I2C bus for certaindevices"

From: Grygorii Strashko
Date: Fri Jun 07 2013 - 06:14:20 EST

Hi Wolfram,
On 06/07/2013 12:06 PM, Wolfram Sang wrote:
3) Thinking about Mainline: To reach the same target - no I2C
detection - and taking
into account above assumption "No changes in default behavior"
the following will need to be done:
- change i2c-omap/i2c-gpio DT bindings and add parameter which will
allow to change
.class value for adapter. Not sure, it's possible because this parameter
will be Linux and not HW specific (smth. like "i2c_disable_detection")
- update drivers i2c-omap/i2c-gpio to use "i2c_disable_detection"
- update OMAP4/5 DTS files

So, It seemed a good solution for me to add 6 lines of code in i2c-core.c
instead of doing all that stuff.
Well... I understand the "default behaviour" issue, yet I still think
that setting class to 0 is the right thing to do. OMAP is an embedded
SoC which always had i2c_board_info or devictree which are the preferred
ways of instantiating. Given that, I would accept a patch setting it to
0. The more user friendly way might be to introduce a new class which
makes users aware of the issue. Proof of concept follows, only compile

That sounds good to me - I can prepare patch for i2c-omap.c.
But, there is still an open question regarding *i2c-gpio.c* which,
actually, a source of biggest part of delay.

Potentially, it can be tunned using "timeout" value. But, again, this
is additional work/patches to workaround unneeded system feature:
- "timeout" should not break interaction with I2C devices on i2c-gpio
bus and, at same time, speed up boot;
- DTS/board files need to be updated.

May be, just may be), we can continue with CONFIG_I2C_DISABLE_DEVICE_DETECTION,
and print deprecation warning for each registered adapter
if this config option is defined.

- grygorii
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at