[U-Boot] [RFC] Make i2c probe opt-outable?

[Tom Rini]

On 05/17/2012 07:48 PM, Mike Frysinger wrote:
> On Thursday 17 May 2012 14:43:45 Tom Rini wrote:
>> I'd like to propose making 'i2c probe' be a command that is
>> opt-out'able.  In the Linux Kernel the notion of probing for devices was
>> abandoned a while ago due to, in short, devices misbehaving when
>> randomly poked at.  Over in omap24xx_i2c land we changed our probe
>> method a while ago from an attempted read to an attempted write as some
>> i2c devices would NAK the read.  But now with the am33xx SoM family we
>> have a new issue which is that attempting to write to an address doesn't
>> immediately issue a NAK so probe sees all addresses as valid and in turn
>> leaves the bus upset.  I've worked around this for now by making
>> i2c_probe use the read method instead, only on am33xx (so most devices
>> would be spotted, but the ones that caused the initial change would not
>> show up).  But a possibly better solution is to just make the i2c probe
>> command not implemented for am33xx (as you don't have to run i2c probe
>> to try and use your device).
>
> i've always seen the "i2c probe" command as a debugging tool, not something
> that you need to do to make things work.  so along those lines, isn't it
> already optional ?  if you don't like it, don't run it :).

Including a command that doesn't work and saying "ah, just don't use 
that" is asking for trouble.  I'm going down the "what changed in the IP 
block, really" rat-hole now (since I've got the original test working). 
  But still, the kernel decided i2c probing is dangerous/unreliable, 
maybe we should follow, or at least allow boards to follow?

-- 
Tom