Re: [PATCH v2 0/4] gpio: fix an incorrect lockdep warning

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On 2016-09-16 19:58, Wolfram Sang wrote:
> 
>>> Looks good from my POV, but will wait for Peter to comment.
>>>
>>> If accepted, I'd think this should go via my I2C tree and I would like
>>> to ask Linus to ack patch 4. D'accord, everyone?
>>
>> Since it is not clear if "Peter" is me or PeterZ (I suspect PeterZ...),
> 
> Nope, I meant you :) I really value your input, it especially helps me
> on topics like locking, nesting, muxing... etc. Much appreciated, thanks
> a lot for doing that!
> 
>> I'm just adding that it all looks fine by me as well, just to prevent
>> this from being held up by a misunderstanding.
> 
> OK. I read this as Acked-by.
> 
>> It does unconditionally add a new function to i2c-core that is only
>> ever used if lockdep is enabled, but it is tiny and I'm not bothered
>> by that memory waste.
> 
> Same here. And if it prevents us from false positive lockdep reports, I
> am all for fixing it.

Except it doesn't, when I think some more about it...

If you have two gpio-expanders on the same depth but on different i2c
branches you still end up with a splat if one is used to control a mux
to reach the other.

The only way to solve it for good, that I see, is to have every instance
of the gpio-expander mutex in its own class. That might lead to many
lockdep classes but then again, how many gpio expanders could there be
in a system? A dozen or two seems extreme, so maybe that is the correct
approach anyway?

Cheers,
Peter

--
To unsubscribe from this list: send the line "unsubscribe linux-i2c" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html



[Index of Archives]     [Linux GPIO]     [Linux SPI]     [Linux Hardward Monitoring]     [LM Sensors]     [Linux USB Devel]     [Linux Media]     [Video for Linux]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]

  Powered by Linux