Re: [PATCH 00/21] On-demand device registration

Alexander Holler
2015-06-11T11:49:22Z

Am 11.06.2015 um 13:24 schrieb Alexander Holler:
> Am 11.06.2015 um 12:17 schrieb Alexander Holler:
>> Am 11.06.2015 um 10:12 schrieb Linus Walleij:
>>> On Wed, Jun 10, 2015 at 10:28 AM, Alexander Holler
>>> <holler-SXC+2es9fhnfWeYVQQPykw@public.gmane.org> wrote:
>>>> Am 10.06.2015 um 09:30 schrieb Linus Walleij:
>>>
>>>>> i2c host comes out, probes the regulator driver, regulator driver
>>>>> probes and then the regulator_get() call returns.
>>>>>
>>>>> This requires instrumentation on anything providing a resource
>>>>> to another driver like those I mentioned and a lot of overhead
>>>>> infrastructure, but I think it's the right approach. However I don't
>>>>> know if I would ever be able to pull that off myself, I know talk
>>>>> is cheap and I should show the code instead.
>>>>
>>>> You would end up with the same problem of deadlocks as currently, and
>>>> you
>>>> would still need something ugly like the defered probe brutforce to
>>>> avoid
>>>> them.
>>>
>>> Sorry I don't get that. Care to elaborate on why?
>>
>> Because loading/initializing on demand doesn't give you any solved order
>> of drivers to initialize. And it can't because it has no idea about the
>> requirements of other drivers. The reason why it might work better in
>> the case of the tegra is that it might give you another initialization
>> order than the one which is currently choosen, which, by luck, might be
>> a better one.
>>
>> But maybe I missed something, I haven't looked at the patches at all.
>> But just loading on demand, can't magically give you a working order of
>> drivers to initialize. E.g. how do you choose the first driver to
>> initialize?
>
> Other problems you will run into are time constraints and multithreaded
> drivers.
>
> E.g. we all should know how tricky it sometimes is to avoid deadlocks.
> And with loading on demand, you are extending this problem over the
> initialization of maybe a whole bunch of other drivers which might be
> started by calling one function of another driver. And a function call
> might need a very long time to finish during which an unpredictable
> amount of things may happen.
>
> It would make me wonder if that will end up with a good, usable and as
> simple as possible solution.

Besides that instrumenting every call to another driver in order to fix
a onetime operation (the initialization) sounds like an enormous
overhead. Initialization is done pnly once, regardless how long a system
runs, but the instrumentation to fix this onetime operation would slow
down the operation during the whole runtime of a system.

I don't think this is what should be done.

>
> Regards,
>
> Alexander Holler