Re: [PATCH] pinctrl: mediatek: convert to arch_initcall

[Matthias Brugger]

On January 1, 2016 3:56:01 AM EET, Daniel Kurtz <djkurtz@xxxxxxxxxxxx> wrote:
>Hi Mark,
>
>Thanks for responding.
>
>On Fri, Jan 1, 2016 at 6:07 AM, Mark Brown <broonie@xxxxxxxxxx> wrote:
>> On Thu, Dec 31, 2015 at 09:45:51PM +0800, Daniel Kurtz wrote:
>>> On Thu, Dec 31, 2015 at 1:22 AM, Mark Brown <broonie@xxxxxxxxxx>
>wrote:
>>
>>> > I really don't think we should be applying this sort of stuff
>unless
>>> > things are actively broken right now.  It's a bit of a rabbit hole
>we
>>> > could spend a long time going down tweaking things for different
>>> > systems in the same way that tweaking the link order can be and it
>masks
>>> > the underlying issues.
>>
>>> Things are actively broken right now, in the sense that there are
>many
>>> needless probe deferrals on boot.
>>
>> That's just noisy, everything does end up loading OK.
>
>It's not just noisy, it also adds to boot time.
>
>>  If the noise is a
>> problem working on fixing the underlying problem with not being able
>to
>> figure out dependencies seems like a better thing.  When we discussed
>> this on the kernel summit list it wasn't clear everyone was convinced
>> this was even a problem (I think it is since it obscures real
>> information).  Actual breakage to me is something that never sorts
>> itself out.
>>
>>> These are pinctrl drivers, which are required to load before every
>>> other driver that requests a gpio.
>>> AFAICT, the pinctrl is part of the platform "architecture", hence
>why
>>> I suggest we move this to arch_initcall().
>>
>> This is exactly the sort of hacking that leads to problems
>
>What problems?
>More patches as people adjust / tune / optimize boot time, or something
>else?
>
>> you can
>> also make the same argument for a bunch of other things like
>regulators
>> but then you find there's circular dependencies or extra devices with
>> different requirements on some systems that cause further issues and
>> need more special casing, or you find that some other device gets
>pushed
>> earlier so you have to go round tweaking everything it uses.
>
>For regulators, I think things are a bit more subtle.  Most regulators
>are external components that can be used on different boards for
>different purposes, so I can see an argument for treating them in a
>more generic way by using a later device_initcall.  The exception
>being architecture specific PMICs that only make sense when paired
>with a specific small set of CPUs - and if you look, there are many
>PMIC regulator drivers that are at earlier initcall levels, presumably
>because they are required by cpufreq drivers, and/or their initcall
>level is set as the same as the rest of the functions exposed by the
>same PMIC MFD.
>
>> It's not
>> that the device is magic, it's that we don't understand how to handle
>> dependencies well enough.  Raphael did say he was going to work on
>> something for this, I'm not sure where it got to though.
>
>Glad to hear it is a well recognized problem, and that people plan to
>look into a fix.
>
>>> arch_initcall() is also consistent with 39 other pinctrl drivers in
>>> drivers/pinctrl.
>>> 19 others use subsys_initcall(), core_initcall() or
>>> postcore_initcall(), any of which would also work.
>>
>> It's fairly clear that there's at least a case for simplifying the
>> existing practice here, for example by moving everything into a
>single
>> (perhaps aliased) initcall rather than by randomly picking a level
>per
>> system or by actually fiddling with the link ordering if the case is
>> sufficiently clear that pinctrl in general ought to load earlier than
>it
>> does.
>
>Nothing above sounds like a reason not to merge this patch, however.
>Why should we block useful patches that use existing tools to fix real
>architecture-specific issues until new infrastructure is merged that
>solves general problems?
>

I think what Mark means is, that we define some pinctrl_initcall which is a macro to subsys_initcall (or arch_initcall or similar). We apply this to all pinctrl drivers including the one from Mediatek. This way at least we have a common method and changing the behaviour in the future is easier to handle.

Regards,
Matthias

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