linux-kernel - Re: [RFC v1 PATCH 3/3] driver: update all the code that use soc_device

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Message-ID: <YH4VdPNO9cdzc5MD@atmark-techno.com>
Date:   Tue, 20 Apr 2021 08:42:44 +0900
From:   Dominique MARTINET <dominique.martinet@...ark-techno.com>
To:     Arnd Bergmann <arnd@...db.de>
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Subject: Re: [RFC v1 PATCH 3/3] driver: update all the code that use
 soc_device_match

Arnd Bergmann wrote on Mon, Apr 19, 2021 at 02:16:36PM +0200:
> In some cases, you can use the device_link infrastructure to deal
> with dependencies between devices. Not sure if this would help
> in your case, but have a look at device_link_add() etc in drivers/base/core.c

I'll need to actually try to convince myself but if creating the link
forces driver registration then it should be workable.

> > In this particular case the problem is that since 7d981405d0fd ("soc:
> > imx8m: change to use platform driver") the soc probe tries to use the
> > nvmem driver for ocotp fuses for imx8m devices, which isn't ready yet.
> > So soc loading gets pushed back to the end of the list because it gets
> > defered and other drivers relying on soc_device_match get confused
> > because they wrongly think a device doesn't match a quirk when it
> > actually does.
> >
> > If there is a way to ensure the nvmem driver gets loaded before the soc,
> > that would also solve the problem nicely, and avoid the need to mess
> > with all the ~50 drivers which use it.
> >
> > Is there a way to control in what order drivers get loaded? Something in
> > the dtb perhaps?
> 
> For built-in drivers, load order depends on the initcall level and
> link order (how things are lined listed in the Makefile hierarchy).
> 
> For loadable modules, this is up to user space in the end.
> 
> Which of the drivers in this scenario are loadable modules?

All the drivers involved in my case are built-in (nvmem, soc and final
soc_device_match consumer e.g. caam_jr that crashes the kernel if soc is
not identified properly).

I frankly don't like the idea of moving nvmem/ above soc/ in
drivers/Makefile as a "solution" to this (especially as there is one
that seems to care about what soc they run on...), so I'll have a look
at links first, hopefully that will work out.


Thanks,
-- 
Dominique