linux-kernel - Re: [PATCH] of: base: upgrade initcall level of of

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Date:	Wed, 13 May 2015 11:03:50 +0100
From:	Sudeep Holla <sudeep.holla@....com>
To:	Rob Herring <robherring2@...il.com>
CC:	Sudeep Holla <sudeep.holla@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] of: base: upgrade initcall level of of_init from core
 to pure



On 12/05/15 23:55, Rob Herring wrote:
> On Tue, May 12, 2015 at 12:38 PM, Sudeep Holla <sudeep.holla@....com> wrote:
>> Commit 5590f3196b29 ("drivers/core/of: Add symlink to device-tree from
>> devices with an OF node") adds the symlink `of_node` for each device
>> pointing to it's device tree node while creating/initialising it.
>>
>> However the devicetree sysfs is created and setup in of_init which is
>> executed at core_initcall level. For all the devices created at the core
>> initcall before of_init, the following error is thrown:
>>          "Error -2(-ENOENT) creating of_node link"
>
> What devices have you seen the problem with? I'd rather see if those
> devices could now be moved later.
>

Yes that's exactly what I attempted first after seeing the issue, but
failed miserably due to the dependency mentioned below.

It's on vexpress platforms with the following initcall sequence:
1. core - vexpress system control registers block(sysreg)
2. postcore - vexpress configuration controllers(config-bridge)
3. arch - customize_machine->of_platform_populate

of_platform_populate creates amba_devices which need clocks and
depend on the vexpress-config and clocks which in turn depends on
vexpress-sysreg

I would like to know if with commit 5590f3196b29 are we mandating
all the device creation to be done only after core_initcall or
is it OK get the errors mentioned above and ignore them as harmless
as the comment in the code states:
"An error here doesn't warrant bringing down the device"

>> Since the core_initcall is the earliest point where devices get
>> registered, push initcall level of of_init from core to pure so that
>> the devicetree sysfs is ready before any devices are registered.
>
> Read the definition of pure:
>
>   * A "pure" initcall has no dependencies on anything else, and purely
>   * initializes variables that couldn't be statically initialized.
>

Yes I read and was bit hesitant initially to do this change, but found
no better way. I posted mainly to discuss other possibilities to solve
the issue.

Regards,
Sudeep
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