linux-kernel - Re: [RFC PATCH 1/2] driver core: introduce module_platform_driver_match_and

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Date:	Thu, 21 Nov 2013 16:33:13 -0600
From:	Rob Herring <robherring2@...il.com>
To:	Grant Likely <grant.likely@...aro.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Rob Herring <rob.herring@...xeda.com>
Subject: Re: [RFC PATCH 1/2] driver core: introduce module_platform_driver_match_and_probe

On Thu, Nov 21, 2013 at 6:47 AM, Grant Likely <grant.likely@...aro.org> wrote:
> On Wed, 30 Oct 2013 01:12:50 -0500, Rob Herring <robherring2@...il.com> wrote:
>> From: Rob Herring <rob.herring@...xeda.com>
>>
>> Introduce a helper to match, create and probe a platform device. This
>> is for drivers such as cpuidle or cpufreq that typically don't have a
>> bus device node and need to match on a system-level compatible property.
>>
>> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>> Cc: Grant Likely <grant.likely@...aro.org>
>> Signed-off-by: Rob Herring <rob.herring@...xeda.com>
>
> Oh, ick. Please no. If a platform_device isn't getting created for a
> device tree node, then we should be asking why it isn't getting created
> and fix the core logic rather than trying to bodge it in the driver init
> code.
>
> We should never be creating and registering devices in module init code.
> We've spent the last 4 years trying to get away from that.

This is for devices that have no DT device node to be associated with
and therefore will never have a device created by the core DT code.
Instead the devices are created based off of the root compatible
property. cpuidle drivers are one such example [1]. We already do this
today by putting the platform device creation in the
machine_desc.init_machine function which is a conditional initcall.
The motivation for changing this is how to support drivers like this
on arm64 which doesn't want any platform code or machine_desc. At
least historically, we didn't want DT nodes of Linux specific devices
in the DT. So, how would you propose to solve this problem?

Rob

[1] https://git.kernel.org/cgit/linux/kernel/git/robh/linux.git/commit/?h=highbank-rm-mach-desc&id=f4c00839748688c480c56952cfc06d49aebe1162
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