linux-kernel - Re: [PATCH RFC 0/3] Add "Simple" / Renesas Bus State Controller Driver

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Date:	Wed, 26 Nov 2014 12:11:12 -0800
From:	Kevin Hilman <khilman@...nel.org>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	Arnd Bergmann <arnd@...db.de>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Ulrich Hecht <ulrich.hecht+renesas@...il.com>,
	Simon Horman <horms@...ge.net.au>,
	Magnus Damm <magnus.damm@...il.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Grant Likely <grant.likely@...aro.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	"devicetree\@vger.kernel.org" <devicetree@...r.kernel.org>,
	Linux-sh list <linux-sh@...r.kernel.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC 0/3] Add "Simple" / Renesas Bus State Controller Driver

Geert Uytterhoeven <geert@...ux-m68k.org> writes:

> Hi Arnd,
>
> On Mon, Nov 24, 2014 at 9:15 PM, Arnd Bergmann <arnd@...db.de> wrote:
>> On Monday 24 November 2014 21:10:05 Geert Uytterhoeven wrote:
>>> As this minimal BSC driver isn't hardware-specific at all, I'm wondering
>>> if there's a simpler way to do this?
>>>   - Should the driver be renamed to "simple-bus", and match "simple-bus"?
>>>   - Should this be moved to core code, without an explicit driver for
>>>     "simple-bus"? I.e. should the driver core just enable runtime PM for
>>>     all devices not bound to a driver, as they may represent buses with
>>>     child devices that do rely on runtime PM?
>>>
>>> Thanks for your comments and suggestions!
>>
>> My understanding of simple-bus is that it's something that does
>> not have any power-management capabilities, and I'd rather not
>> add clocks or interrupts to it.
>
> OK.
>
>> What I think makes more sense is to have a bus driver for it
>> in drivers/bus, remove the "simple-bus" compatibility value
>> and have the driver take care of registering the power domain
>> and probing the child devices using of_platform_populate on
>> itself.
>
> Registering power domains is already handled by the core code.
>
> So compared to my RFC code, I only have to
>   1. Drop "simple-bus" from the compatible property in the .dtsi,
>   2. Call of_platform_populate() from renesas_bsc_probe(), to
>      register the child devices, now the core code no longer does that.
>
> I find it a bit strange having to add _more_ code, as the core code handles
> registering child devices fine. Doing it from my bus driver only protects
> against people trying to run a kernel without my bus driver included
> (which currently works fine, as long as no PM domain or clock is involved,
>  e.g. if the clock is forgotten in the SoC's .dtsi :-).

I actually rather like the simple bus driver in it's current form, where
the device and pm-domain registration is taken care of by the
core. Since it's really not HW specific at all, maybe just rename it
simple-pm-bus or something like that?

Kevin

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