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

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Date:	Mon, 24 Nov 2014 21:27:06 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	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@...r.kernel.org" <devicetree@...r.kernel.org>,
	Linux-sh list <linux-sh@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC 0/3] Add "Simple" / Renesas Bus State Controller Driver

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 :-).

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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