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

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Date:	Wed, 03 Dec 2014 11:30:55 -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 Kevin, Arnd,
>
> I've been giving this some more thoughts...
>
> On Wed, Nov 26, 2014 at 9:11 PM, Kevin Hilman <khilman@...nel.org> wrote:
>> Geert Uytterhoeven <geert@...ux-m68k.org> writes:
>>> 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.
>
> Should I not add the interrupt to the device node, even though I do
> know the hardware block has an interrupt?
> Of course, to make use of the interrupt, you do need a hardware-specific
> driver that binds to the specific compatible name. But for now such a
> driver is overkill, as I do not need to use the interrupt.
>
> Power domains (and clocks used for power management) are different,
> as they are platform features: they may appear in any device node, even if
> the bindings for the device node don't mention them.
> Else I cannot add them to a node that's compatible with e.g. "arm,cortex-a15"
> or "arm,pl310-cache", without adding (or completely replacing them with)
> compatible names like "renesas,r8a73a4-cortex-a15" resp.
> "renesas,sh73a0-pl310-cache"?
> Hence I think they should be allowed in "simple-bus" nodes, too.
>
>>>> 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?
>
> That means writing bindings for a new bus type "simple-pm-bus"?

Well, I'm OK with adding common properties to simple-bus also, but
presuably you'll want to document those as well in a binding doc for
simple-bus.

Kevin

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