linux-kernel - Re: [PATCH v5 0/5] drivers: bus: Add Simple Power-Managed Bus

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Date:	Sun, 15 Feb 2015 10:45:57 -0500
From:	Simon Horman <horms@...ge.net.au>
To:	Geert Uytterhoeven <geert+renesas@...der.be>
Cc:	Rob Herring <robh+dt@...nel.org>, Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Grant Likely <grant.likely@...aro.org>,
	Arnd Bergmann <arnd@...db.de>,
	Kevin Hilman <khilman@...nel.org>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Felipe Balbi <balbi@...com>, Olof Johansson <olof@...om.net>,
	Magnus Damm <magnus.damm@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	devicetree@...r.kernel.org, linux-sh@...r.kernel.org,
	linux-pm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 0/5] drivers: bus: Add Simple Power-Managed Bus

On Wed, Feb 11, 2015 at 09:18:35AM +0900, Simon Horman wrote:
> Hi Geert,
> 
> On Thu, Feb 05, 2015 at 11:11:23AM +0100, Geert Uytterhoeven wrote:
> >         Hi all,
> > 
> > The Renesas Bus State Controller (BSC) provides an external bus for
> > connecting multiple external devices to an SoC, driving several chip
> > select lines, for e.g. NOR FLASH, Ethernet and USB.
> > On the kzm9g and ape6evm development boards, an smsc9220 Ethernet
> > controller is connnected to the BSC of an SH-Mobile AG5 (sh73a0) resp.
> > R-Mobile APE6 (r8a73a4) SoC.
> > 
> > The BSC is a fairly simple memory-mapped bus, hence a "simple-bus"
> > compatibility seems suitable.  However, the BSC is special in two
> > ways:
> >   1. It is part of a PM domain (A4S on sh73a0),
> >   2. It has a gateable functional clock (ZB).
> > Before a device connected to the BSC can be accessed, the PM domain
> > containing the BSC must be powered on, and the functional clock
> > driving the BSC must be enabled.
> > 
> > Both special properties can be described in DT in a standardized way
> > ("power-domains = <&pd_a4s>" and "clocks = <&zb_clk>", cfr. the
> > example in the DT binding documentation).  Externally connected
> > devices are described as children of the BSC node.
> > 
> > Unfortunately this doesn't mean everything will work out-of-the-box.
> > There are two problems:
> >   1. Without a device driver bound to the bus device, this device is
> >      not attached to the PM domain. And although a child device is
> >      present and active, the PM domain may be powered down, as it's
> >      considered unused by the PM domain core.
> >   2. Without a device driver calling pm_runtime_enable(), its
> >      functional clock is not enabled. Once runtime PM is enabled, the
> >      R-Mobile PM domain platform driver manages the functional clock
> >      using runtime PM.
> > 
> > As none of the above is really bus hardware-specific (PM domains and
> > functional clocks in clock domains are handled from genpd and platform
> > code), this series adds a Simple Power-Managed Bus driver for
> > transparent busses, which matches against "simple-pm-bus", enables
> > runtime PM for the bus device, and calls of_platform_populate() to
> > probe for child devices.
> > Due to the child-parent relationship of devices connected to the bus,
> > as long as the device drivers for the child devices are runtime PM
> > enabled, the bus's PM domain will be powered, and the bus's clock will
> > be enabled automatically when needed, for both runtime PM and s2ram.
> > 
> > This was tested on sh73a0/kzm9g-multiplatform (by me), and (v3) on
> > r8a73a4/ape6evm-multiplatform (by Ulrich Hecht). Without this,
> > Ethernet doesn't work, as the ZB clock is disabled by
> > clk_disable_unused().
> > 
> > Felipe: It looks like drivers/usb/musb/musb_am335x.c can be removed, if
> > "ti,am33xx-usb" claims compatibility with "simple-pm-bus"?
> > 
> > As drivers/bus doesn't have a maintainer, and this driver is needed to
> > move two shmobile platforms away from legacy to multiplatform, I think
> > this can go in through Simon's shmobile tree.
> 
> thanks for persisting with this. From my point of view it appears
> to be reviewed and ready.
> 
> Does anyone object to me queueing this up for v3.21 in the renesas tree?
> 
> Acked-by: Simon Horman <horms+renesas@...ge.net.au>

As no one has objected and it seems has been thoroughly reviewed
I have queued this up in the renesas tree.

It is part of the renesas-devel-20150215-v3.19 tag.

[snip]
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