[PATCH v3/resend 0/4] drivers: bus: Add Simple Power-Managed Bus

[Geert Uytterhoeven]

	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 just enables runtime PM for the bus device.
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.

Currently this driver supports the Renesas Bus State Controller only,
but support for other SoCs and other bus controllers can easily be
added later by adding more compatible values.
Note that this driver cannot just bind against "simple-bus", as that
may prevent a device-specific driver from taking precedence.

This was tested on sh73a0/kzm9g-multiplatform (by me), and on
r8a73a4/ape6evm-multiplatform (by Ulrich Hecht). Without this,
Ethernet doesn't work, as the ZB clock is disabled by
clk_disable_unused().

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.

Changes compared to v2:
  - Document required properties inherited from "simple-bus",
  - Document required "reg" property for "renesas,bsc",
  - Move "ranges" before "reg" in the example,
  - Add Tested-by,
  - Split-off sh73a0/kzm9g and r8a73a4/ape6evm DTS updates.

Changes compared to v1 (more detailed change logs in the individual
patches):
  - Added sorting of drivers/bus Kconfig and Makefile entries,
  - Added DT binding documentation,
  - Rename from "Renesas Bus State Controller Driver" (renesas-bsc) to
    "Simple Power-Managed Bus Driver" (simple-pm-bus),
  - Postponed adding power-domains properties to the dtsi,
  - Added updates for r8a73a4/ape6evm.

Thanks for your review comments!

Geert Uytterhoeven (4):
  drivers: bus: Sort Kconfig entries alphabetically
  drivers: bus: Sort Makefile entries alphabetically
  drivers: bus: Add Simple Power-Managed Bus DT Bindings
  drivers: bus: Add Simple Power-Managed Bus Driver

 .../devicetree/bindings/bus/simple-pm-bus.txt      | 52 +++++++++++++++++++++
 drivers/bus/Kconfig                                | 53 ++++++++++++++--------
 drivers/bus/Makefile                               | 15 +++---
 drivers/bus/simple-pm-bus.c                        | 51 +++++++++++++++++++++
 4 files changed, 144 insertions(+), 27 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/bus/simple-pm-bus.txt
 create mode 100644 drivers/bus/simple-pm-bus.c

-- 
1.9.1

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

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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