[PATCH RFC v5 0/2] clk: Support for DT assigned clock parents and rates

Sylwester Nawrocki
2014-04-09T11:26:51Z

This patch set adds a DT binding documentation for new 'clock-parents'
and 'clock-rates' DT properties and a helper to parse DT and set the
specified clocks configuration. The helper is now called in the platform
bus before driver probing.

Changes since v4:
- added note explaining how to skip setting parent and rate of a clock,
- added missing call to of_node_put(),
- moved of_clk_dev_init() calls to the platform bus,
- dropped debug traces.

Thanks for the reviews.

Currently clock parent/rate setting is only handled automatically for
devices on Linux platform bus; I didn't add it to other busses this
time as the original problem this patch series is trying to solve is
related to the platform devices. However, in general it might make
sense to also add it to other busses, like: amba, I2C, SPI, etc.

The other issue is that in case of deferred probe of_clk_dev_init()
could be called multiple times. To avoid this a field could be added
to struct device or struct platform_device, etc. so a device can be
marked as initialized WRT clocks and initialization could be skipped
before any subsequent deferred probe calls.
I wasn't sure if I should bother generic device data structures with
something like this so I just didn't add it now.

Changes since v3:
- improved documentation of the DT binding,
- fixed build errors for !CONFIG_OF, the parsing helpers are only
compiled in if CONFIG_OF is set.

Changes since v2:
- code reordering to ensure there is no build errors, the clock
configuration code moved to a separate file,
- introduced an 'assigned-clocks' DT node which is supposed to contain
clocks, clock-parents, clock-rates properties and be child node
a clock provider node, and a code parsing it called from of_clk_init();
It's for clocks which are not directly connected to consumer devices.
An alternative would be to list such assigned clocks in 'clocks'
property, along with "proper" parent clocks, but then there would
be phandles in clocks property of a node pointing to itself and it
would require proper handling in of_clock_init().
I actually tried it but it looked a bit ugly and chose this time to
use an extra subnode.

Changes since v1:
- updated DT binding documentation,
- dropped the platform bus notifier, the clock setup routine is now
being called directly from the driver core before a driver probe() call;
this has an advantage such as all bus types are handled and any errors
are propagated, so that, for instance a driver probe() can be deferred
also when resources specified by clock-parents/clock-rates properties
are not yet available; an alternative would be to let drivers call
of_clk_device_setup() directly,
- dropped the patch adding a macro definition for maximum DT property
name length for now.

Open issues:
- handling of errors from of_clk_get_by_property() could be improved,
currently ENOENT is returned by this function not only for a null
entry.

This series has been tested on ARM, on Exynos4412 Trats2 board.

Sylwester Nawrocki (2):
clk: Add function parsing arbitrary clock list DT property
clk: Add handling of clk parent and rate assigned from DT

.../devicetree/bindings/clock/clock-bindings.txt | 44 ++++++++++
drivers/base/platform.c | 5 ++
drivers/clk/Makefile | 3 +
drivers/clk/clk-conf.c | 85 ++++++++++++++++++++
drivers/clk/clk.c | 12 ++-
drivers/clk/clkdev.c | 25 +++++-
include/linux/clk.h | 7 ++
include/linux/clk/clk-conf.h | 19 +++++
8 files changed, 195 insertions(+), 5 deletions(-)
create mode 100644 drivers/clk/clk-conf.c
create mode 100644 include/linux/clk/clk-conf.h

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1.7.9.5