linux-kernel - [PATCH v2 0/3] clk: implement remuxing during set

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Date:	Fri, 19 Apr 2013 17:28:21 +0100
From:	James Hogan <james.hogan@...tec.com>
To:	Mike Turquette <mturquette@...aro.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>
CC:	Stephen Boyd <sboyd@...eaurora.org>,
	James Hogan <james.hogan@...tec.com>
Subject: [PATCH v2 0/3] clk: implement remuxing during set_rate

This patchset adds support for automatic selection of the best parent
for a clock mux, i.e. the one which can provide the closest clock rate
to that requested. It can be controlled by a new CLK_SET_RATE_REMUX flag
so that it doesn't happen unless explicitly allowed.

This works by way of adding a new op, determine_rate, similar to
round_rate but with an extra parameter to allow the clock driver to
optionally select a different parent clock. This is used in
clk_calc_new_rates to decide whether to initiate a set_parent operation.

Changes in v2:

I've moved the mux determine_rate implementation into a core helper, but
I haven't pushed it fully into the core, as I think it just wouldn't
work correctly for more complex clocks, e.g. if you (theoretically) had
a combined mux and divide, you'd want to intercept the determine_rate
and ask for a larger rate from the parent clocks, then return the
divided rate. This should be possible by wrapping the mux determine_rate
helper.

Patch 1 still exports the __clk_get_parent_by_index as it seems like it
might be a useful thing for clock implementations to have access to if
they ever wanted to do something more fancy with changing clock parents.

I haven't made any attempt to implement the atomic set_parent+set_rate
as I don't have hardware that could take proper advantage of it, but it
shouldn't be too difficult for others to implement if they wanted since
they're fairly close to one another (in clk_change_rate()).

* switched to using new determine_rate op rather than adding an argument
  to round_rate.
* moved mux implementation into a single helper which should be usable
  from more complex clocks which can mux.
* rewrite main implementation so that no changes are made until after
  the PRE notifications have been sent, and in a way that should ensure
  correct notifications without duplicates, and I think should be safe
  in the event of a notification failing.
* various tidy ups and fixes.

James Hogan (3):
  clk: abstract parent cache
  clk: add support for clock reparent on set_rate
  clk: clk-mux: implement remuxing on set_rate

 Documentation/clk.txt        |   4 +
 drivers/clk/clk-mux.c        |   1 +
 drivers/clk/clk.c            | 216 +++++++++++++++++++++++++++++++++----------
 include/linux/clk-private.h  |   2 +
 include/linux/clk-provider.h |  12 +++
 5 files changed, 185 insertions(+), 50 deletions(-)

-- 
1.8.1.2

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