The clock accuracy is expressed in ppb (parts per billion) and represents
the possible clock drift.
Say you have a clock (e.g. an oscillator) which provides a fixed clock of
20MHz with an accuracy of +- 20Hz. This accuracy expressed in ppb is
20Hz/20MHz = 1000 ppb (or 1 ppm).
Clock users may need the clock accuracy information in order to choose
the best clock (the one with the best accuracy) across several available
clocks.
This patch adds clk accuracy retrieval support for common clk framework by
means of a new function called clk_get_accuracy.
This function returns the given clock accuracy expressed in ppb.
In order to get the clock accuracy, this implementation adds one callback
called recalc_accuracy to the clk_ops structure.
This callback is given the parent clock accuracy (if the clock is not a
root clock) and should recalculate the given clock accuracy.
This callback is optional and may be implemented if the clock is not
a perfect clock (accuracy != 0 ppb).
Signed-off-by: Boris BREZILLON <b.brezillon@overkiz.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>
Add core support to allow clock implementations to select the best
parent clock when rounding a rate, e.g. the one which can provide the
closest clock rate to that requested. This is by way of adding a new
clock op, determine_rate(), which is like round_rate() but has an extra
parameter to allow the clock implementation to optionally select a
different parent clock. The core then takes care of reparenting the
clock when setting the rate.
The parent change takes place with the help of some new private data
members. struct clk::new_parent specifies a clock's new parent (NULL
indicates no change), and struct clk::new_child specifies a clock's new
child (whose new_parent member points back to it). The purpose of these
are to allow correct walking of the future tree for notifications prior
to actually reparenting any clocks, specifically to skip child clocks
who are being reparented to another clock (they will be notified via the
new parent), and to include any new child clock. These pointers are set
by clk_calc_subtree(), and the new_child pointer gets cleared when a
child is actually reparented to avoid duplicate POST_RATE_CHANGE
notifications.
Each place where round_rate() is called, determine_rate() is checked
first and called in preference. This restructures a few of the call
sites to simplify the logic into if/else blocks.
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>
Cc: Mike Turquette <mturquette@linaro.org>
Cc: linux-arm-kernel@lists.infradead.org
Signed-off-by: Mike Turquette <mturquette@linaro.org>
This is primarily useful when there's a driver that doesn't claim clocks
properly, but the bootloader leaves them on. It's not expected to be used
in normal cases, but for bringup and debug it's very useful to have the
option to not gate unclaimed clocks that are still on.
Signed-off-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Mike Turquette <mturquette@linaro.org>
[mturquette@linaro.org: fixed up trivial merge issue]
Provide documentation for the common clk structures and APIs. This code
can be found in drivers/clk/ and include/linux/clk*.h.
Signed-off-by: Mike Turquette <mturquette@linaro.org>
Signed-off-by: Mike Turquette <mturquette@ti.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Jeremy Kerr <jeremy.kerr@canonical.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Arnd Bergman <arnd.bergmann@linaro.org>
Cc: Paul Walmsley <paul@pwsan.com>
Cc: Shawn Guo <shawn.guo@freescale.com>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Richard Zhao <richard.zhao@linaro.org>
Cc: Saravana Kannan <skannan@codeaurora.org>
Cc: Magnus Damm <magnus.damm@gmail.com>
Cc: Rob Herring <rob.herring@calxeda.com>
Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: Linus Walleij <linus.walleij@stericsson.com>
Cc: Stephen Boyd <sboyd@codeaurora.org>
Cc: Amit Kucheria <amit.kucheria@linaro.org>
Cc: Deepak Saxena <dsaxena@linaro.org>
Cc: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Boris BREZILLON
James Hogan
Sachin Kamat
Olof Johansson
Eduardo Valentin
Mike Turquette