From: Thierry Reding <[email protected]> This new function is similar to clk_set_parent(), except that it doesn't actually change the parent. It merely checks that the given parent clock can be a parent for the given clock.
A situation where this is useful is to check that a particular setup is valid before switching to it. One specific use-case for this is atomic modesetting in the DRM framework where setting a mode is divided into a check phase where a given configuration is validated before applying changes to the hardware. Signed-off-by: Thierry Reding <[email protected]> --- drivers/clk/clk.c | 36 ++++++++++++++++++++++++++++++++++++ include/linux/clk.h | 9 +++++++++ 2 files changed, 45 insertions(+) diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c index 01e5009c3e86..7e1c819aa6fc 100644 --- a/drivers/clk/clk.c +++ b/drivers/clk/clk.c @@ -1673,6 +1673,42 @@ void __clk_reparent(struct clk *clk, struct clk *new_parent) } /** + * clk_try_parent - check if a clock can be the parent clock source of another + * @clk: clock source + * @parent: parent clock source + * + * This is like clk_set_parent(), except that it only checks that parent can + * be the parent clock source for clock. + * + * Returns success (0) or negative errno. + */ +int clk_try_parent(struct clk *clk, struct clk *parent) +{ + int err = 0; + + if (!clk || !parent) + return -EINVAL; + + if ((clk->num_parents > 1) && !clk->ops->set_parent) + return -ENOSYS; + + clk_prepare_lock(); + + if (clk->parent == parent) + goto unlock; + + err = clk_fetch_parent_index(clk, parent); + if (err > 0) + err = 0; + +unlock: + clk_prepare_unlock(); + + return err; +} +EXPORT_SYMBOL_GPL(clk_try_parent); + +/** * clk_set_parent - switch the parent of a mux clk * @clk: the mux clk whose input we are switching * @parent: the new input to clk diff --git a/include/linux/clk.h b/include/linux/clk.h index fb1ac65f127c..d8e9b8865d38 100644 --- a/include/linux/clk.h +++ b/include/linux/clk.h @@ -328,6 +328,15 @@ long clk_round_rate(struct clk *clk, unsigned long rate); int clk_set_rate(struct clk *clk, unsigned long rate); /** + * clk_try_parent - check if a clock can be the parent clock source of another + * @clk: clock source + * @parent: parent clock source + * + * Returns success (0) or negative errno. + */ +int clk_try_parent(struct clk *clk, struct clk *parent); + +/** * clk_set_parent - set the parent clock source for this clock * @clk: clock source * @parent: parent clock source -- 2.1.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
