summaryrefslogtreecommitdiffstats
path: root/Documentation/clk.txt
diff options
context:
space:
mode:
authorJames Hogan <james.hogan@imgtec.com>2013-07-29 12:25:00 +0100
committerMike Turquette <mturquette@linaro.org>2013-08-19 12:27:17 -0700
commit71472c0c06cf9a3d1540762ea205654c584e3bc4 (patch)
tree22db34b3c7bc0d0053fcfac2c95d77adf09107de /Documentation/clk.txt
parent4935b22c46ea5e2dc44ef0b72db50741649eb3a4 (diff)
downloadop-kernel-dev-71472c0c06cf9a3d1540762ea205654c584e3bc4.zip
op-kernel-dev-71472c0c06cf9a3d1540762ea205654c584e3bc4.tar.gz
clk: add support for clock reparent on set_rate
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>
Diffstat (limited to 'Documentation/clk.txt')
-rw-r--r--Documentation/clk.txt46
1 files changed, 26 insertions, 20 deletions
diff --git a/Documentation/clk.txt b/Documentation/clk.txt
index 6f68ba0..3aeb5c4 100644
--- a/Documentation/clk.txt
+++ b/Documentation/clk.txt
@@ -70,6 +70,10 @@ the operations defined in clk.h:
unsigned long parent_rate);
long (*round_rate)(struct clk_hw *hw, unsigned long,
unsigned long *);
+ long (*determine_rate)(struct clk_hw *hw,
+ unsigned long rate,
+ unsigned long *best_parent_rate,
+ struct clk **best_parent_clk);
int (*set_parent)(struct clk_hw *hw, u8 index);
u8 (*get_parent)(struct clk_hw *hw);
int (*set_rate)(struct clk_hw *hw, unsigned long);
@@ -179,26 +183,28 @@ mandatory, a cell marked as "n" implies that either including that
callback is invalid or otherwise unnecessary. Empty cells are either
optional or must be evaluated on a case-by-case basis.
- clock hardware characteristics
- -----------------------------------------------------------
- | gate | change rate | single parent | multiplexer | root |
- |------|-------------|---------------|-------------|------|
-.prepare | | | | | |
-.unprepare | | | | | |
- | | | | | |
-.enable | y | | | | |
-.disable | y | | | | |
-.is_enabled | y | | | | |
- | | | | | |
-.recalc_rate | | y | | | |
-.round_rate | | y | | | |
-.set_rate | | y | | | |
- | | | | | |
-.set_parent | | | n | y | n |
-.get_parent | | | n | y | n |
- | | | | | |
-.init | | | | | |
- -----------------------------------------------------------
+ clock hardware characteristics
+ -----------------------------------------------------------
+ | gate | change rate | single parent | multiplexer | root |
+ |------|-------------|---------------|-------------|------|
+.prepare | | | | | |
+.unprepare | | | | | |
+ | | | | | |
+.enable | y | | | | |
+.disable | y | | | | |
+.is_enabled | y | | | | |
+ | | | | | |
+.recalc_rate | | y | | | |
+.round_rate | | y [1] | | | |
+.determine_rate | | y [1] | | | |
+.set_rate | | y | | | |
+ | | | | | |
+.set_parent | | | n | y | n |
+.get_parent | | | n | y | n |
+ | | | | | |
+.init | | | | | |
+ -----------------------------------------------------------
+[1] either one of round_rate or determine_rate is required.
Finally, register your clock at run-time with a hardware-specific
registration function. This function simply populates struct clk_foo's
OpenPOWER on IntegriCloud