[RFC PATCH 2/3] clk: adjust clocks to their requested rate after parent changes

Heiko Stuebner
2016-05-02T16:36:21Z

Given a hirarchy of clk1 -> [div] -> clk2, when the rate of clk1 gets
changed, clk2 changes as well as the divider stays the same. There may
be cases where a user of clk2 needs it at a specific rate, so clk2
needs to be readjusted for the changed rate of clk1.

So if a rate was requested for the clock, and its rate changed during
the underlying rate-change, with this change the clock framework now
tries to readjust the rate back to/near the requested one.

The whole process is protected by a new clock-flag to not force this
behaviour change onto every clock defined in the ccf.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
---
drivers/clk/clk.c | 13 +++++++++++--
include/linux/clk-provider.h | 1 +
2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index 65e0aad..22be369 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -1410,6 +1410,9 @@ static struct clk_core *clk_propagate_rate_change(struct clk_core *core,
return fail_clk;
}

+static int clk_core_set_rate_nolock(struct clk_core *core,
+ unsigned long req_rate);
+
/*
* walk down a subtree and set the new rates notifying the rate
* change on the way
@@ -1494,6 +1497,12 @@ static void clk_change_rate(struct clk_core *core)
/* handle the new child who might not be in core->children yet */
if (core->new_child)
clk_change_rate(core->new_child);
+
+ /* handle a changed clock that needs to readjust its rate */
+ if (core->flags & CLK_KEEP_REQ_RATE && core->req_rate
+ && core->new_rate != old_rate
+ && core->new_rate != core->req_rate)
+ clk_core_set_rate_nolock(core, core->req_rate);
}

static int clk_core_set_rate_nolock(struct clk_core *core,
@@ -1529,11 +1538,11 @@ static int clk_core_set_rate_nolock(struct clk_core *core,
return -EBUSY;
}

+ core->req_rate = req_rate;
+
/* change the rates */
clk_change_rate(top);

- core->req_rate = req_rate;
-
return ret;
}

diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
index 0c72204..06f189e 100644
--- a/include/linux/clk-provider.h
+++ b/include/linux/clk-provider.h
@@ -33,6 +33,7 @@
#define CLK_RECALC_NEW_RATES BIT(9) /* recalc rates after notifications */
#define CLK_SET_RATE_UNGATE BIT(10) /* clock needs to run to set rate */
#define CLK_IS_CRITICAL BIT(11) /* do not gate, ever */
+#define CLK_KEEP_REQ_RATE BIT(12) /* keep reqrate on parent rate change */

struct clk;
struct clk_hw;
--
2.8.0.rc3