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

[Heiko Stuebner]

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 at 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