[v3,34/65] clk: ux500: prcmu: Add a determine_rate hook

Commit Message

Maxime Ripard April 4, 2023, 10:11 a.m. UTC

The UX500 PRCMU "clkout" clock implements a mux with a set_parent hook,
but doesn't provide a determine_rate implementation.

This is a bit odd, since set_parent() is there to, as its name implies,
change the parent of a clock. However, the most likely candidate to
trigger that parent change is a call to clk_set_rate(), with
determine_rate() figuring out which parent is the best suited for a
given rate.

The other trigger would be a call to clk_set_parent(), but it's far less
used, and it doesn't look like there's any obvious user for that clock.

So, the set_parent hook is effectively unused, possibly because of an
oversight. However, it could also be an explicit decision by the
original author to avoid any reparenting but through an explicit call to
clk_set_parent().

The latter case would be equivalent to setting the flag
CLK_SET_RATE_NO_REPARENT, together with setting our determine_rate hook
to __clk_mux_determine_rate(). Indeed, if no determine_rate
implementation is provided, clk_round_rate() (through
clk_core_round_rate_nolock()) will call itself on the parent if
CLK_SET_RATE_PARENT is set, and will not change the clock rate
otherwise. __clk_mux_determine_rate() has the exact same behavior when
CLK_SET_RATE_NO_REPARENT is set.

And if it was an oversight, then we are at least explicit about our
behavior now and it can be further refined down the line.

Acked-by: Linus Walleij <[e-mail]>
Signed-off-by: Maxime Ripard <[e-mail]>
---
 drivers/clk/ux500/clk-prcmu.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Comments

Linus Walleij April 4, 2023, 1:44 p.m. UTC | #1

On Tue, Apr 4, 2023 at 2:45 PM Maxime Ripard <[e-mail]> wrote:

> The UX500 PRCMU "clkout" clock implements a mux with a set_parent hook,
> but doesn't provide a determine_rate implementation.
>
> This is a bit odd, since set_parent() is there to, as its name implies,
> change the parent of a clock. However, the most likely candidate to
> trigger that parent change is a call to clk_set_rate(), with
> determine_rate() figuring out which parent is the best suited for a
> given rate.

Not even that.

The parent is selected from the second cell of the device tree
specifier, and the divisor from the third cell. See:
Documentation/devicetree/bindings/clock/stericsson,u8500-clks.yaml

So this definitely does not reparent.

Yours,
Linus Walleij

Patch

diff --git a/drivers/clk/ux500/clk-prcmu.c b/drivers/clk/ux500/clk-prcmu.c
index 4deb37f19a7c..7118991f3731 100644
--- a/drivers/clk/ux500/clk-prcmu.c
+++ b/drivers/clk/ux500/clk-prcmu.c
@@ -344,6 +344,7 @@  static const struct clk_ops clk_prcmu_clkout_ops = {
 	.prepare = clk_prcmu_clkout_prepare,
 	.unprepare = clk_prcmu_clkout_unprepare,
 	.recalc_rate = clk_prcmu_clkout_recalc_rate,
+	.determine_rate = __clk_mux_determine_rate,
 	.get_parent = clk_prcmu_clkout_get_parent,
 	.set_parent = clk_prcmu_clkout_set_parent,
 };
@@ -383,7 +384,7 @@  struct clk_hw *clk_reg_prcmu_clkout(const char *name,
 
 	clk_prcmu_clkout_init.name = name;
 	clk_prcmu_clkout_init.ops = &clk_prcmu_clkout_ops;
-	clk_prcmu_clkout_init.flags = CLK_GET_RATE_NOCACHE;
+	clk_prcmu_clkout_init.flags = CLK_GET_RATE_NOCACHE | CLK_SET_RATE_NO_REPARENT;
 	clk_prcmu_clkout_init.parent_names = parent_names;
 	clk_prcmu_clkout_init.num_parents = num_parents;
 	clk->hw.init = &clk_prcmu_clkout_init;