[v3,14/65] clk: lochnagar: Add a determine_rate hook

Commit Message

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

The lochnagar clocks implement 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.

Signed-off-by: Maxime Ripard <[e-mail]>
---
 drivers/clk/clk-lochnagar.c | 2 ++
 1 file changed, 2 insertions(+)

Comments

Charles Keepax May 4, 2023, 1:39 p.m. UTC | #1

On Tue, Apr 04, 2023 at 12:11:04PM +0200, Maxime Ripard wrote:
> The lochnagar clocks implement 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.
> 
> Signed-off-by: Maxime Ripard <[e-mail]>
> ---

Tested-by: Charles Keepax <[e-mail]>

Thanks,
Charles

Patch

diff --git a/drivers/clk/clk-lochnagar.c b/drivers/clk/clk-lochnagar.c
index 80944bf482e9..820c05732ac7 100644
--- a/drivers/clk/clk-lochnagar.c
+++ b/drivers/clk/clk-lochnagar.c
@@ -209,6 +209,7 @@  static u8 lochnagar_clk_get_parent(struct clk_hw *hw)
 static const struct clk_ops lochnagar_clk_ops = {
 	.prepare = lochnagar_clk_prepare,
 	.unprepare = lochnagar_clk_unprepare,
+	.determine_rate = __clk_mux_determine_rate,
 	.set_parent = lochnagar_clk_set_parent,
 	.get_parent = lochnagar_clk_get_parent,
 };
@@ -238,6 +239,7 @@  static int lochnagar_clk_probe(struct platform_device *pdev)
 {
 	struct clk_init_data clk_init = {
 		.ops = &lochnagar_clk_ops,
+		.flags = CLK_SET_RATE_NO_REPARENT,
 	};
 	struct device *dev = &pdev->dev;
 	struct lochnagar_clk_priv *priv;