diff mbox series

[v2,13/65] clk: lmk04832: clkout: Add a determine_rate hook

Message ID 20221018-clk-range-checks-fixes-v2-13-f6736dec138e@cerno.tech
State Superseded
Headers show
Series clk: Make determine_rate mandatory for muxes | expand

Commit Message

Maxime Ripard Nov. 4, 2022, 1:17 p.m. UTC
The LKM04832 "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.

Since the CLK_SET_RATE_NO_REPARENT flag was already set though, it seems
unlikely.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
---
 drivers/clk/clk-lmk04832.c | 1 +
 1 file changed, 1 insertion(+)

Comments

Liam Beguin Nov. 13, 2022, 10:35 p.m. UTC | #1
Hi Maxime,

On Fri, Nov 04, 2022 at 02:17:30PM +0100, Maxime Ripard wrote:
> The LKM04832 "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().

This is correct, the set_parent hook is effectively unused at the
moment. It was implemented as a way for consumers to select the parent
themselves.

The LMK04832 is used in JESD204 applications where devices need a device
clock as well as a sysref clock. Since this is determined by the
hardware layout, a devicetree option is used to select the inital state
of the clkout mux. This is set at the end of lmk04832_register_clkout().

> 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.
> 
> Since the CLK_SET_RATE_NO_REPARENT flag was already set though, it seems
> unlikely.
> 
> Signed-off-by: Maxime Ripard <maxime@cerno.tech>

Reviewed-by: Liam Beguin <liambeguin@gmail.com>

Cheers,
Liam

> ---
>  drivers/clk/clk-lmk04832.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/clk/clk-lmk04832.c b/drivers/clk/clk-lmk04832.c
> index f416f8bc2898..f68bb0affdad 100644
> --- a/drivers/clk/clk-lmk04832.c
> +++ b/drivers/clk/clk-lmk04832.c
> @@ -1281,6 +1281,7 @@ static const struct clk_ops lmk04832_clkout_ops = {
>  	.is_enabled = lmk04832_clkout_is_enabled,
>  	.prepare = lmk04832_clkout_prepare,
>  	.unprepare = lmk04832_clkout_unprepare,
> +	.determine_rate = __clk_mux_determine_rate,
>  	.set_parent = lmk04832_clkout_set_parent,
>  	.get_parent = lmk04832_clkout_get_parent,
>  };
> 
> -- 
> b4 0.11.0-dev-99e3a
>
diff mbox series

Patch

diff --git a/drivers/clk/clk-lmk04832.c b/drivers/clk/clk-lmk04832.c
index f416f8bc2898..f68bb0affdad 100644
--- a/drivers/clk/clk-lmk04832.c
+++ b/drivers/clk/clk-lmk04832.c
@@ -1281,6 +1281,7 @@  static const struct clk_ops lmk04832_clkout_ops = {
 	.is_enabled = lmk04832_clkout_is_enabled,
 	.prepare = lmk04832_clkout_prepare,
 	.unprepare = lmk04832_clkout_unprepare,
+	.determine_rate = __clk_mux_determine_rate,
 	.set_parent = lmk04832_clkout_set_parent,
 	.get_parent = lmk04832_clkout_get_parent,
 };