| Message ID | 20221018-clk-range-checks-fixes-v2-20-f6736dec138e@cerno.tech (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | clk: Make determine_rate mandatory for muxes | expand |
On Fri, Nov 04, 2022 at 02:17:37PM +0100, Maxime Ripard wrote: > The WM381x "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. > Yeah I don't think there would be anything wrong with this clock changing parents on a rate change, but as you say this can be refined down the line if someone needs the behaviour. It's an older part so probably better to stick roughly to the current behaviour for now. Acked-by: Charles Keepax <ckeepax@opensource.cirrus.com> Thanks, Charles
diff --git a/drivers/clk/clk-wm831x.c b/drivers/clk/clk-wm831x.c index ae6dd38ec053..be3a9c1f3610 100644 --- a/drivers/clk/clk-wm831x.c +++ b/drivers/clk/clk-wm831x.c @@ -329,6 +329,7 @@ static const struct clk_ops wm831x_clkout_ops = { .is_prepared = wm831x_clkout_is_prepared, .prepare = wm831x_clkout_prepare, .unprepare = wm831x_clkout_unprepare, + .determine_rate = __clk_mux_determine_rate, .get_parent = wm831x_clkout_get_parent, .set_parent = wm831x_clkout_set_parent, }; @@ -338,7 +339,7 @@ static const struct clk_init_data wm831x_clkout_init = { .ops = &wm831x_clkout_ops, .parent_names = wm831x_clkout_parents, .num_parents = ARRAY_SIZE(wm831x_clkout_parents), - .flags = CLK_SET_RATE_PARENT, + .flags = CLK_SET_RATE_PARENT | CLK_SET_RATE_NO_REPARENT, }; static int wm831x_clk_probe(struct platform_device *pdev)
The WM381x "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. Signed-off-by: Maxime Ripard <maxime@cerno.tech> --- drivers/clk/clk-wm831x.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)