| 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| State | Superseded |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 |
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 --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, };
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(+)