| Message ID | 20221018-clk-range-checks-fixes-v4-45-971d5077e7d2@cerno.tech (mailing list archive) |
|---|---|
| State | Accepted, archived |
| Headers | show |
| Series | clk: Make determine_rate mandatory for muxes | expand |
Dne petek, 05. maj 2023 ob 13:25:47 CEST je Maxime Ripard napisal(a): > The Allwinner sun6i RTC 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 candidates to > trigger that parent change are either the assigned-clock-parents device > tree property or 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. > > Similarly, it doesn't look like the device tree using that clock driver > uses any of the assigned-clock properties on 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 determine_rate > implementation to clk_hw_determine_rate_no_reparent(). 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. > > 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. > > Cc: Alessandro Zummo <a.zummo@towertech.it> > Cc: Alexandre Belloni <alexandre.belloni@bootlin.com> > Cc: Chen-Yu Tsai <wens@csie.org> > Cc: Jernej Skrabec <jernej.skrabec@gmail.com> > Cc: Samuel Holland <samuel@sholland.org> > Cc: linux-arm-kernel@lists.infradead.org > Cc: linux-rtc@vger.kernel.org > Cc: linux-sunxi@lists.linux.dev > Signed-off-by: Maxime Ripard <maxime@cerno.tech> Acked-by: Jernej Skrabec <jernej.skrabec@gmail.com> Best regards, Jernej > --- > drivers/rtc/rtc-sun6i.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/drivers/rtc/rtc-sun6i.c b/drivers/rtc/rtc-sun6i.c > index dc76537f1b62..71548dd59a3a 100644 > --- a/drivers/rtc/rtc-sun6i.c > +++ b/drivers/rtc/rtc-sun6i.c > @@ -214,6 +214,7 @@ static int sun6i_rtc_osc_set_parent(struct clk_hw *hw, > u8 index) > > static const struct clk_ops sun6i_rtc_osc_ops = { > .recalc_rate = sun6i_rtc_osc_recalc_rate, > + .determine_rate = clk_hw_determine_rate_no_reparent, > > .get_parent = sun6i_rtc_osc_get_parent, > .set_parent = sun6i_rtc_osc_set_parent,
diff --git a/drivers/rtc/rtc-sun6i.c b/drivers/rtc/rtc-sun6i.c index dc76537f1b62..71548dd59a3a 100644 --- a/drivers/rtc/rtc-sun6i.c +++ b/drivers/rtc/rtc-sun6i.c @@ -214,6 +214,7 @@ static int sun6i_rtc_osc_set_parent(struct clk_hw *hw, u8 index) static const struct clk_ops sun6i_rtc_osc_ops = { .recalc_rate = sun6i_rtc_osc_recalc_rate, + .determine_rate = clk_hw_determine_rate_no_reparent, .get_parent = sun6i_rtc_osc_get_parent, .set_parent = sun6i_rtc_osc_set_parent,
The Allwinner sun6i RTC 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 candidates to trigger that parent change are either the assigned-clock-parents device tree property or 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. Similarly, it doesn't look like the device tree using that clock driver uses any of the assigned-clock properties on 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 determine_rate implementation to clk_hw_determine_rate_no_reparent(). 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. 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. Cc: Alessandro Zummo <a.zummo@towertech.it> Cc: Alexandre Belloni <alexandre.belloni@bootlin.com> Cc: Chen-Yu Tsai <wens@csie.org> Cc: Jernej Skrabec <jernej.skrabec@gmail.com> Cc: Samuel Holland <samuel@sholland.org> Cc: linux-arm-kernel@lists.infradead.org Cc: linux-rtc@vger.kernel.org Cc: linux-sunxi@lists.linux.dev Signed-off-by: Maxime Ripard <maxime@cerno.tech> --- drivers/rtc/rtc-sun6i.c | 1 + 1 file changed, 1 insertion(+)