On Wed, Jul 27, 2016 at 3:30 PM, Maxime Ripard <maxime.ripard@xxxxxxxxxxxxxxxxxx> wrote: > On Tue, Jul 26, 2016 at 03:04:29PM +0800, Chen-Yu Tsai wrote: >> On sunxi we support cpufreq by changing the clock rate of PLL-CPU. >> It's possible the clock output of the PLL goes out of the CPU's >> operational limits when the PLL's multipliers / dividers are changed >> and it hasn't stabilized yet. This would result in the CPU hanging. >> >> To circumvent this, we temporarily switch the CPU mux clock to another >> stable clock before the rate change, and switch it back after the PLL >> stabilizes. This is done with clk notifiers registered on the PLL. >> >> This patch adds common functions for notifiers to reparent mux clocks. >> >> Signed-off-by: Chen-Yu Tsai <wens@xxxxxxxx> >> --- >> drivers/clk/sunxi-ng/ccu_mux.c | 36 ++++++++++++++++++++++++++++++++++++ >> drivers/clk/sunxi-ng/ccu_mux.h | 14 ++++++++++++++ >> 2 files changed, 50 insertions(+) >> >> diff --git a/drivers/clk/sunxi-ng/ccu_mux.c b/drivers/clk/sunxi-ng/ccu_mux.c >> index f96eabb5d1f3..8a6e9065cb85 100644 >> --- a/drivers/clk/sunxi-ng/ccu_mux.c >> +++ b/drivers/clk/sunxi-ng/ccu_mux.c >> @@ -8,7 +8,9 @@ >> * the License, or (at your option) any later version. >> */ >> >> +#include <linux/clk.h> >> #include <linux/clk-provider.h> >> +#include <linux/delay.h> >> >> #include "ccu_gate.h" >> #include "ccu_mux.h" >> @@ -199,3 +201,37 @@ const struct clk_ops ccu_mux_ops = { >> .determine_rate = __clk_mux_determine_rate, >> .recalc_rate = ccu_mux_recalc_rate, >> }; >> + >> +/* >> + * This clock notifier is called when the frequency of the of the parent >> + * PLL clock is to be changed. The idea is to switch the parent to a >> + * stable clock, such as the main oscillator, while the PLL frequency >> + * stabilizes. >> + */ >> +static int ccu_mux_notifier_cb(struct notifier_block *nb, >> + unsigned long event, void *data) >> +{ >> + struct ccu_mux_nb *mux = to_ccu_mux_nb(nb); >> + int ret = 0; >> + >> + if (event == PRE_RATE_CHANGE) { >> + mux->original_index = ccu_mux_helper_get_parent(mux->common, >> + mux->cm); >> + ret = ccu_mux_helper_set_parent(mux->common, mux->cm, >> + mux->bypass_index); >> + } else if (event == POST_RATE_CHANGE) { >> + ret = ccu_mux_helper_set_parent(mux->common, mux->cm, >> + mux->original_index); >> + } >> + >> + udelay(mux->delay_us); > > Are you sure we need that delay? > > set_rate will end and notify you once the PLL rate is stable, so it > looks redundant. The delay requirement is on the cpu mux clk, not the PLL. The datasheet says you should wait for up to 8 clock cycles after changing the parent. Not sure how this factors with the CPU actually doing the waiting though. So this is separate from the PLL lock delay. ChenYu -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html