Hi Dinh, On Thu, Apr 27, 2023 at 02:09:48PM -0500, Dinh Nguyen wrote: > Hi Maxime, > > On 4/25/23 09:48, Maxime Ripard wrote: > > Hi Dinh, > > > > On Mon, Apr 24, 2023 at 01:32:28PM -0500, Dinh Nguyen wrote: > > > On 4/4/23 05:11, Maxime Ripard wrote: > > > > The SoCFGPA gate 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@xxxxxxxxxx> > > > > --- > > > > drivers/clk/socfpga/clk-gate.c | 3 ++- > > > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/drivers/clk/socfpga/clk-gate.c b/drivers/clk/socfpga/clk-gate.c > > > > index 32ccda960f28..cbba8462a09e 100644 > > > > --- a/drivers/clk/socfpga/clk-gate.c > > > > +++ b/drivers/clk/socfpga/clk-gate.c > > > > @@ -110,6 +110,7 @@ static unsigned long socfpga_clk_recalc_rate(struct clk_hw *hwclk, > > > > static struct clk_ops gateclk_ops = { > > > > .recalc_rate = socfpga_clk_recalc_rate, > > > > + .determine_rate = __clk_mux_determine_rate, > > > > .get_parent = socfpga_clk_get_parent, > > > > .set_parent = socfpga_clk_set_parent, > > > > }; > > > > @@ -166,7 +167,7 @@ void __init socfpga_gate_init(struct device_node *node) > > > > init.name = clk_name; > > > > init.ops = ops; > > > > - init.flags = 0; > > > > + init.flags = CLK_SET_RATE_NO_REPARENT; > > > > init.num_parents = of_clk_parent_fill(node, parent_name, SOCFPGA_MAX_PARENTS); > > > > if (init.num_parents < 2) { > > > > > > > > > > This patch broke SoCFPGA boot serial port. The characters are mangled. > > > > Do you have any other access to that board? If so, could you dump > > clk_summary in debugfs with and without that patch? > > > > That dump from the clk_summary are identical for both cases. Thanks for testing I'm a bit confused, there should be no difference in behaviour, and if there was any difference I would expect the clock tree to be somewhat different. Could you still paste the clk_summary (and dmesg) output? Which UART driver is being used? Also, is there a way for me to test it somehow? Thanks, Maxime
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