Re: [PATCH v3 29/65] clk: socfpga: gate: Add a determine_rate hook

Dinh Nguyen
2023-04-24T18:32:35Z

Hi Maxime,

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@cerno.tech>
> ---
> 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.

Dinh