linux-kernel - [PATCH v3 42/65] rtc: sun6i: Add a determine

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Date:   Tue, 04 Apr 2023 12:11:32 +0200
From:   Maxime Ripard <maxime@...no.tech>
To:     Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
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Cc:     linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        linux-arm-kernel@...ts.infradead.org,
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        Maxime Ripard <maxime@...no.tech>
Subject: [PATCH v3 42/65] rtc: sun6i: Add a determine_rate hook

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 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@...no.tech>
---
 drivers/rtc/rtc-sun6i.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/rtc/rtc-sun6i.c b/drivers/rtc/rtc-sun6i.c
index dc76537f1b62..7d975202e0b9 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_mux_determine_rate,
 
 	.get_parent	= sun6i_rtc_osc_get_parent,
 	.set_parent	= sun6i_rtc_osc_set_parent,
@@ -227,6 +228,7 @@ static void __init sun6i_rtc_clk_init(struct device_node *node,
 	struct clk_init_data init = {
 		.ops		= &sun6i_rtc_osc_ops,
 		.name		= "losc",
+		.flags		= CLK_SET_RATE_NO_REPARENT,
 	};
 	const char *iosc_name = "rtc-int-osc";
 	const char *clkout_name = "osc32k-out";

-- 
2.39.2