Re: [PATCH v4 45/68] rtc: sun6i: Add a determine_rate hook

["Jernej Škrabec" <jernej.skrabec@gmail.com>]

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,