linux-kernel - Re: [PATCH] clk: clk-gpio: Add dt option to propagate rate change to parent

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Date:   Wed, 06 Nov 2019 14:43:05 -0800
From:   Stephen Boyd <sboyd@...nel.org>
To:     Alexandru Ardelean <alexandru.ardelean@...log.com>,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     mturquette@...libre.com, jsarha@...com, ce3a@....de,
        Michael Hennerich <michael.hennerich@...log.com>,
        Alexandru Ardelean <alexandru.ardelean@...log.com>
Subject: Re: [PATCH] clk: clk-gpio: Add dt option to propagate rate change to parent

Quoting Alexandru Ardelean (2019-11-06 03:35:51)
> From: Michael Hennerich <michael.hennerich@...log.com>
> 
> For certain setups/boards it's useful to propagate the rate change of the
> clock up one level to the parent clock.
> 
> This change implements this by defining a `clk-set-rate-parent` device-tree
> property which sets the `CLK_SET_RATE_PARENT` flag to the clock (when set).
> 
> Signed-off-by: Michael Hennerich <michael.hennerich@...log.com>
> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@...log.com>
> ---
>  drivers/clk/clk-gpio.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/clk/clk-gpio.c b/drivers/clk/clk-gpio.c
> index 9d930edd6516..6dfbc4b952fe 100644
> --- a/drivers/clk/clk-gpio.c
> +++ b/drivers/clk/clk-gpio.c
> @@ -241,6 +241,7 @@ static int gpio_clk_driver_probe(struct platform_device *pdev)
>         struct device_node *node = pdev->dev.of_node;
>         const char **parent_names, *gpio_name;
>         unsigned int num_parents;
> +       unsigned long clk_flags;
>         struct gpio_desc *gpiod;
>         struct clk *clk;
>         bool is_mux;
> @@ -274,13 +275,16 @@ static int gpio_clk_driver_probe(struct platform_device *pdev)
>                 return ret;
>         }
>  
> +       clk_flags = of_property_read_bool(node, "clk-set-rate-parent") ?
> +                       CLK_SET_RATE_PARENT : 0;

Is there a DT binding update somewhere? It looks like a linux-ism from
the DT perspective. I wonder if we can somehow figure out that it's OK
to call clk_set_rate() on the parent here? Or is it safe to assume that
we can just always call set rate on the parent? I think for a gate it's
good and we can just do so, but for a mux maybe not. Care to describe
your scenario a little more so we can understand why you want to set
this flag? Is it for a mux or a gate type gpio?