From: "Ardelean, Alexandru" <alexandru.Ardelean@analog.com>
To: "linux-clk@vger.kernel.org" <linux-clk@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"sboyd@kernel.org" <sboyd@kernel.org>
Cc: "Hennerich, Michael" <Michael.Hennerich@analog.com>,
"jsarha@ti.com" <jsarha@ti.com>, "ce3a@gmx.de" <ce3a@gmx.de>,
"mturquette@baylibre.com" <mturquette@baylibre.com>
Subject: Re: [PATCH] clk: clk-gpio: Add dt option to propagate rate change to parent
Date: Thu, 7 Nov 2019 13:25:38 +0000 [thread overview]
Message-ID: <f3992013a3811ec2292e3da403841cb6e5cb95b5.camel@analog.com> (raw)
In-Reply-To: <20191106224306.A85342173E@mail.kernel.org>
On Wed, 2019-11-06 at 14:43 -0800, Stephen Boyd wrote:
> Quoting Alexandru Ardelean (2019-11-06 03:35:51)
> > From: Michael Hennerich <michael.hennerich@analog.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@analog.com>
> > Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.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
Good point. I did not think about the DT, and I guess I didn't search it
thoroughly enough. Found DT files now.
> 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?
>
For our case we are using it here [with a slight name variation in the prop
name]:
https://github.com/analogdevicesinc/linux/blob/master/arch/arm/boot/dts/zynq-adrv9361-z7035.dtsi#L43
And on this board:
https://wiki.analog.com/resources/eval/user-guides/adrv936x_rfsom/user-guide/introduction
It's for a gate-type GPIO.
The clock defined in that DT (ad9361_clkin) is attached to a clock that has
a fixed rate (xo_40mhz_fixed_clk), that can become a variable rate [from an
external source, when it is provided].
Our understanding, is that a GPIO gate clock should propagate the rate
change to the parent clock. The same goes for the GPIO MUX clock.
So, the default mode would be to always set CLK_SET_RATE_PARENT.
But, given that there are users of this driver, such a behavior change
could break other users, so we are using this DT prop.
There seems to be only one user of gpio-mux-clock in
arch/arm64/boot/dts/renesas/ulcb-kf.dtsi
Whereas for gpio-gate-clock, there are multiple users. I can't say whether
this change would break anything for them, or it would be fine.
next prev parent reply other threads:[~2019-11-07 13:25 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-06 11:35 [PATCH] clk: clk-gpio: Add dt option to propagate rate change to parent Alexandru Ardelean
2019-11-06 22:43 ` Stephen Boyd
2019-11-07 13:25 ` Ardelean, Alexandru [this message]
[not found] ` <20191107225313.4ED9D21D7B@mail.kernel.org>
2019-11-08 6:50 ` Ardelean, Alexandru
2019-11-08 7:10 ` Ardelean, Alexandru
2019-11-08 7:09 ` [PATCH v2] clk: clk-gpio: " Alexandru Ardelean
2019-11-08 7:17 ` [PATCH v3] " Alexandru Ardelean
2019-11-08 21:08 ` Stephen Boyd
2019-11-11 9:31 ` Ardelean, Alexandru
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