Messages in this thread | | | From | "Ardelean, Alexandru" <> | Subject | Re: [PATCH] clk: clk-gpio: Add dt option to propagate rate change to parent | Date | Thu, 7 Nov 2019 13:25:38 +0000 |
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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.
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