Message-ID: <9f3988fc28a7a113661ec27a9cf5984a29751ede.camel@analog.com>
Date:   Fri, 8 Nov 2019 07:10:29 +0000
From:   "Ardelean, Alexandru" <alexandru.Ardelean@...log.com>
To:     "linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "sboyd@...nel.org" <sboyd@...nel.org>,
        "geert+renesas@...der.be" <geert+renesas@...der.be>
CC:     "Hennerich, Michael" <Michael.Hennerich@...log.com>,
        "jsarha@...com" <jsarha@...com>, "ce3a@....de" <ce3a@....de>,
        "mturquette@...libre.com" <mturquette@...libre.com>
Subject: Re: [PATCH] clk: clk-gpio: Add dt option to propagate rate change to
 parent

On Fri, 2019-11-08 at 06:50 +0000, Ardelean, Alexandru wrote:
> [External]
> 
> On Thu, 2019-11-07 at 14:53 -0800, Stephen Boyd wrote:
> > Quoting Ardelean, Alexandru (2019-11-07 05:25:38)
> > > 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@...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
> > > 
> > > 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.
> > 
> > I think we can just add CLK_SET_RATE_PARENT for all gpio gate clks then
> > and you'll be happy? Care to send that patch and Cc Geert and other
> > Renesas maintainers? That avoids any DT property and should be fine for
> > anyone as far as I can tell. Maybe the inverse will be desired, but not
> > wanting rate to propagate is an edge case that we may want to call out
> > explicitly in DT at some point in the future, but shouldn't worry about
> > until then.
> > 
> 
> Will resend, thanks.
> Geert is CC-ed here as well [unless there is another Geert].

Oh right.
You CC-ed Geert this time. I assumed that I did, from the get_maintainers
script. It's still seems like black-art trying to see how tag people when
sending patches. Especially if you're new.

> 
> I'll send a V2 in-reply-to this thread.
> 
> Thanks
> Alex

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