Re: [PATCH 2/2] ARM: dts: NSP: avoid unnecessary probe deferrals

From: Chris Packham
Date: Mon Oct 28 2019 - 16:21:40 EST


On Fri, 2019-10-25 at 10:26 -0700, Florian Fainelli wrote:
> On 10/24/19 9:00 PM, Chris Packham wrote:
> > The pinctrl node is used by the gpioa node. Which may have more
> > descendants at a board level. If the pinctrl node isn't probed first the
> > gpio is deferred and anything that needs a gpio pin on that chip is also
> > deferred.
>
> If what you care is to optimize your boot flow such that no re-probing
> occurs, maybe another solution to look at is to re-order the order in
> which subsystems are initialized or built (_initcall changes or
> drivers/Makefile changes), because changing Device Tree certainly does
> not scale over platforms and I recall Rob indicating that he wanted to
> introduce randomized platform_device creation from
> of_platform_bus_populate() at one point or another.
>

Hmm. I might be missing something. pinctrl-nsp-gpio.c uses
arch_initcall_sync() and pinctrl-nsp-mux.c uses arch_initcall() so in
theory they are already in the right order.

> >
> > Normally we and nodes in the device tree to be listed in their natural
> > memory mapped address order but putting the pinctrl node first avoids
> > the deferral of numerous devices so make an exception in this case.
>
> That is a workaround more than a real solution, though I understand why
> you would to do that. One downside is that the entries are no longer in
> incrementing register address order and that is visually disturbing and
> who knows, maybe a drive by contributor whose pet project will be to
> order the Device Tree entries by incrementing addresses will change that
> in the future...
>

I guess really what's needed is something that understands phandles and
tries to produce a dependency tree based on that.

> >
> > Signed-off-by: Chris Packham <chris.packham@xxxxxxxxxxxxxxxxxxx>
> > ---
> > arch/arm/boot/dts/bcm-nsp.dtsi | 14 +++++++-------
> > 1 file changed, 7 insertions(+), 7 deletions(-)
> >
> > diff --git a/arch/arm/boot/dts/bcm-nsp.dtsi b/arch/arm/boot/dts/bcm-nsp.dtsi
> > index da6d70f09ef1..dd7a65743c08 100644
> > --- a/arch/arm/boot/dts/bcm-nsp.dtsi
> > +++ b/arch/arm/boot/dts/bcm-nsp.dtsi
> > @@ -172,6 +172,13 @@
> > #address-cells = <1>;
> > #size-cells = <1>;
> >
> > + pinctrl: pinctrl@3f1c0 {
> > + compatible = "brcm,nsp-pinmux";
> > + reg = <0x3f1c0 0x04>,
> > + <0x30028 0x04>,
> > + <0x3f408 0x04>;
> > + };
> > +
> > gpioa: gpio@20 {
> > compatible = "brcm,nsp-gpio-a";
> > reg = <0x0020 0x70>,
> > @@ -458,13 +465,6 @@
> > "sata2";
> > };
> >
> > - pinctrl: pinctrl@3f1c0 {
> > - compatible = "brcm,nsp-pinmux";
> > - reg = <0x3f1c0 0x04>,
> > - <0x30028 0x04>,
> > - <0x3f408 0x04>;
> > - };
> > -
> > thermal: thermal@3f2c0 {
> > compatible = "brcm,ns-thermal";
> > reg = <0x3f2c0 0x10>;
> >
>
>