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

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Date:   Mon, 28 Oct 2019 20:21:32 +0000
From:   Chris Packham <Chris.Packham@...iedtelesis.co.nz>
To:     "sbranden@...adcom.com" <sbranden@...adcom.com>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "bcm-kernel-feedback-list@...adcom.com" 
        <bcm-kernel-feedback-list@...adcom.com>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "rjui@...adcom.com" <rjui@...adcom.com>,
        "linus.walleij@...aro.org" <linus.walleij@...aro.org>
CC:     "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH 2/2] ARM: dts: NSP: avoid unnecessary probe deferrals

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@...iedtelesis.co.nz>
> > ---
> >  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@...c0 {
> > +			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@...c0 {
> > -			compatible = "brcm,nsp-pinmux";
> > -			reg = <0x3f1c0 0x04>,
> > -			      <0x30028 0x04>,
> > -			      <0x3f408 0x04>;
> > -		};
> > -
> >  		thermal: thermal@...c0 {
> >  			compatible = "brcm,ns-thermal";
> >  			reg = <0x3f2c0 0x10>;
> > 
> 
>