linux-kernel - Re: [PATCH V4 RESEND 1/2] dt-bindings/irq: add binding for NXP INTMUX interrupt multiplexer

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Message-ID: <CAL_Jsq++ZtPCV58eg-O5t2+L82MCsX8Tp262nsO4mNykVZmxYw@mail.gmail.com>
Date:   Tue, 14 Jan 2020 08:11:58 -0600
From:   Rob Herring <robh@...nel.org>
To:     Joakim Zhang <qiangqing.zhang@....com>
Cc:     "maz@...nel.org" <maz@...nel.org>,
        "jason@...edaemon.net" <jason@...edaemon.net>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        dl-linux-imx <linux-imx@....com>, Andy Duan <fugang.duan@....com>
Subject: Re: [PATCH V4 RESEND 1/2] dt-bindings/irq: add binding for NXP INTMUX
 interrupt multiplexer

On Tue, Jan 14, 2020 at 2:22 AM Joakim Zhang <qiangqing.zhang@....com> wrote:
>
>
> > -----Original Message-----
> > From: Joakim Zhang <qiangqing.zhang@....com>
> > Sent: 2020年1月14日 10:44
> > To: Rob Herring <robh@...nel.org>
> > Cc: maz@...nel.org; jason@...edaemon.net; tglx@...utronix.de;
> > mark.rutland@....com; shawnguo@...nel.org; s.hauer@...gutronix.de;
> > kernel@...gutronix.de; festevam@...il.com; linux-kernel@...r.kernel.org;
> > devicetree@...r.kernel.org; linux-arm-kernel@...ts.infradead.org; dl-linux-imx
> > <linux-imx@....com>; Andy Duan <fugang.duan@....com>
> > Subject: RE: [PATCH V4 RESEND 1/2] dt-bindings/irq: add binding for NXP
> > INTMUX interrupt multiplexer
> >
> >
> > > -----Original Message-----
> > > From: Rob Herring <robh@...nel.org>
> > > Sent: 2020年1月14日 5:04
> > > To: Joakim Zhang <qiangqing.zhang@....com>
> > > Cc: maz@...nel.org; jason@...edaemon.net; tglx@...utronix.de;
> > > mark.rutland@....com; shawnguo@...nel.org; s.hauer@...gutronix.de;
> > > kernel@...gutronix.de; festevam@...il.com;
> > > linux-kernel@...r.kernel.org; devicetree@...r.kernel.org;
> > > linux-arm-kernel@...ts.infradead.org; dl-linux-imx
> > > <linux-imx@....com>; Andy Duan <fugang.duan@....com>
> > > Subject: Re: [PATCH V4 RESEND 1/2] dt-bindings/irq: add binding for
> > > NXP INTMUX interrupt multiplexer
> > >
> > > On Mon, Jan 13, 2020 at 03:08:40PM +0800, Joakim Zhang wrote:
> > > > This patch adds the DT bindings for the NXP INTMUX interrupt
> > > > multiplexer for i.MX8 family SoCs.
> > > >
> > > > Signed-off-by: Joakim Zhang <qiangqing.zhang@....com>
> > > > ---
> > > >  .../interrupt-controller/fsl,intmux.yaml      | 77
> > +++++++++++++++++++
> > > >  1 file changed, 77 insertions(+)
> > > >  create mode 100644
> > > > Documentation/devicetree/bindings/interrupt-controller/fsl,intmux.ya
> > > > ml
> > >
> > > Please run 'make dt_binding_check' and fix the errors:
> > >
> > > Documentation/devicetree/bindings/interrupt-controller/fsl,intmux.yaml:
> > > while scanning for the next token found character that cannot start any token
> > >   in "<unicode string>", line 60, column 1
> > Got it. Will keep in mind. Thanks.
> >
> > > >
> > > > diff --git
> > > > a/Documentation/devicetree/bindings/interrupt-controller/fsl,intmux.
> > > > ya
> > > > ml
> > > > b/Documentation/devicetree/bindings/interrupt-controller/fsl,intmux.
> > > > ya
> > > > ml
> > > > new file mode 100644
> > > > index 000000000000..4dba532fe0bd
> > > > --- /dev/null
> > > > +++ b/Documentation/devicetree/bindings/interrupt-controller/fsl,int
> > > > +++ mu
> > > > +++ x.yaml
> > > > @@ -0,0 +1,77 @@
> > > > +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause) %YAML 1.2
> > > > +---
> > > > +$id:
> > > > +https://eur01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fde
> > > > +vi
> > > >
> > >
> > +cetree.org%2Fschemas%2Finterrupt-controller%2Ffsl%2Cintmux.yaml%23&a
> > > m
> > > >
> > >
> > +p;data=02%7C01%7Cqiangqing.zhang%40nxp.com%7Cdc2443dc111149805c7
> > > 208d7
> > > >
> > >
> > +986c157f%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C63714546
> > > 2291934
> > > >
> > >
> > +492&amp;sdata=Ao4iuj2D48KAeC%2FvQvJqUUxGJEjSY0HyL5ZlT2XrSrg%3D&
> > > amp;re
> > > > +served=0
> > > > +$schema:
> > > > +https://eur01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fde
> > > > +vi
> > > >
> > >
> > +cetree.org%2Fmeta-schemas%2Fcore.yaml%23&amp;data=02%7C01%7Cqia
> > > ngqing
> > > >
> > >
> > +.zhang%40nxp.com%7Cdc2443dc111149805c7208d7986c157f%7C686ea1d3b
> > > c2b4c6
> > > >
> > >
> > +fa92cd99c5c301635%7C0%7C0%7C637145462291934492&amp;sdata=YoHb
> > > TO5C8Nlq
> > > > +YYoWTNufaIxnvdtPUZaKzvwK49I9Zdc%3D&amp;reserved=0
> > > > +
> > > > +title: Freescale INTMUX interrupt multiplexer
> > > > +
> > > > +maintainers:
> > > > +  - Marc Zyngier <maz@...nel.org>
> > > > +
> > > > +properties:
> > > > +  compatible:
> > > > +    items:
> > > > +      const: fsl,imx-intmux
> > > > +
> > > > +  reg:
> > > > +    maxItems: 1
> > > > +
> > > > +  interrupts:
> > > > +    minItems: 1
> > > > +    maxItems: 8
> > > > +    description: |
> > > > +      Should contain the parent interrupt lines (up to 8) used to multiplex
> > > > +      the input interrupts.
> > > > +
> > > > +  interrupt-controller: true
> > > > +
> > > > +  '#interrupt-cells':
> > > > +    const: 2
> > > > +
> > > > +  clocks:
> > > > +    maxItems: 1
> > > > +    description: ipg clock.
> > > > +
> > > > +  clock-names:
> > > > +    items:
> > > > +      const: ipg
> > > > +
> > > > +  fsl,intmux_chans:
> > >
> > > Don't use '_' in property names.
> > Got it.
> >
> > > Is this any different from the length of 'interrupts' which you can count?
> > A bit different. Such as, the length of 'interrupts' is 8, but we can set
> > fsl,intmux_chans value is 4. That means there are 8 channels, but actually we
> > only use 4 channels.
> > If you think this make no sense, due to we can assign 4 items for 'interrupts' to
> > get the same result. So we can count the length of 'interrupts' to get the
> > channels configured, then this property is no need.
> > Which one do you think is better?
> >               interrupts = <GIC_SPI 16 IRQ_TYPE_LEVEL_HIGH>,
> >                            <GIC_SPI 17 IRQ_TYPE_LEVEL_HIGH>,
> >                            <GIC_SPI 18 IRQ_TYPE_LEVEL_HIGH>,
> >                            <GIC_SPI 19 IRQ_TYPE_LEVEL_HIGH>,
> >                            <GIC_SPI 20 IRQ_TYPE_LEVEL_HIGH>,
> >                            <GIC_SPI 21 IRQ_TYPE_LEVEL_HIGH>,
> >                            <GIC_SPI 22 IRQ_TYPE_LEVEL_HIGH>,
> >                            <GIC_SPI 23 IRQ_TYPE_LEVEL_HIGH>;
> >               fsl,intmux_chans = <4>;
>
> One more add, the number of channels is fixed to 8. It will make more clear to users that it supports 8 channels with 8 items for 'interrupts', and users can decide how many
> channels they use with 'fsl,intmux_chans' property.

How does one decide how many? Why would you not use as many channels
as possible (other than muxing interrupts or not doesn't really make a
bit difference in servicing overhead)?

If you wanted to configure how many parent interrupts, wouldn't you
also want to configure the routing of child interrupts to specific
parent interrupts?

So I would drop this property. You can define both how many parents
and the routing with interrupt-map property, though I would not do
that until you have a real need.

Rob