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From:   Rob Herring <robh@kernel.org>
Date:   Tue, 14 Jan 2020 08:39:19 -0600
Message-ID: <CAL_JsqLsQmvM0Qsspj5n+1iy5X0TXaULonGtjKRkdOoSQVQmzw@mail.gmail.com>
Subject: Re: [PATCH] ARM: dts: imx: drop "fsl,aips-bus"
To:     Peng Fan <peng.fan@nxp.com>
Cc:     "mark.rutland@arm.com" <mark.rutland@arm.com>,
        "shawnguo@kernel.org" <shawnguo@kernel.org>,
        "kernel@pengutronix.de" <kernel@pengutronix.de>,
        "festevam@gmail.com" <festevam@gmail.com>,
        dl-linux-imx <linux-imx@nxp.com>,
        Aisheng Dong <aisheng.dong@nxp.com>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Alice Guo <alice.guo@nxp.com>
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On Sun, Jan 5, 2020 at 8:38 PM Peng Fan <peng.fan@nxp.com> wrote:
>
> Hi Rob,
>
> > Subject: Re: [PATCH] ARM: dts: imx: drop "fsl,aips-bus"
> >
> > On Mon, Dec 30, 2019 at 08:58:05AM +0000, Peng Fan wrote:
> > > From: Peng Fan <peng.fan@nxp.com>
> > >
> > > There is no binding doc for "fsl,aips-bus", "simple-bus" is enough for
> > > aips usage, so drop it.
> >
> > NAK. The AIPS bus has registers, so 'simple-bus' alone is not enough.
>
> You mean the "reg" property below, right?
>                 aips-bus@2000000 { /* AIPS1 */
> -                       compatible = "fsl,aips-bus", "simple-bus";
> +                       compatible = "simple-bus";
>                         #address-cells = <1>;
>                         #size-cells = <1>;
>                         reg = <0x02000000 0x100000>;
>
> But the reg property is not required, I think it could be removed.
> There is no binding doc and driver for "fsl,aips-bus", so I think
> It not make sense to have that compatible in dts.

Well, there should be a binding doc, but whether or not there's a
driver is irrelevant.

From what I remember, either AIPS or SPBA bus has registers to allow
user mode access or not. Something may need to configure those and it
may want to use DT info to do that. It's not just Linux that you need
to think about.

Rob