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From:   Rob Herring <robh@kernel.org>
Date:   Thu, 3 Mar 2022 13:06:27 -0600
Message-ID: <CAL_JsqL_02Gw6hw59NdH_rCDmwy5f+OrCsifmuNkxo2OgTYnYg@mail.gmail.com>
Subject: Re: [PATCH] dt-bindings: serial: fsl-lpuart: Add imx93 compatible string
To:     Peng Fan <peng.fan@nxp.com>
Cc:     "Peng Fan (OSS)" <peng.fan@oss.nxp.com>,
        "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
        "linux-serial@vger.kernel.org" <linux-serial@vger.kernel.org>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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On Sun, Feb 27, 2022 at 6:44 PM Peng Fan <peng.fan@nxp.com> wrote:
>
> Hi Rob,
>
> > Subject: Re: [PATCH] dt-bindings: serial: fsl-lpuart: Add imx93 compatible
> > string
> >
> > On Tue, Feb 15, 2022 at 04:13:34PM +0800, Peng Fan (OSS) wrote:
> > > From: Peng Fan <peng.fan@nxp.com>
> > >
> > > The lpuart on i.MX93 is derived from i.MX8ULP with some industrial
> > > enhancements, it uses three compatible strings, so update the
> >
> > Looks like it's 2 compatible strings...
>
> Oh, yes. i.MX8ULP/7ULP is same uart IP.
>
> >
> > > compatible string for i.MX93. But for a few instants,
> >
> > s/instants/instances/
> >
> > > DTR_B, DSR_B, DCD_B and RIN_B pins are supported, so use one
> > > compatible string fsl,imx93-lpuart-v2
> >
> > If the differences are just what gets pinned out, then I think the differences
> > should be handled with separate properties. We probably already have some.
> >
> > Plus, while you may have all the above signals, a board design may still only
> > use a subset.
>
> It is SoC integration level with above features not support in some instances,
> so no such signals connected to SoC pin.
>
> Saying LPUART IP itself support DTR/DSR/DCD/RIN, but instance A has the
> feature disabled when doing SoC integration, instance B has the feature enabled
> when doing SoC integration. What's your suggestion with such case?

Unless it changes the register interface in a non-compatible way that
the driver needs to know about, I would not do a different compatible.
For example, register offsets change.

Rob