linux-kernel - RE: [PATCH 4/4] ARM64: dts: imx: add i.MX8QXP system controller RTC support

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Message-ID: <DB3PR0402MB39164C9E9A7DC29C6D451AC0F5D10@DB3PR0402MB3916.eurprd04.prod.outlook.com>
Date:   Wed, 28 Nov 2018 10:03:01 +0000
From:   Anson Huang <anson.huang@....com>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>
CC:     Lothar Wa��mann <LW@...O-electronics.de>,
        "a.zummo@...ertech.it" <a.zummo@...ertech.it>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "will.deacon@....com" <will.deacon@....com>,
        Aisheng DONG <aisheng.dong@....com>,
        Andy Gross <andy.gross@...aro.org>,
        "arnd@...db.de" <arnd@...db.de>,
        "horms+renesas@...ge.net.au" <horms+renesas@...ge.net.au>,
        "heiko@...ech.de" <heiko@...ech.de>,
        "bjorn.andersson@...aro.org" <bjorn.andersson@...aro.org>,
        "enric.balletbo@...labora.com" <enric.balletbo@...labora.com>,
        "amit.kucheria@...aro.org" <amit.kucheria@...aro.org>,
        "ezequiel@...labora.com" <ezequiel@...labora.com>,
        "olof@...om.net" <olof@...om.net>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "linux-rtc@...r.kernel.org" <linux-rtc@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        dl-linux-imx <linux-imx@....com>
Subject: RE: [PATCH 4/4] ARM64: dts: imx: add i.MX8QXP system controller RTC
 support



Best Regards!
Anson Huang

> -----Original Message-----
> From: Alexandre Belloni [mailto:alexandre.belloni@...tlin.com]
> Sent: 2018年11月28日 17:58
> To: Anson Huang <anson.huang@....com>
> Cc: Lothar Wa��mann <LW@...O-electronics.de>; a.zummo@...ertech.it;
> robh+dt@...nel.org; mark.rutland@....com; catalin.marinas@....com;
> will.deacon@....com; Aisheng DONG <aisheng.dong@....com>; Andy Gross
> <andy.gross@...aro.org>; arnd@...db.de; horms+renesas@...ge.net.au;
> heiko@...ech.de; bjorn.andersson@...aro.org; enric.balletbo@...labora.com;
> amit.kucheria@...aro.org; ezequiel@...labora.com; olof@...om.net;
> shawnguo@...nel.org; linux-rtc@...r.kernel.org; devicetree@...r.kernel.org;
> linux-kernel@...r.kernel.org; linux-arm-kernel@...ts.infradead.org;
> dl-linux-imx <linux-imx@....com>
> Subject: Re: [PATCH 4/4] ARM64: dts: imx: add i.MX8QXP system controller
> RTC support
> 
> On 28/11/2018 09:41:22+0000, Anson Huang wrote:
> > > > i.MX SoCs ONLY have 1 RTC. And RTC are always enabled by default
> > > > for all i.MX SoCs, so do we have to disable it here and enable it in board
> dts?
> > > >
> > >
> > > I would say that most of the i.MX based boards include another RTC
> > > because the SoC one consumes way too much power.
> > >
> > > Note that I don't care too much whether it is enabled by default, I
> > > was simply explaining why you may want to disable it by default.
> >
> > OK, this system controller RTC is a little different, it is controlled
> > by system controller firmware, and system controller firmware will
> > always select the best one for its user(Linux kernel) if there are other RTCs
> available, so I think we can keep it enabled by default for now. Thanks.
> >
> 
> Do you mean that the plan is to push support for the external RTCs (e.g.
> the i2c ones) to the M4 firmware?

As far as I know, currently there is no such plan/support in system controller (M4) firmware,
and if there are external RTCs, like some PMICs have RTC inside, yes, M4 will
control it and Linux kernel (AP) does NOT need to care about which RTC is used,
same IPC API will be used I think.

Anson.

> 
> --
> Alexandre Belloni, Bootlin
> Embedded Linux and Kernel engineering
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