linux-kernel - RE: [PATCH v1] ARM: dts: imx6sl-evk: keep sw4 always on

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Date:   Tue, 3 Jul 2018 07:44:10 +0000
From:   Anson Huang <anson.huang@....com>
To:     Shawn Guo <shawnguo@...nel.org>, Robin Gong <yibin.gong@....com>
CC:     "festevam@...il.com" <festevam@...il.com>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        dl-linux-imx <linux-imx@....com>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        Fabio Estevam <fabio.estevam@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: RE: [PATCH v1] ARM: dts: imx6sl-evk: keep sw4 always on

Hi, Shawn

Anson Huang
Best Regards!


> -----Original Message-----
> From: Shawn Guo [mailto:shawnguo@...nel.org]
> Sent: Tuesday, July 3, 2018 1:39 PM
> To: Robin Gong <yibin.gong@....com>
> Cc: festevam@...il.com; Anson Huang <anson.huang@....com>;
> mark.rutland@....com; devicetree@...r.kernel.org;
> linux-kernel@...r.kernel.org; robh+dt@...nel.org; dl-linux-imx
> <linux-imx@....com>; kernel@...gutronix.de; Fabio Estevam
> <fabio.estevam@....com>; linux-arm-kernel@...ts.infradead.org
> Subject: Re: [PATCH v1] ARM: dts: imx6sl-evk: keep sw4 always on
> 
> On Mon, Jul 02, 2018 at 02:12:52AM +0000, Robin Gong wrote:
> > But in fact, the original dts is not correct without
> > 'regulator-always- on'since SW4 is the critical DDR power rail,
> > although, it's kept on in the previous kernel by no switches
> > enable/disable interfaces provided in pfuze driver. Adding new
> > property which can be done totally by the common 'regulator-always-on'
> > is not a good choice. Keep the dts patch adding 'regulator-always-on'
> > ahead of pfuze driver pach adding enable/disable interface is enough for such
> case I think.
> 
> We can not just break the installed DTBs like this.  If patching regulator driver
> with a new property is really difficult, we could migrate the existing users in a
> 'soft' way:
 
Patching regulator driver needs to add property for those regulators can be OFF,
it will make users confuse with original regulator framework knowledge, NOT a
good idea.

> 
>  - Add required regulator-always-on for regulator nodes in DTS.
 
I & Yibin already sent out patch to add " regulator-always-on " for regulator nodes in DTS,
so they can be applied first?


>  - Patch i.MX platform code to check the presence of regulator-always-on
>    property for critical regulators, and give a big warning if it's
>    missing.
It is NOT easy to identify which switch is critical or NOT, and different platforms
have different board design, it will introduce many platform specified code, so I think
just revert the pfuze100 switch enable/disable patch should be OK for now. 

>  - Wait for a couple of release cycles for users to migrate.
>  - Add regulator driver patch back and break users who keep ignoring
>    the warning.
After a couple of release cycles, add the pfuze100 switch enable/disable patch
back to support this feature, I believe users should switch to new dtb with "regulator-always-on" 
existing already.

Anson.

> 
> Shawn