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

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Date:   Tue, 3 Jul 2018 13:38:45 +0800
From:   Shawn Guo <shawnguo@...nel.org>
To:     Robin Gong <yibin.gong@....com>
Cc:     "festevam@...il.com" <festevam@...il.com>,
        Anson Huang <anson.huang@....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

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:

 - Add required regulator-always-on for regulator nodes in DTS.
 - 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.
 - Wait for a couple of release cycles for users to migrate.
 - Add regulator driver patch back and break users who keep ignoring
   the warning.

Shawn