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

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Date:   Mon, 2 Jul 2018 02:12:52 +0000
From:   Robin Gong <yibin.gong@....com>
To:     "festevam@...il.com" <festevam@...il.com>,
        Anson Huang <anson.huang@....com>
CC:     dl-linux-imx <linux-imx@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Fabio Estevam <fabio.estevam@....com>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>
Subject: Re: [PATCH v1] ARM: dts: imx6sl-evk: keep sw4 always on

On 日, 2018-07-01 at 22:17 -0300, Fabio Estevam wrote:
> On Sun, Jul 1, 2018 at 10:09 PM, Anson Huang <anson.huang@....com>
> wrote:
> 
> > 
> > On some new i.MX platforms, PFuze switches are used for supplying
> > GPU/VPU
> > or other non-critical modules only, these switches need to be
> > turned off by
> > runtime PM to avoid very high power leakage, like on mScale850D.
> Ok, in this case I suggest adding a new property so that the switches
> can be turned off only when the new property is present.
> 
> When this new property is absent, then we keep the current behavior
> and avoid dtb breakage.
> 
> Since MX8M support is not in place yet, this is not urgent, so I will
> send a revert and then you can re-work the patch so that it does not
> affect the old dtbs.
> 
> Do you agree with such approach?
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.