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

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Date:   Mon, 2 Jul 2018 00:53:50 +0000
From:   Anson Huang <anson.huang@....com>
To:     Fabio Estevam <festevam@...il.com>, Shawn Guo <shawnguo@...nel.org>
CC:     Robin Gong <yibin.gong@....com>,
        Mark Rutland <mark.rutland@....com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        dl-linux-imx <linux-imx@....com>,
        Sascha Hauer <kernel@...gutronix.de>,
        Fabio Estevam <fabio.estevam@....com>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: RE: [PATCH v1] ARM: dts: imx6sl-evk: keep sw4 always on



Anson Huang
Best Regards!


> -----Original Message-----
> From: Fabio Estevam [mailto:festevam@...il.com]
> Sent: Monday, July 2, 2018 7:33 AM
> To: Shawn Guo <shawnguo@...nel.org>; Anson Huang
> <anson.huang@....com>
> Cc: Robin Gong <yibin.gong@....com>; Mark Rutland
> <mark.rutland@....com>; open list:OPEN FIRMWARE AND FLATTENED
> DEVICE TREE BINDINGS <devicetree@...r.kernel.org>; linux-kernel
> <linux-kernel@...r.kernel.org>; Rob Herring <robh+dt@...nel.org>;
> dl-linux-imx <linux-imx@....com>; Sascha Hauer <kernel@...gutronix.de>;
> Fabio Estevam <fabio.estevam@....com>; moderated list:ARM/FREESCALE
> IMX / MXC ARM ARCHITECTURE <linux-arm-kernel@...ts.infradead.org>
> Subject: Re: [PATCH v1] ARM: dts: imx6sl-evk: keep sw4 always on
> 
> On Sun, Jul 1, 2018 at 6:34 AM, Shawn Guo <shawnguo@...nel.org> wrote:
> > On Mon, Jun 25, 2018 at 08:34:11PM +0800, Robin Gong wrote:
> >> SW4 is one power rail for LPDDR2 on i.mx6sl-evk, so it should be kept
> >> always on. But it's disabled after switch disabled interface
> >> implemented in pfuze driver 'commit 5fe156f1cab4
> >> ("regulator: pfuze100: add enable/disable for switch")'.Thus, it
> >> breaks kernel bootup. Add 'regulator-always-on' for SW4.
> >>
> >> Signed-off-by: Robin Gong <yibin.gong@....com>
> >
> > Does that mean boards with existing DTB installed will stop working
> > with new kernel?  That's bad, and the kernel commit should probably be
> > reverted.
> 
> Yes, this is a good point.
> 
> Anson,
> 
> Should 5fe156f1cab4 ("regulator: pfuze100: add enable/disable for
> switch") be reverted to avoid such breakage?
 
Yes, I think we can revert it to avoid breakage. Didn't notice that some
i.MX platform do NOT have those critical switches always-on.

Anson.