linux-kernel - RE: [RFC 1/2] dt-bindings: imx-ocotp: Add fusable-node property

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Message-ID: <AM0PR04MB4481288D0D1B8DA704FEF82B88EE0@AM0PR04MB4481.eurprd04.prod.outlook.com>
Date:   Fri, 14 Jun 2019 01:19:22 +0000
From:   Peng Fan <peng.fan@....com>
To:     Rob Herring <robh@...nel.org>
CC:     "srinivas.kandagatla@...aro.org" <srinivas.kandagatla@...aro.org>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.com>,
        dl-linux-imx <linux-imx@....com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [RFC 1/2] dt-bindings: imx-ocotp: Add fusable-node property

Hi Rob,

> Subject: Re: [RFC 1/2] dt-bindings: imx-ocotp: Add fusable-node property
> 
> On Mon, May 20, 2019 at 03:06:35AM +0000, Peng Fan wrote:
> > Introduce fusable-node property for i.MX OCOTP driver.
> > The property will only be used by Firmware(eg. U-Boot) to runtime
> > disable the nodes.
> >
> > Take i.MX6ULL for example, there are several parts that only have
> > limited modules enabled controlled by OCOTP fuse. It is not flexible
> > to provide several dts for the serval parts, instead we could provide
> > one device tree and let Firmware to runtime disable the device tree
> > nodes for those modules that are disable(fused).
> >
> > Signed-off-by: Peng Fan <peng.fan@....com>
> > ---
> >
> > Currently NXP vendor use U-Boot to set status to disabled for devices
> > that could not function,
> > https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fsour
> >
> ce.codeaurora.org%2Fexternal%2Fimx%2Fuboot-imx%2Ftree%2Farch%2Far
> m%2Fm
> >
> ach-imx%2Fmx6%2Fmodule_fuse.c%3Fh%3Dimx_v2018.03_4.14.98_2.0.0_g
> a%23n1
> >
> 49&amp;data=02%7C01%7Cpeng.fan%40nxp.com%7Ceb74876c943c4471d7f
> f08d6f05
> >
> 2fffb%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C63696063660
> 6051306&
> >
> amp;sdata=MrjCP0ufBu3uTb1ehTEu2g5eSQuYcho4UxuR9KUFEOA%3D&amp;
> reserved=
> > 0 But this approach is will not work if kernel dts node path changed.
> 
> Why would the path change? The DT should be stable.

It changes sometimes, such as
efb9adb27475 ("ARM: dts: imx6ul: Remove leading zeroes from unit addresses"),

in bootloader, we are using node path, so if the node name changes, the bootloader
will fail to disable the node.

Thanks,
Peng.

> 
> Rob