netdev - RE: [PATCH 0/4] dt-bindings: imx: add nvmem property

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Message-ID: <DU0PR04MB941779F67C9FFE6BD4334B6188199@DU0PR04MB9417.eurprd04.prod.outlook.com>
Date:   Thu, 24 Mar 2022 12:21:30 +0000
From:   Peng Fan <peng.fan@....com>
To:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        "Peng Fan (OSS)" <peng.fan@....nxp.com>
CC:     "ulf.hansson@...aro.org" <ulf.hansson@...aro.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "krzk+dt@...nel.org" <krzk+dt@...nel.org>,
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        Joakim Zhang <qiangqing.zhang@....com>,
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        <linux-arm-kernel@...ts.infradead.org>,
        "srinivas.kandagatla@...aro.org" <srinivas.kandagatla@...aro.org>
Subject: RE: [PATCH 0/4] dt-bindings: imx: add nvmem property

> Subject: Re: [PATCH 0/4] dt-bindings: imx: add nvmem property
> 
> Hello,
> 
> On Thu, Mar 24, 2022 at 12:20:20PM +0800, Peng Fan (OSS) wrote:
> > From: Peng Fan <peng.fan@....com>
> >
> > To i.MX SoC, there are many variants, such as i.MX8M Plus which
> > feature 4 A53, GPU, VPU, SDHC, FLEXCAN, FEC, eQOS and etc.
> > But i.MX8M Plus has many parts, one part may not have FLEXCAN, the
> > other part may not have eQOS or GPU.
> > But we use one device tree to support i.MX8MP including its parts,
> > then we need update device tree to mark the disabled IP status "disabled".
> >
> > In NXP U-Boot, we hardcoded node path and runtime update device tree
> > status in U-Boot according to fuse value. But this method is not
> > scalable and need encoding all the node paths that needs check.
> >
> > By introducing nvmem property for each node that needs runtime update
> > status property accoridng fuse value, we could use one Bootloader code
> > piece to support all i.MX SoCs.
> >
> > The drawback is we need nvmem property for all the nodes which maybe
> > fused out.
> 
> I'd rather not have that in an official binding as the syntax is orthogonal to
> status = "..." but the semantic isn't. Also if we want something like that, I'd
> rather not want to adapt all bindings, but would like to see this being generic
> enough to be described in a single catch-all binding.
> 
> I also wonder if it would be nicer to abstract that as something like:
> 
> 	/ {
> 		fuse-info {
> 			compatible = "otp-fuse-info";
> 
> 			flexcan {
> 				devices = <&flexcan1>, <&flexcan2>;
> 				nvmem-cells = <&flexcan_disabled>;
> 				nvmem-cell-names = "disabled";
> 			};
> 
> 			m7 {
> 				....
> 			};
> 		};
> 	};
> 
> as then the driver evaluating this wouldn't need to iterate over the whole dtb
> but just over this node. But I'd still keep this private to the bootloader and not
> describe it in the generic binding.

Good idea. But I still prefer Linux accept this binding and related device tree as
you described above, because U-Boot sync with linux device tree and bindings.

Thanks,
Peng.

> 
> Just my 0.02€
> Uwe