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

[Peng Fan]

> Subject: Re: [RFC 1/2] dt-bindings: imx-ocotp: Add fusable-node property
> 
> On 20.05.2019 06:06, 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@xxxxxxx>
> > ---
> >
> > Currently NXP vendor use U-Boot to set status to disabled for devices
> > that could not function,
> >
> https://source.codeaurora.org/external/imx/uboot-imx/tree/arch/arm/mac
> > h-imx/mx6/module_fuse.c?h=imx_v2018.03_4.14.98_2.0.0_ga#n149
> > But this approach is will not work if kernel dts node path changed.
> >
> > There are two approaches to resolve:
> >
> > 1. This patch is to add a fusable-node property, and Firmware will parse
> >     the property and read fuse to decide whether to disable or keeep
> enable
> >     the nodes.
> >
> > 2. There is another approach is that add nvmem-cells for all nodes that
> >     could be disabled(fused). Then in each linux driver to use nvmem
> >     api to detect fused or not, or in linux driver common code to check
> >     device functionable or not with nvmem API.
> >
> >
> > To make it easy to work, we choose [1] here. Please advise whether it
> > is acceptable, because the property is not used by linux driver in
> > approach [1]. Or you prefer [2] or please advise if any better solution.
> 
> Couldn't firmware parse nvmem-cells? Even without a full nvmem subsystem
> it would be possible for imx-specific code to walk the entire device tree, parse
> nvmem-cells and disable nodes which are disabled by fuse.

Firmware could parse nvmem-cells, but there are lots of modules that could
be fused. If using nvmem-cells, that means need to add nvmem property
for all the modules that could be fused. To make is looks cleaner, so introduced
a fusable-node property.

Regards,
Peng.

> 
> --
> Regards,
> Leonard