On Tue, 7 Mar 2017 22:01:07 +0100
Boris Brezillon <boris.brezillon@free-electrons.com> wrote:

> On Tue,  7 Mar 2017 09:26:03 +0100
> Alban <albeu@free.fr> wrote:
> 
> > Config data for drivers, like MAC addresses, is often stored in MTD.
> > Add a binding that define how such data storage can be represented in
> > device tree.
> > 
> > Signed-off-by: Alban <albeu@free.fr>
> > ---
> > Changelog:
> > v2: * Added a "Required properties" section with the nvmem-provider
> >       property
> > ---
> >  .../devicetree/bindings/nvmem/mtd-nvmem.txt        | 33 ++++++++++++++++++++++
> >  1 file changed, 33 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/nvmem/mtd-nvmem.txt
> > 
> > diff --git a/Documentation/devicetree/bindings/nvmem/mtd-nvmem.txt b/Documentation/devicetree/bindings/nvmem/mtd-nvmem.txt
> > new file mode 100644
> > index 0000000..8ed25e6
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/nvmem/mtd-nvmem.txt
> > @@ -0,0 +1,33 @@
> > += NVMEM in MTD =
> > +
> > +Config data for drivers, like MAC addresses, is often stored in MTD.
> > +This binding define how such data storage can be represented in device tree.
> > +
> > +An MTD can be defined as an NVMEM provider by adding the `nvmem-provider`
> > +property to their node.  
> 
> If everyone agrees that this is actually needed, then it should
> definitely go in the nvmem binding doc, and we should patch all nvmem
> providers to define this property (even if we keep supporting nodes
> that are not defining it). I'm not fully convinced yet, but I might be
> wrong.

I really like to hear what the DT people think about this.

> I also think we should take the "nvmem under flash node without partitions"
> into account now, or at least have a clear plan on how we want to represent
> it.
> 
> Something like that?

Yes, but with the following extras:

> 	flash {
                nvmem-provider;
> 		partitions {
> 			part@X {
> 				nvmem {
  					compatible = "nvmem-cells";
> 					#address-cells = <1>;
> 					#size-cells = <1>;
> 
> 					cell@Y {
> 					};
> 				};
> 			};
> 		};
> 
> 		nvmem {
  			compatible = "nvmem-cells";
> 			#address-cells = <1>;
> 			#size-cells = <1>;
> 
> 			cell@X {
> 			};
> 		};
> 	};
>
> Note that patching nvmem core to support the subnode case should be
> pretty easy (see below).

This shouldn't be needed as nothing would change for the NVMEM devices,
what could be added is a check for the "nvmem-provider" property.
To support the proposed binding we would only need a minor change to
of_nvmem_cell_get():

diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
index 408b521ee520..6231ea27c9f4 100644
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -444,6 +444,10 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
        if (!config->dev)
                return ERR_PTR(-EINVAL);

+       if (config->dev->of_node &&
+           !of_property_read_bool(config->dev->of_node, "nvmem-provider"))
+               return ERR_PTR(-ENODEV);
+
        nvmem = kzalloc(sizeof(*nvmem), GFP_KERNEL);
        if (!nvmem)
                return ERR_PTR(-ENOMEM);
@@ -777,6 +781,15 @@ struct nvmem_cell *of_nvmem_cell_get(struct device_node *np,
        if (!nvmem_np)
                return ERR_PTR(-EINVAL);

+       /* handle the new cell binding */
+       if (of_device_is_compatible(nvmem_np, "nvmem-cells")) {
+               nvmem_np = of_get_next_parent(cell_np);
+               if (!nvmem_np)
+                       return ERR_PTR(-EINVAL);
+               if (!of_property_read_bool(nvmem_np, "nvmem-provider"))
+                       return ERR_PTR(-ENODEV);
+       }
+
        nvmem = __nvmem_device_get(nvmem_np, NULL, NULL);
        if (IS_ERR(nvmem))
                return ERR_CAST(nvmem);


> --->8---  
> diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
> index 408b521ee520..507c6190505b 100644
> --- a/drivers/nvmem/core.c
> +++ b/drivers/nvmem/core.c
> @@ -465,7 +465,7 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
>         nvmem->priv = config->priv;
>         nvmem->reg_read = config->reg_read;
>         nvmem->reg_write = config->reg_write;
> -       np = config->dev->of_node;
> +       np = config->of_node ? : config->dev->of_node;
>         nvmem->dev.of_node = np;
>         dev_set_name(&nvmem->dev, "%s%d",
>                      config->name ? : "nvmem", config->id);
> diff --git a/include/linux/nvmem-provider.h b/include/linux/nvmem-provider.h
> index cd93416d762e..ec2f5116d62d 100644
> --- a/include/linux/nvmem-provider.h
> +++ b/include/linux/nvmem-provider.h
> @@ -21,6 +21,7 @@ typedef int (*nvmem_reg_write_t)(void *priv, unsigned int offset,
>  
>  struct nvmem_config {
>         struct device           *dev;
> +       struct device_node      *of_node;
>         const char              *name;
>         int                     id;
>         struct module           *owner;