linux-kernel - Re: [PATCH v2 1/2] doc: bindings: Add bindings documentation for mtd nvmem

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Date:   Wed, 8 Mar 2017 17:25:04 +0100
From:   Boris Brezillon <boris.brezillon@...e-electrons.com>
To:     Alban <albeu@...e.fr>
Cc:     linux-kernel@...r.kernel.org, Mark Rutland <mark.rutland@....com>,
        Moritz Fischer <moritz.fischer@...us.com>,
        devicetree@...r.kernel.org, Richard Weinberger <richard@....at>,
        Marek Vasut <marek.vasut@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        linux-mtd@...ts.infradead.org,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Brian Norris <computersforpeace@...il.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Cyrille Pitchen <cyrille.pitchen@...el.com>
Subject: Re: [PATCH v2 1/2] doc: bindings: Add bindings documentation for
 mtd nvmem

Hi Alban,

On Wed, 8 Mar 2017 16:20:01 +0100
Alban <albeu@...e.fr> wrote:

> On Tue, 7 Mar 2017 22:01:07 +0100
> Boris Brezillon <boris.brezillon@...e-electrons.com> wrote:
> 
> > On Tue,  7 Mar 2017 09:26:03 +0100
> > Alban <albeu@...e.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@...e.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.

That was the plan.

> 
> > 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);
> 

Yep, works too. Let's wait for a DT review, before taking a decision.

Thanks,

Boris