Re: [PATCH v2 06/29] mtd: Add support for reading MTD devices via the nvmem API

Boris Brezillon
2018-08-21T10:43:52Z

On Tue, 21 Aug 2018 11:11:58 +0100
Srinivas Kandagatla <srinivas.kandagatla@linaro.org> wrote:

> On 21/08/18 10:56, Boris Brezillon wrote:
> > On Tue, 21 Aug 2018 10:50:07 +0100
> > Srinivas Kandagatla<srinivas.kandagatla@linaro.org> wrote:
> >
> >> On 20/08/18 19:20, Boris Brezillon wrote:
> >>> On Mon, 20 Aug 2018 11:43:34 +0100
> >>> Srinivas Kandagatla<srinivas.kandagatla@linaro.org> wrote:
> >>>
> >>>> Overall am still not able to clear visualize on how MTD bindings with
> >>>> nvmem cells would look in both partition and un-partition usecases?
> >>>> An example DT would be nice here!!
> >>> Something along those lines:
> >>>
> >> This looks good to me.
> >>> mtdnode {
> >>> nvmem-cells {
> >>> #address-cells = <1>;
> >>> #size-cells = <1>;
> >>>
> >>> cell@0 {
> >>> reg = <0x0 0x14>;
> >>> };
> >>> };
> >>>
> >>> partitions {
> >>> compatible = "fixed-partitions";
> >>> #address-cells = <1>;
> >>> #size-cells = <1>;
> >>>
> >>> partition@0 {
> >>> reg = <0x0 0x20000>;
> >>>
> >>> nvmem-cells {
> >>> #address-cells = <1>;
> >>> #size-cells = <1>;
> >>>
> >>> cell@0 {
> >>> reg = <0x0 0x10>;
> >>> };
> >>> };
> >>> };
> >>> };
> >>> }; >
> >> Just curious...Is there a reason why we can't do it like this?:
> >> Is this because of issue of #address-cells and #size-cells Or mtd
> >> bindings always prefer subnodes?
> >>
> >> mtdnode {
> >> reg = <0x0123000 0x40000>;
> >> #address-cells = <1>;
> >> #size-cells = <1>;
> >> cell@0 {
> >> compatible = "nvmem-cell";
> >> reg = <0x0 0x14>;
> >> };
> >>
> >> partitions {
> >> compatible = "fixed-partitions";
> >> #address-cells = <1>;
> >> #size-cells = <1>;
> >>
> >> partition@0 {
> >> reg = <0x0 0x20000>;
> >> cell@0 {
> >> compatible = "nvmem-cell";
> >> reg = <0x0 0x10>;
> >> };
> >> };
> >> };
> >> };
> > It's because partitions were initially directly defined under the mtd
> > node, so, if you have an old DT you might have something like:
> >
> > mtdnode {
> > reg = <0x0123000 0x40000>;
> > #address-cells = <1>;
> > #size-cells = <1>;
> >
> > partition@0 {
> > reg = <0x0 0x20000>;
> > ...
> > };
> > ...
> > };
> >
> > If we use such a DT with this patch applied, the NVMEM framework will
> > consider MTD partitions as nvmem cells, which is not what we want.
> Yep, I agree.
> TBH, I wanted to add compatible string to nvmem-cell at some point in
> time and it seems more natural update too. One of the reason we
> discussed this in the past was parsers. Looks like mtd can make use of this.
>
> We should be able to add this as an optional flag in nvmem_config to
> enforce this check in case providers wanted to.
>
> Do you think that would help mtd nvmem case?

Yes, it should work if nvmem cells are defined directly under the mtd
node (or the partition they belong to).

> Also I felt like nvmem-cells subnode seems to be a bit heavy!

I still think grouping nvmem cells in a subnode is cleaner (just like
we do for partitions), but I won't object if all parties (you, Alban
and Rob) agree on this solution.