linux-kernel - Re: [PATCH 11/13] nvmem: add support for cell lookups from machine code

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Date:   Wed, 5 Sep 2018 16:47:57 +0200
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Boris Brezillon <boris.brezillon@...tlin.com>
Cc:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Joachim Eastwood <manabian@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Jonathan Corbet <corbet@....net>, Sekhar Nori <nsekhar@...com>,
        Kevin Hilman <khilman@...nel.org>,
        David Lechner <david@...hnology.com>,
        Andrew Lunn <andrew@...n.ch>, Alban Bedel <albeu@...e.fr>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        linux-doc <linux-doc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [PATCH 11/13] nvmem: add support for cell lookups from machine code

2018-09-05 16:21 GMT+02:00 Boris Brezillon <boris.brezillon@...tlin.com>:
> On Wed, 5 Sep 2018 16:00:36 +0200
> Bartosz Golaszewski <brgl@...ev.pl> wrote:
>
>> 2018-09-05 15:57 GMT+02:00 Boris Brezillon <boris.brezillon@...tlin.com>:
>> > On Wed,  5 Sep 2018 11:57:36 +0200
>> > Bartosz Golaszewski <brgl@...ev.pl> wrote:
>> >
>> >>
>> >> +struct nvmem_cell_lookup {
>> >> +     const char              *nvmem_name;
>> >> +     const char              *dev_id;
>> >
>> > Shouldn't we have a con_id here?
>> >
>> >> +     const char              *cell_id;
>> >> +     struct list_head        node;
>> >> +};
>>
>> I wanted to stay in line with the current API - nvmem_cell_get() takes
>> as argument a string called cell_id. I wanted to reflect that here.
>
> Actually, you need both. con_id is the name you would have in your DT
> in the nvmem-cell-names property, cell_id is the name of the cell
> you'd find under the nvmem device node.
>
> Let's take an example:
>
>         mydev {
>                 #nvmem-cell-names = "mac-address", "revision";
>                 #nvmem-cells = <&cell1>, <&cell2>;
>         };
>
>         mynvmemdev {
>                 #size-cells = <1>;
>                 #address-cells = <1>;
>
>                 cell1: foo@0 {
>                         reg = <0x0 0x6>;
>                 };
>
>                 cell2: bar@6 {
>                         reg = <0x6 0x10>;
>                 };
>         };
>
> this can be described the same way using a consumer lookup table:
>
> struct nvmem_cell_lookup_entry {
>         const char *con_id;
>         const char *nvmem_name;
>         const char *cell_name;
> };
>
> struct nvmem_cell_lookup_table {
>         struct list_head node;
>         const char *dev_id;
>         unsigned int nentries;
>         const struct nvmem_cell_lookup_entry *entries;
> }
>
> static const struct nvmem_cell_lookup_entry mydev_nvmem_cells[] = {
>         {
>                 .con_id = "mac-address",
>                 .nvmem_name = "mynvmemdev",
>                 .cell_name = "foo",
>         },
>         {
>                 .con_id = "revision",
>                 .nvmem_name = "mynvmemdev",
>                 .cell_name = "bar",
>         },
> }
>
> static const struct nvmem_cell_lookup_table mydev_nvmem_lookup = {
>         .dev_id = "mydev.0",
>         .nentries = ARRAY_SIZE(mydev_nvmem_cells),
>         .entries = mydev_nvmem_cells,
> };
>
>
> ...
>
>         nvmem_add_cell_lookups(&mydev_nvmem_lookup);

Ok I get it. Shouldn't we change the argument name of nvmem_cell_get()
and friends from 'name' to 'con_id' or simply 'id' similarly to what
other frameworks do to avoid such confusion?

I also don't see a need for splitting the lookup into two structures
here. Something like:

struct nvmem_cell_lookup {
        const char *nvmem_name;
        const char *cell_name;
        const char *dev_id;
        const char *con_id;
};

Would be perfectly fine and would allow to register all lookups for
given machine with a single call. How often does it happen that a
single device needs multiple nvmem cells anyway?

Bart