linux-kernel - Re: [PATCH 1/6] mfd: syscon: Add syscon

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Date:   Mon, 22 Jan 2018 12:08:59 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Sekhar Nori <nsekhar@...com>
Cc:     David Lechner <david@...hnology.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Kevin Hilman <khilman@...nel.org>,
        Lee Jones <lee.jones@...aro.org>,
        Kishon Vijay Abraham I <kishon@...com>,
        Adam Ford <aford173@...il.com>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/6] mfd: syscon: Add syscon_register() function

On Mon, Jan 22, 2018 at 11:53 AM, Sekhar Nori <nsekhar@...com> wrote:
> On Saturday 20 January 2018 08:50 AM, David Lechner wrote:
>> This adds a new syscon_register() function that creates a new syscon
>> regmap and adds it to the lookup list.
>
> /*
>  * registers a "global" syscon "device", usually not backed by a real
>  * device. To be used only in cases where the syscon is not
>  * related to any actual device, like system clocks, for example.
>  *
>  * name passed here must be globally unique.
>  */
> struct regmap *syscon_register_by_name(resource_size_t start, size_t
>                                        size, const char *name);
>
> and
>
> struct regmap *syscon_regmap_lookup_by_name(const char *name);
>
> I understand, with this the driver becomes little more complicated and
> DT and non-DT cases still need to be handled differently. But I think
> thats not the main issue you are trying to solve.

I think the easiest way to handle this in traditional board files is to use
a platform_data structure: when the platform registers the syscon,
it holds a pointer to the regmap and can simply add pass it to any
device using the syscon through platform_data. The driver using it
then does:

if (dev->of_node) {
      priv->regmap = syscon_regmap_lookup_by_phandle(...);
else
      priv->regmap = pdata->regmap;

At some point, we had a syscon_regmap_lookup_by_pdevname()
that was introduced for a similar case, but we should just kill that
now, after the platform that needed it is DT-only.

       Arnd