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

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Date:   Mon, 22 Jan 2018 17:09:47 +0530
From:   Sekhar Nori <nsekhar@...com>
To:     Arnd Bergmann <arnd@...db.de>
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 Monday 22 January 2018 04:38 PM, Arnd Bergmann wrote:
> 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;

I think this works as well and does not need any new API. For clocks,
there is no platform data AFAICT, so it will have to be whatever
structure is being used to pass clock info to CCF driver (like perhaps
an addition parameter to da850_pll_clk_init() in David's under-review
DaVinci CCF conversion series).

> 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.

Yeah, I just noticed that too. syscon_regmap_lookup_by_pdevname has only
two callers in kernel. The call from clps711x.c UART driver does not
seem to be needed anymore after clps711x was converted to DT-only in v4.8

The other user is phy-da8xx-usb.c which this series is trying to get rid
of. So, perhaps syscon_regmap_lookup_by_pdevname() should be dropped by
v2 of this series.

Thanks,
Sekhar