linux-kernel - Re: [PATCH RFC PoC 0/2] platform: different approach to early platform drivers

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Date:   Fri, 27 Apr 2018 10:59:15 +0200
From:   Bartosz Golaszewski <bgolaszewski@...libre.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Sekhar Nori <nsekhar@...com>, David Lechner <david@...hnology.com>,
        Rich Felker <dalias@...c.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Kevin Hilman <khilman@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Frank Rowand <frowand.list@...il.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Arend van Spriel <aspriel@...il.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Michal Suchanek <msuchanek@...e.de>,
        Jan Kiszka <jan.kiszka@...mens.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Marc Zyngier <marc.zyngier@....com>,
        Peter Rosin <peda@...ntia.se>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>
Subject: Re: [PATCH RFC PoC 0/2] platform: different approach to early
 platform drivers

2018-04-27 10:55 GMT+02:00 Arnd Bergmann <arnd@...db.de>:
> On Fri, Apr 27, 2018 at 10:29 AM, Sekhar Nori <nsekhar@...com> wrote:
>> On Friday 27 April 2018 01:22 PM, Arnd Bergmann wrote:
>>> On Fri, Apr 27, 2018 at 4:28 AM, David Lechner <david@...hnology.com> wrote:
>>>> On 04/26/2018 12:31 PM, Rich Felker wrote:
>
>>>
>>> I haven't seen the discussion about your clock drivers, but I know that
>>> usually only a very small subset of the clocks on an SoC are needed
>>> that 'early', and you should use a regular platform driver for the rest.
>>
>> Its true that the subset is small, but they are either PLL bypass clocks
>> or clocks derived out of the main clock gate controller on the Soc
>> (DaVinci PSC). So we need some non-platform-device based initialization
>> support in the two main clock drivers used on mach-davinci anyway.
>>
>>> Can you elaborate on which devices need to access your clocks before
>>> you are able to initialize the clk driver through the regular platform_driver
>>> framework? Do any of these need complex interactions with the clk
>>> subsystem, or do you just need to ensure they are turned on?
>>
>> Its just the timer IP. There is no complex interaction, just need to
>> ensure that the clock is registered with the framework and also switched
>> on when there is a gate clock.
>>
>> The latest attempt by David for this was posted last night here:
>>
>> https://lkml.org/lkml/2018/4/26/1093
>
> Ok, so the workaround in that series is to set up the timer clk manually
> in the SoC specific code (dm365_init_time etc) and register it to the
> clk subsystem, right?
>
> That seems to be a much more appropriate workaround than adding
> back early_platform devices. We can always try to do something better
> later, but for now I'm happy with that as a workaround.
>

Just to clarify: this is not bringing back the hacky early platform
devices from before. It's a new approach that actually uses the linux
platform driver model (unlike the current mechanism which only uses
the same data structures).

Thanks,
Bart