linux-kernel - Re: [PATCH 00/11] platform: device tree support for early platform drivers

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Date:   Wed, 25 Apr 2018 11:33:42 +0200
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Rich Felker <dalias@...c.org>
Cc:     Sekhar Nori <nsekhar@...com>, Kevin Hilman <khilman@...nel.org>,
        David Lechner <david@...hnology.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        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>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [PATCH 00/11] platform: device tree support for early platform drivers

2018-04-24 19:57 GMT+02:00 Rich Felker <dalias@...c.org>:
> On Tue, Apr 24, 2018 at 07:30:40PM +0200, Bartosz Golaszewski wrote:
>> From: Bartosz Golaszewski <bgolaszewski@...libre.com>
>>
>> Device tree based systems often use OF_DECLARE() macros for devices
>> that need to be initialized early in the boot process such as clocks,
>> timers etc. However platform devices are more desirable.
>>
>> This series aims at introducing support for early platform drivers for
>> OF-based systems.
>>
>> The idea is to have a special compatible fallback string: "earlydev"
>> that similarily to "syscon" would be added to device nodes that need
>> early probing. We then need to call of_early_platform_populate() early
>> in the boot process to actually probe the registered devices.
>
> This makes no sense to me. It's not the device tree that should
> contain the knowledge that these need to be registered/probed early in
> the boot. That need is a property of the operating system/device
> drivers, and so the *drivers* should be the ones that contain the
> knowledge.
>
>> I am aware that this new compatible does not strictly correspond with
>> the "hardware description only" rule of DT, but we already have many
>> functionalities that break this rule: syscon, gpio hogs etc.
>>
>> The first user of this new functionality will be the DaVinci platform
>> for which we want to probe the pll, psc and timer drivers early in the
>> boot sequence but keep them implemented as platform drivers.
>>
>> In the future, if this series gets accepted, this could become and
>> alternative to TIMER_OF_DECLARE, CLK_OF_DECLARE etc. and could lead
>> to deprecating of those macros in favor of early platform drivers.
>
> This seems completely unacceptable, in that it would render new
> kernels unable to boot on existing device trees (which may be
> hard-coded in rom on existing devices).
>

Just ot make it clear: by deprecating I meant not accepting any new
users, not blindly replacing the current ones.

Thanks,
Bart