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

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Date:   Thu, 26 Apr 2018 22:54:21 -0400
From:   Rich Felker <dalias@...c.org>
To:     David Lechner <david@...hnology.com>
Cc:     Bartosz Golaszewski <brgl@...ev.pl>, Sekhar Nori <nsekhar@...com>,
        Kevin Hilman <khilman@...nel.org>,
        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>,
        Marc Zyngier <marc.zyngier@....com>,
        Peter Rosin <peda@...ntia.se>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [PATCH RFC PoC 0/2] platform: different approach to early
 platform drivers

On Thu, Apr 26, 2018 at 09:28:39PM -0500, David Lechner wrote:
> On 04/26/2018 12:31 PM, Rich Felker wrote:
> >On Thu, Apr 26, 2018 at 05:29:18PM +0200, Bartosz Golaszewski wrote:
> >>From: Bartosz Golaszewski <bgolaszewski@...libre.com>
> >>
> >>This is a follow to my series[1] the aim of which was to introduce device tree
> >>support for early platform devices.
> >>
> >>It was received rather negatively. Aside from using device tree to pass
> >>implementation specific details to the system, two important concerns were
> >>raised: no probe deferral support and the fact that currently the early devices
> >>never get converted to actual platform drivers. This series is a
> >>proof-of-concept that's trying to address those issues.
> >>
> >>The only user of the current version of early platform drivers is the SuperH
> >>architecture. If this series eventually gets merged, we could simply replace
> >>the other solution.
> >
> >Looking at a quick output of:
> >
> >	grep -r -A10 early_devices[[] arch/sh/kernel/
> >
> >it looks like all of the existing early platform devices are serial
> >ports, clocks, and clocksources. The switch to device tree should pick
> >them all up from CLK_OF_DECLARE, TIMER_OF_DECLARE, and
> >EARLYCON_DECLARE. Until that's complete, the existing code works
> >as-is. I don't see what problem you're trying to solve.
> 
> The problem for us is that clk maintainers don't want new drivers to use
> CLK_OF_DECLARE and instead use platform devices. I have just written such
> a new driver that is shared by 6 different SoCs. For some combinations of
> SoCs and clocks, using a platform device is fine but on others we need to
> register early, so the drivers now have to handle both cases, which is
> kind of messy and fragile. If there is a generic way to register platform
> devices early, then the code is simplified because we only have to handle
> one method of registering the clocks instead of two.

Can you get them to explain why? This sounds wrong.

Rich