lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  PHC 
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:   Fri, 27 Apr 2018 09:52:51 +0200
From:   Arnd Bergmann <>
To:     David Lechner <>
Cc:     Rich Felker <>, Bartosz Golaszewski <>,
        Sekhar Nori <>,
        Kevin Hilman <>,
        Michael Turquette <>,
        Stephen Boyd <>,
        Greg Kroah-Hartman <>,
        Rob Herring <>,
        Mark Rutland <>,
        Yoshinori Sato <>,
        Frank Rowand <>,
        "Rafael J . Wysocki" <>,
        Jarkko Sakkinen <>,
        Dmitry Torokhov <>,
        Arend van Spriel <>,
        Heikki Krogerus <>,
        Michal Suchanek <>,
        Jan Kiszka <>,
        Andy Shevchenko <>,
        Marc Zyngier <>,
        Peter Rosin <>,
        Linux ARM <>,
        Linux Kernel Mailing List <>,
        DTML <>,
        Bartosz Golaszewski <>
Subject: Re: [PATCH RFC PoC 0/2] platform: different approach to early
 platform drivers

On Fri, Apr 27, 2018 at 4:28 AM, 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 <>
>>> 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.

The early_platform code is certainly not a way to make things simpler,
it just adds one more way of doing the same thing that OF_CLK_DECLARE
already does. We removed the last early_platform users on ARM a few
years ago, and I would hope to leave it like that.

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.

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?


Powered by blists - more mailing lists