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From: Robin Murphy <robin.murphy@arm.com>
To: Bartosz Golaszewski <brgl@bgdev.pl>, Sekhar Nori <nsekhar@ti.com>,
	Kevin Hilman <khilman@kernel.org>,
	David Lechner <david@lechnology.com>,
	Michael Turquette <mturquette@baylibre.com>,
	Stephen Boyd <sboyd@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Rob Herring <robh+dt@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Yoshinori Sato <ysato@users.sourceforge.jp>,
	Rich Felker <dalias@libc.org>,
	Frank Rowand <frowand.list@gmail.com>,
	"Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
	Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
	Dmitry Torokhov <dmitry.torokhov@gmail.com>,
	Arend van Spriel <aspriel@gmail.com>,
	Heikki Krogerus <heikki.krogerus@linux.intel.com>,
	Michal Suchanek <msuchanek@suse.de>,
	Jan Kiszka <jan.kiszka@siemens.com>,
	Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	Bartosz Golaszewski <bgolaszewski@baylibre.com>
Subject: Re: [PATCH 00/11] platform: device tree support for early platform drivers
Date: Tue, 24 Apr 2018 19:19:14 +0100	[thread overview]
Message-ID: <9f097271-5953-9587-7dcb-a2a9368bd015@arm.com> (raw)
In-Reply-To: <20180424173051.15099-1-brgl@bgdev.pl>

On 24/04/18 18:30, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bgolaszewski@baylibre.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.
> 
> 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.

Eww, it's the "u-boot,dm-pre-reloc" mess all over again :(

The examples you give do represent hardware though - "syscon" falls wide 
of the DT abstraction of nice distinct devices, but is at least still 
describing a real relationship of some registers somewhere affecting 
some component somewhere else; GPIO hogs may not be real devices but 
they still describe a hardware configuration which the OS is expected to 
set up.

Things that describe pure consumer-specific software policy are a whole 
other level beyond that IMO.

> 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.

Admittedly it doesn't apply as super-early as timers and clocksources, 
but I feel compelled to point out that IOMMU_OF_DECLARE was already 
doing a variant on "early platform devices" for ages (until 4.16 when 
everything was finally cleaned up to rely on regular probe-deferral and 
left it as just a vestigial lookup table). AFAICS the same basic concept 
could translate to other subsystems without invasive DT changes.

Robin.

> Bartosz Golaszewski (11):
>    platform: early: provide early_platform_add_device()
>    platform: provide early_platform_driver_register_probe_all()
>    platform: make support for early platform devices conditional
>    of: platform: use pdev as name for vars of type struct platform_device
>    platform: use a dedicated list_head for early devices
>    of: provide for_each_compatible_child_node()
>    dt-bindings: add bindings for early devices
>    of: platform: provide of_early_platform_populate()
>    platform: provide early_platform_driver()
>    of: platform: provide of_early_platform_probe()
>    misc: implement a dummy early platform driver
> 
>   Documentation/devicetree/bindings/early.txt |   7 +
>   arch/sh/Kconfig                             |   1 +
>   drivers/base/Kconfig                        |   4 +
>   drivers/base/platform.c                     |  26 ++--
>   drivers/misc/Kconfig                        |   8 ++
>   drivers/misc/Makefile                       |   1 +
>   drivers/misc/dummy-early.c                  |  40 ++++++
>   drivers/of/device.c                         |  14 +-
>   drivers/of/platform.c                       | 143 +++++++++++++++-----
>   include/linux/device.h                      |   4 +
>   include/linux/of.h                          |   3 +
>   include/linux/of_device.h                   |   5 +
>   include/linux/of_platform.h                 |  19 +++
>   include/linux/platform_device.h             |  52 +++++++
>   14 files changed, 279 insertions(+), 48 deletions(-)
>   create mode 100644 Documentation/devicetree/bindings/early.txt
>   create mode 100644 drivers/misc/dummy-early.c
> 

  parent reply	other threads:[~2018-04-24 18:19 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-24 17:30 Bartosz Golaszewski
2018-04-24 17:30 ` [PATCH 01/11] platform: early: provide early_platform_add_device() Bartosz Golaszewski
2018-04-24 17:30 ` [PATCH 02/11] platform: provide early_platform_driver_register_probe_all() Bartosz Golaszewski
2018-04-24 17:30 ` [PATCH 03/11] platform: make support for early platform devices conditional Bartosz Golaszewski
2018-04-24 19:31   ` Randy Dunlap
2018-04-25 14:02   ` Rich Felker
2018-04-24 17:30 ` [PATCH 04/11] of: platform: use pdev as name for vars of type struct platform_device Bartosz Golaszewski
2018-04-24 17:30 ` [PATCH 05/11] platform: use a dedicated list_head for early devices Bartosz Golaszewski
2018-04-26  4:27   ` kbuild test robot
2018-04-24 17:30 ` [PATCH 06/11] of: provide for_each_compatible_child_node() Bartosz Golaszewski
2018-04-24 17:30 ` [PATCH 07/11] dt-bindings: add bindings for early devices Bartosz Golaszewski
2018-04-24 17:30 ` [PATCH 08/11] of: platform: provide of_early_platform_populate() Bartosz Golaszewski
2018-04-24 17:30 ` [PATCH 09/11] platform: provide early_platform_driver() Bartosz Golaszewski
2018-04-24 17:30 ` [PATCH 10/11] of: platform: provide of_early_platform_probe() Bartosz Golaszewski
2018-04-26  3:46   ` kbuild test robot
2018-04-24 17:30 ` [PATCH 11/11] misc: implement a dummy early platform driver Bartosz Golaszewski
2018-04-24 17:55 ` [PATCH 00/11] platform: device tree support for early platform drivers Mark Rutland
2018-04-24 17:59   ` Rich Felker
2018-04-24 17:57 ` Rich Felker
2018-04-25  9:33   ` Bartosz Golaszewski
2018-04-24 18:19 ` Robin Murphy [this message]
2018-04-24 19:39 ` Rob Herring

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