lkml.org 
[lkml]   [2018]   [Apr]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH 00/11] platform: device tree support for early platform drivers
From
Date
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
>

\
 
 \ /
  Last update: 2018-04-24 20:19    [W:0.162 / U:0.916 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site