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