Messages in this thread | | | Subject | Re: [PATCH 00/11] platform: device tree support for early platform drivers | From | Robin Murphy <> | Date | Tue, 24 Apr 2018 19:19:14 +0100 |
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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 >
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