pt., 11 maj 2018 o 18:21 Bartosz Golaszewski <brgl@xxxxxxxx> napisał(a): > > This series is a follow-up to the RFC[1] posted a couple days ago. > > NOTE: this series applies on top of my recent patches[2] that move the previous > implementation of early platform devices to arch/sh. > > Problem: > > Certain class of devices, such as timers, certain clock drivers and irq chip > drivers need to be probed early in the boot sequence. The currently preferred > approach is using one of the OF_DECLARE() macros. This however does not create > a platform device which has many drawbacks - such as not being able to use > devres routines, dev_ log functions or no way of deferring the init OF function > if some other resources are missing. > > For drivers that use both platform drivers and OF_DECLARE the situation is even > more complicated as the code needs to take into account that there can possibly > be no struct device present. For a specific use case that we're having problems > with, please refer to the recent DaVinci common-clock conversion patches and > the nasty workaround that this problem implies[3]. > > We also used to have an early platform drivers implementation but they were not > integrated with the linux device model at all - they merely used the same data > structures. The users could not use devres, defer probe and the early devices > never became actual platform devices later on. > > Proposed solution: > > This series aims at solving this problem by (re-)introducing the concept of > early platform drivers and devices - this time however in a way that seamlessly > integrates with the existing platform drivers and also offers device-tree > support. > > The idea is to provide a way for users to probe devices early, while already > being able to use devres, devices resources and properties and also deferred > probing. > > New structures are introduced: the early platform driver contains the > early_probe callback which has the same signature as regular platform_device > probe. This callback is called early on. The user can have both the early and > regular probe speficied or only one of them and they both receive the same > platform device object as argument. Any device data allocated early will be > carried over to the normal probe. > > The architecture code is responsible for calling early_platform_start() in > which the early drivers will be registered and devices populated from DT. > > Once the device and kobject mechanisms are ready, all early drivers and devices > will be converted into real platform drivers and devices. Also: if any of the > early platform registration functions will be called once early initialization > is done, these functions will work like regular platform_device/driver ones. > > Patches 1-9/12 introduce changes to existing code that are necessary before > adding support for early drivers. Patch 10/12 contains the new framwork in an > isolated file which can be compiled only if needed by the architecture. > > Patch 11/12 contains a dummy early platform driver that serves as a code > example and can be used for simple testing. > > The last patch finally makes the of/platform code aware of early platform > drivers. > > If accepted, this new mechanism could potentially lead to consolidation of the > code currently used by users of OF_DECLARE, since they could be converted to > actual platform drivers. > > [1] https://lkml.org/lkml/2018/4/26/657 > [2] https://lkml.org/lkml/2018/4/30/547 > [3] https://lkml.org/lkml/2018/4/26/1094 > > Bartosz Golaszewski (12): > platform/early: add a new field to struct device > platform/early: don't WARN() on non-empty devres list for early > devices > platform/early: export platform_match() locally > platform: provide a separate function for initializing platform > devices > platform: export platform_device_release() locally > of: add a new flag for OF device nodes > of/platform: provide a separate routine for setting up device > resources > of/platform: provide a separate routine for device initialization > platform/early: add an init section for early driver data > platform/early: implement support for early platform drivers > misc: implement a dummy early platform driver > of/platform: make the OF code aware of early platform drivers > > drivers/base/Kconfig | 3 + > drivers/base/Makefile | 1 + > drivers/base/base.h | 4 + > drivers/base/dd.c | 2 +- > drivers/base/early.c | 332 ++++++++++++++++++++++++++++++ > drivers/base/platform.c | 28 ++- > drivers/misc/Kconfig | 8 + > drivers/misc/Makefile | 2 + > drivers/misc/dummy-early.c | 82 ++++++++ > drivers/of/platform.c | 85 +++++--- > include/asm-generic/vmlinux.lds.h | 11 + > include/linux/device.h | 1 + > include/linux/early_platform.h | 75 +++++++ > include/linux/of.h | 1 + > include/linux/of_platform.h | 2 + > include/linux/platform_device.h | 2 + > 16 files changed, 604 insertions(+), 35 deletions(-) > create mode 100644 drivers/base/early.c > create mode 100644 drivers/misc/dummy-early.c > create mode 100644 include/linux/early_platform.h > > -- > 2.17.0 > Hi For anyone interested: I'll be doing a BoF about early platform drivers next week on Monday at 6:00pm during the ELCE 2018 in Edinburgh. It would be great to discuss this topic personally. Best regards and hope to see you there Bartosz Golaszewski
