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SubjectRe: [PATCH 00/12] introduce support for early platform drivers
pt., 11 maj 2018 o 18:21 Bartosz Golaszewski <brgl@bgdev.pl> 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

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