[PATCH v3 0/8] Driver core: Add faux bus devices

Greg Kroah-Hartman
2025-02-06T17:38:39Z

For years/decades now, I've been complaining when I see people use
platform devices for things that are obviously NOT platform devices.
To finally fix this up, here is a "faux bus" that should be used instead
of a platform device for these tiny and "fake" devices that people
create all over the place.

The api is even simpler than the normal platform device api, just two
functions, one to create a device and one to remove it. When a device
is created, if a probe/release callback is offered, they will be called
at the proper time in the device's lifecycle. When finished with the
device, just destroy it and all should be good.

This simple api should also hopefully provide for a simple rust binding
to it given the simple rules and lifecycle of the pointer passed back
from the creation function (i.e. it is alive and valid for as long as
you have not called destroy on it.)

I've also converted four different examples of platform device abuse, the
dummy regulator driver, the USB phy code, the x86 microcode dvice, and
the "regulator" device that wifi uses to load the firmware tables, to
use this api. In all cases, the logic either was identical, or became
simpler, than before, a good sign (side note, a bug was fixed in the usb
phy code that no one ever noticed before).

Note, unless there are major objections, I'm leaning toward getting
patch 1 of this series merged during this -rc cycle so that all of the
individual driver subsystem cleanups can go through those subsystems as
needed, as well as allowing the rust developers to create a binding and
get that merged easier. Having patch 1 merged on its own isn't going to
cause any changes if no one uses it, so that should be fine.

Changes from v3:
- Dropped the USB phy porting, turned out to be incorrect, it really
did need a platform device
- converted more drivers to the faux_device api (tlclk, lis3lv02d,
vgem, and vkms)
- collected some reviewed-by
- lots of minor tweaks of the faux.c api, and documentation based on
review, see the changelog in patch 1 for details.

Changes from v2:
- lots of cleanups to faux.c based on reviews, see patch 1 for details
- actually tested the destroy device path, it worked first try!
- added 3 more example drivers

Greg Kroah-Hartman (8):
driver core: add a faux bus for use when a simple device/bus is needed
regulator: dummy: convert to use the faux device interface
x86/microcode: move away from using a fake platform device
wifi: cfg80211: move away from using a fake platform device
tlclk: convert to use faux_device
misc: lis3lv02d: convert to use faux_device
drm/vgem/vgem_drv convert to use faux_device
drm/vkms: convert to use faux_device

Documentation/driver-api/infrastructure.rst | 6 +
arch/x86/kernel/cpu/microcode/core.c | 14 +-
drivers/base/Makefile | 2 +-
drivers/base/base.h | 1 +
drivers/base/faux.c | 228 ++++++++++++++++++++
drivers/base/init.c | 1 +
drivers/char/tlclk.c | 32 +--
drivers/gpu/drm/vgem/vgem_drv.c | 30 +--
drivers/gpu/drm/vkms/vkms_drv.c | 28 +--
drivers/gpu/drm/vkms/vkms_drv.h | 4 +-
drivers/misc/lis3lv02d/lis3lv02d.c | 26 +--
drivers/misc/lis3lv02d/lis3lv02d.h | 4 +-
drivers/regulator/dummy.c | 37 +---
include/linux/device/faux.h | 65 ++++++
net/wireless/reg.c | 28 +--
15 files changed, 383 insertions(+), 123 deletions(-)
create mode 100644 drivers/base/faux.c
create mode 100644 include/linux/device/faux.h

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2.48.1