On-demand device registration

Hi,

while reading the thread [0] that Alexander Holler started with his series
to make probing order deterministic, it occurred to me that it should be
possible to achieve the same by probing devices as they are referenced by
other devices. 

This basically reuses the information that is already embedded in the
probe() implementations, saving us from refactoring existing drivers or
adding information to DTBs. 

The main issue I see is that the registration code path in some subsystems
may not be reentrant, so some refactoring of the locking will be needed. In
my testing I have found this problem with regulators, as the supply of a
regulator might end up being registered during the registration of the
first one. 

Something I'm not completely happy with is that I have had to move the
population of the device tree after all platform drivers have been
registered. Otherwise I don't see how I could register drivers on demand as
we don't have yet each driver's compatible strings. 

I have done my testing on a Tegra124-based Chromebook, and these patches
were enough to eliminate all the deferred probes. 

Regards,

Tomeu

[0] https://lkml.org/lkml/2014/5/12/452

Tomeu Vizoso (12):
  ARM: tegra: Register drivers before devices
  ARM: tegra: Add gpio-ranges property
  of/platform: add of_platform_device_ensure()
  gpio: Probe GPIO drivers on demand
  gpio: Probe pinctrl devices on demand
  regulator: core: Probe regulators on demand
  drm: Probe panels on demand
  drm/tegra: Probe dpaux devices on demand
  i2c: core: Probe i2c master devices on demand
  pwm: Probe PWM chip devices on demand
  backlight: Probe backlight devices on demand
  usb: phy: Probe phy devices on demand

 arch/arm/boot/dts/tegra124.dtsi     |  1 +
 arch/arm/mach-tegra/tegra.c         | 21 ++++++++-------------
 drivers/gpio/gpiolib-of.c           |  5 +++++
 drivers/gpu/drm/drm_panel.c         |  3 +++
 drivers/gpu/drm/tegra/dpaux.c       |  3 +++
 drivers/i2c/i2c-core.c              |  3 +++
 drivers/of/platform.c               | 28 ++++++++++++++++++++++++++++
 drivers/pwm/core.c                  |  3 +++
 drivers/regulator/core.c            |  2 ++
 drivers/usb/phy/phy.c               |  3 +++
 drivers/video/backlight/backlight.c |  3 +++
 include/linux/of_platform.h         |  2 ++
 12 files changed, 64 insertions(+), 13 deletions(-)

-- 
2.3.6

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