Re: [PATCH 00/21] On-demand device registration

On Mon, May 25, 2015 at 9:53 AM, Tomeu Vizoso
[off-list ref] wrote:

Hello,

I have a problem with the panel on my Tegra Chromebook taking longer than
expected to be ready during boot (Stéphane Marchesin reported what is
basically the same issue in [0]), and have looked into ordered probing as a
better way of solving this than moving nodes around in the DT or playing with
initcall levels.

While reading the thread [1] 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 registering devices as they are referenced by other
devices.

I like the concept and novel approach.

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

Something I'm not completely happy with is that I have had to move the call to
of_platform_populate 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.

Yeah, this is the opposite of what we'd really like. Ideally, we would
have a solution that works for modules too. However, we're no worse
off. We pretty much build-in dependencies to avoid module ordering
problems.

Perhaps we need to make the probing on-demand rather than simply on
device<->driver match occurring.

For machs that don't move of_platform_populate() to a later point, these
patches shouldn't cause any problems but it's not guaranteed that we'll avoid
all the deferred probes as some drivers may not be registered yet.

Ideally, of_platform_populate is not explicitly called by each
platform. So I think we need to make this work for the default case.

I have tested this on boards with Tegra, iMX.6 and Exynos SoCs, and these
patches were enough to eliminate all the deferred probes.

With this series I get the kernel to output to the panel in 0.5s, instead of 2.8s.

That's certainly compelling.

Rob

Regards,

Tomeu

[0] http://lists.freedesktop.org/archives/dri-devel/2014-August/066527.html

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

Tomeu Vizoso (21):
  regulator: core: Reduce critical area in _regulator_get
  ARM: tegra: Add gpio-ranges property
  ARM: tegra: Register drivers before devices
  ARM: EXYNOS: Register drivers before devices
  ARM i.MX6q: Register drivers before devices
  of/platform: Add of_platform_device_ensure()
  of/platform: Ensure device registration on lookup
  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
  clk: Probe clk providers on demand
  pinctrl: Probe pinctrl devices on demand
  phy: core: Probe phy providers on demand
  dma: of: Probe DMA controllers on demand
  power-supply: Probe power supplies on demand

 arch/arm/boot/dts/tegra124.dtsi     |  1 +
 arch/arm/mach-exynos/exynos.c       |  4 +--
 arch/arm/mach-imx/mach-imx6q.c      | 12 ++++-----
 arch/arm/mach-tegra/tegra.c         | 21 ++++++---------
 drivers/clk/clk.c                   |  3 +++
 drivers/dma/of-dma.c                |  3 +++
 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               | 53 +++++++++++++++++++++++++++++++++++++
 drivers/phy/phy-core.c              |  3 +++
 drivers/pinctrl/devicetree.c        |  2 ++
 drivers/power/power_supply_core.c   |  3 +++
 drivers/pwm/core.c                  |  3 +++
 drivers/regulator/core.c            | 45 +++++++++++++++----------------
 drivers/usb/phy/phy.c               |  3 +++
 drivers/video/backlight/backlight.c |  3 +++
 include/linux/of_platform.h         |  2 ++
 19 files changed, 130 insertions(+), 45 deletions(-)

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