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

Rob Herring
2015-05-28T04:34:09Z

On Mon, May 25, 2015 at 9:53 AM, Tomeu Vizoso
<tomeu.vizoso@collabora.com> 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(-)
>
> --
> 2.4.1
>