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From:   Rob Herring <robh+dt@kernel.org>
Date:   Mon, 30 Oct 2017 17:07:53 -0500
Message-ID: <CAL_JsqKi+9yEXRq=XcCG=S8wXmLk9BFCnXWEE9mcf+495j+1sw@mail.gmail.com>
Subject: Re: [PATCH V4 00/12] drivers: Boot Constraints core
To:     Viresh Kumar <viresh.kumar@linaro.org>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Stephen Boyd <sboyd@codeaurora.org>,
        Rajendra Nayak <rnayak@codeaurora.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        Rob Clark <robdclark@gmail.com>,
        Sascha Hauer <s.hauer@pengutronix.de>,
        Lucas Stach <l.stach@pengutronix.de>,
        Shawn Guo <shawnguo@kernel.org>,
        Fabio Estevam <fabio.estevam@nxp.com>,
        Nishanth Menon <nm@ti.com>, Wei Xu <xuwei5@hisilicon.com>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        Frank Rowand <frowand.list@gmail.com>
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On Sun, Oct 29, 2017 at 8:48 AM, Viresh Kumar <viresh.kumar@linaro.org> wrote:
> Hi Greg,
>
> Here is V4 of the boot constraints core based on your feedback from V3.
> We now have support for three platforms (as you suggested) included in
> this series: Hisilicon, IMX and Qualcomm.
>
> I have tested the Hisilicon patches on hikey 9660 board, IMX stuff is
> tested by Sascha (Pengutronix) on i.MX6 and Qualcomm stuff is tested by
> Rajendra (Qualcomm) on Dragonboard 410C (This required some more patches
> related to display driver which Rajendra should be sending separately
> later on).
>
>
> Problem statement:
>
> Some devices are powered ON by the bootloader before the bootloader
> handovers control to Linux. It maybe important for those devices to keep
> working until the time a Linux device driver probes the device and
> reconfigure its resources.
>
> A typical example of that can be the LCD controller, which is used by
> the bootloaders to show image(s) while the platform is booting into
> Linux.  The LCD controller can be using some resources, like clk,
> regulators, etc, that are shared between several devices. These shared
> resources should be configured to satisfy need of all the users.  If
> another device's (X) driver gets probed before the LCD controller driver
> in this case, then it may end up disabling or reconfiguring these
> resources to ranges satisfying the current users (only device X) and
> that can make the LCD screen unstable.

Would probing the display earlier solve this as that's also something
people care about (or work-around by initializing the display in the
bootloader). I guess if the display depends on resources A, B, and C,
other drivers could still each only depend on one of those and probe
successfully before the display does. However, the display driver
would still probe, so you could do something then to enable the
constraints. That would have the advantage that the driver knows what
resources it needs even if probe is deferred and you don't need
special DT bindings nor platform code.

Getting certain drivers/devices to probe first may just require
ensuring they get inserted at the beginning of the driver and device
lists which would be a pretty trivial change I think. That's ignoring
differing initcall levels though.

> Another case can be a debug serial port enabled from the bootloader.

Continuing the above thought, we could just match device nodes against
stdout-path as we create devices and then set a priority flag or
something that the driver core would handle.

Yes, it's triggered by a specific use case, but I'm not that convinced
that having things setup by the bootloader and needing a transparent
hand off is a general case. You've given 2 examples. I can't think of
many more. One is CAN bus which has realtime servicing requirements,
but I don't think this series solves that (OOT solutions I've seen
insert callbacks at random places during kernel init). The other case
is just things that have no driver at all, but resources need to
remain enabled. That should just be some platform code to enable those
things IMO.

> Of course we can have more complex cases where the same resource is
> getting used by two devices while the kernel boots and the order in
> which devices get probed wouldn't matter as the other device will surely
> break then.
>
> There are also cases where the resources may not be shared, but the
> kernel will disable them forcefully as no users may have appeared until
> a certain point in kernel boot. This makes sure that the resources stay
> enabled. A wide variety of constraints can be satisfied using the new
> framework.

This is only if the driver (or dependent driver) is a module though.
Is that something we really need to handle?

>
> Proposed solution:
>
> This series introduces the concept of "boot-constraints", which are set
> by platform specific drivers (for now at least) at early init (like
> subsys_initcall) and the kernel will keep satisfying them until the time
> driver for such a device is probed (successfully or unsuccessfully).
> Once the driver is probed, the driver core removes the constraints set
> for the device. This series implements clk, regulator and PM domain
> constraints currently.
>
> Rebased over: driver-core/master
> Targeted for: v4.16 (Sending it earlier for reviews mostly)
>
> Pushed here:
> git://git.kernel.org/pub/scm/linux/kernel/git/vireshk/linux.git device/boot-constraints
>
> V3->V4:
> - Added support for imx, hikey and Qcom usecases.
> - Enhanced boot constraints core to make drivers code easy and handle
>   complex cases.
> - Two new patches for OF included to provide APIs to boot constraint
>   core.
> - Removed the kernel parameter patch for now.
> - Don't check return values of debugfs routines.
> - Moved the boot constraints core from drivers/base/ to drivers/.
>
> V2->V3:
> - Removed DT support as we aren't sure about how to define the bindings
>   yet.
> - Added CLK and PM domain constraint types.
> - A new directory is added for boot constraints, which will also contain
>   platform specific drivers in future.
> - Deferred devices are still supported, just that it wouldn't be called
>   from generic code anymore but platform specific code.
> - Tested on Qcom 410c dragonboard with display flash screen (Rajendra).
> - Usual renaming/commit-log-updates/etc changes done.
>
> V1->V2:
> - Add support for setting constraints for devices created from DT.
> - Allow handling deferred devices earlier then late_init.
> - Remove 'default y' line from kconfig.
> - Drop '=" after boot_constraints_disable kernel param.
> - Dropped the dummy testing patch now.
>
> --
> viresh
>
> Rajendra Nayak (1):
>   boot_constraint: Add Qualcomm display controller constraints
>
> Viresh Kumar (11):
>   of: platform: Add of_find_amba_device_by_node()
>   of: platform: Make of_platform_bus_create() global
>   drivers: Add boot constraints core
>   boot_constraint: Add support for supply constraints
>   boot_constraint: Add support for clk constraints
>   boot_constraint: Add support for PM constraints
>   boot_constraint: Add debugfs support
>   boot_constraint: Manage deferrable constraints
>   boot_constraint: Add earlycon helper
>   boot_constraint: Add support for Hisilicon platforms
>   boot_constraint: Add support for IMX platform
>
>  arch/arm/mach-imx/Kconfig                 |   1 +
>  arch/arm64/Kconfig.platforms              |   2 +
>  drivers/Kconfig                           |   2 +
>  drivers/Makefile                          |   1 +
>  drivers/base/dd.c                         |  32 +++-
>  drivers/boot_constraints/Kconfig          |   9 +
>  drivers/boot_constraints/Makefile         |   7 +

Maintainer for this?

>  drivers/boot_constraints/clk.c            |  73 ++++++++
>  drivers/boot_constraints/core.c           | 271 ++++++++++++++++++++++++++++++
>  drivers/boot_constraints/core.h           |  48 ++++++
>  drivers/boot_constraints/deferrable_dev.c | 235 ++++++++++++++++++++++++++
>  drivers/boot_constraints/hikey.c          | 145 ++++++++++++++++
>  drivers/boot_constraints/imx.c            | 113 +++++++++++++
>  drivers/boot_constraints/pm.c             |  31 ++++
>  drivers/boot_constraints/qcom.c           | 123 ++++++++++++++
>  drivers/boot_constraints/serial.c         |  28 +++

earlycon really. earlycon doesn't have to be a serial device.

>  drivers/boot_constraints/supply.c         | 107 ++++++++++++

Kind of a mixture of boards and subsystem handlers. Perhaps subsystem
handlers should go into the subsystems. Then you can get a lot more
opinions on this. :)


>  drivers/clk/imx/clk-imx25.c               |  12 --
>  drivers/clk/imx/clk-imx27.c               |  13 --
>  drivers/clk/imx/clk-imx31.c               |  12 --
>  drivers/clk/imx/clk-imx35.c               |  10 --
>  drivers/clk/imx/clk-imx51-imx53.c         |  16 --
>  drivers/clk/imx/clk-imx6q.c               |   8 -
>  drivers/clk/imx/clk-imx6sl.c              |   8 -
>  drivers/clk/imx/clk-imx6sx.c              |   8 -
>  drivers/clk/imx/clk-imx7d.c               |  14 --
>  drivers/clk/imx/clk.c                     |  38 -----
>  drivers/clk/imx/clk.h                     |   1 -
>  drivers/of/platform.c                     |  28 ++-
>  include/linux/boot_constraint.h           |  74 ++++++++
>  include/linux/of_platform.h               |  21 +++
>  31 files changed, 1340 insertions(+), 151 deletions(-)
>  create mode 100644 drivers/boot_constraints/Kconfig
>  create mode 100644 drivers/boot_constraints/Makefile
>  create mode 100644 drivers/boot_constraints/clk.c
>  create mode 100644 drivers/boot_constraints/core.c
>  create mode 100644 drivers/boot_constraints/core.h
>  create mode 100644 drivers/boot_constraints/deferrable_dev.c
>  create mode 100644 drivers/boot_constraints/hikey.c
>  create mode 100644 drivers/boot_constraints/imx.c
>  create mode 100644 drivers/boot_constraints/pm.c
>  create mode 100644 drivers/boot_constraints/qcom.c
>  create mode 100644 drivers/boot_constraints/serial.c
>  create mode 100644 drivers/boot_constraints/supply.c
>  create mode 100644 include/linux/boot_constraint.h
>
> --
> 2.15.0.rc1.236.g92ea95045093
>

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