[RFC 1/5] drivers: Add boot constraints core

Randy Dunlap
2017-06-28T15:55:08Z

On 06/28/2017 03:26 AM, Viresh Kumar wrote:
> Some devices are powered ON by the bootloaders 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 device 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 programmed so that all the users of them are satisfied. If
> some user (X) driver gets probed before the LCD controller driver in
> this case, then it may end up reconfiguring these resources to ranges
> satisfying the current users (only user X) and that can make the LCD
> screen unstable.
>
> This patch introduces the concept of boot-constraints, which will be set
> by the bootloaders and the kernel will satisfy them until the time
> driver for such a device is probed (successfully or unsuccessfully).
>
> The list of boot constraint types is empty for now, and will be added by
> a later patch.
>
> Only two routines are exposed by the boot constraints core for now:
>
> - boot_constraint_add(): This will be called by parts of the kernel
> (before the device is probed) to set the constraints.
>
> - boot_constraints_remove(): This is called only by the driver core
> after a device is probed successfully or unsuccessfully. Special
> handling is done here for deffered probing.
>
> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
> ---
> drivers/base/Kconfig | 11 +++
> drivers/base/Makefile | 1 +
> drivers/base/boot_constraint.c | 210 ++++++++++++++++++++++++++++++++++++++++
> drivers/base/dd.c | 20 ++--
> include/linux/boot_constraint.h | 28 ++++++
> 5 files changed, 263 insertions(+), 7 deletions(-)
> create mode 100644 drivers/base/boot_constraint.c
> create mode 100644 include/linux/boot_constraint.h
>
> diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
> index d718ae4b907a..d71217a91793 100644
> --- a/drivers/base/Kconfig
> +++ b/drivers/base/Kconfig
> @@ -339,4 +339,15 @@ config CMA_ALIGNMENT
>
> endif
>
> +config BOOT_CONSTRAINTS
> + bool "Boot constraints for devices"
> + default y

Why default y?

As Linus just wrote yesterday:

No. We've tried. The only sensible default (and that I try to enforce)
is "new featrures default to 'n'"

> + help
> + This enables boot constraints detection for devices. These constraints
> + are (normally) set by the Bootloader and must be satisfied by the
> + kernel until the relevant device driver is probed. Once the driver is
> + probed, the constraint is dropped.
> +
> + If unsure, say Y.
> +
> endmenu
> diff --git a/drivers/base/Makefile b/drivers/base/Makefile
> index f2816f6ff76a..6094b3b75184 100644
> --- a/drivers/base/Makefile
> +++ b/drivers/base/Makefile
> @@ -5,6 +5,7 @@ obj-y := component.o core.o bus.o dd.o syscore.o \
> cpu.o firmware.o init.o map.o devres.o \
> attribute_container.o transport_class.o \
> topology.o container.o property.o cacheinfo.o
> +obj-$(CONFIG_BOOT_CONSTRAINTS) += boot_constraint.o
> obj-$(CONFIG_DEVTMPFS) += devtmpfs.o
> obj-$(CONFIG_DMA_CMA) += dma-contiguous.o
> obj-y += power/

--
~Randy