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.ku...@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
