IRQ controllers and timers are the two types of device the kernel requires before being able to use the device driver model.
The Device Tree infrastructure makes it very easy to make these discoverable by the rest of the kernel. For example, each interrupt controller driver has at least one entry like this:
IRQCHIP_DECLARE(gic_400, "arm,gic-400", gic_of_init);
which says: if you find a node having "arm,gic-400" as a compatible string in the device tree, then call gic_of_init with this node as a parameter. The probing itself is done by the OF layer when the architecture code calls of_irq_init() (usually via irqchip_init).
This has a number of benefits:
- The irqchip code is self-contained. No architecture specific entry point, no exposed symbols. Just a standard interface.
- The low-level architecture code doesn't have to know about which interrupt controller is present. It just calls into the firmware interface (of_irq_init) which is going to sort things out.
Similar infrastructure is provided for the timers/clock sources. Note that this is not a replacement for the device model, but acts as a probing infrastructure for things that are required too early for the device infrastructure to be available.
What I'm aiming for is to introduce the same level of abstraction for ACPI, or at least for the few bits that are required before a full blown ACPI/device model can be used. For this, I introduce something vaguely similar:
IRQCHIP_ACPI_DECLARE(gic_v2, ACPI_MADT_TYPE_GENERIC_DISTRIBUTOR, gic_validate_dist, ACPI_MADT_GIC_VERSION_V2, gic_v2_acpi_init);
which says: if you find a ACPI_MADT_TYPE_GENERIC_DISTRIBUTOR entry in MADT (implied by the macro), and that entry is of type ACPI_MADT_GIC_VERSION_V2 (as checked by gic_validate_dist), then call gic_v2_acpi_init with the entry as a parameter. A bit more convoluted, but still without any special entry point.
The various interrupt controller drivers can then implement the above, and the arch code can use a firmware-specific call to get the probing done, still oblivious to what interrupt controller is being used. It also makes the adaptation of a DT driver to ACPI easier.
It turns out that providing such a probing infrastructure is rather easy, and provides a much deserved cleanup in both the arch code, the GIC driver, and the architected timer driver. An additional (and very much optional) patch renames files and symbols to make it obvious that the infrastructure is not just for DT anymore.
I'm sure there is some more code to be deleted, and one can only wonder why this wasn't done before the arm64 code was initially merged (the diffstat says it all...).
Patches are against Rafael's bleeding-edge branch, and a branch is available at
git://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git acpi/device-probing-v3
* From v2: - Addressed Rafael's comments (title for patch #1, macro/field names) - New config symbols for clocksources - Additional and optional last patch to get rid of the apparent dependency between the probing infrastructure and DT.
* From the initial version: - Make the infrastructure more DT like by providing an acpi_probe_entry array per "device type" (one for irqchips, one for clocksources). This means that entries can depend on any ACPI static table. - Use some cpp magic to reduce the amount of code added to an absolute minimum. - Rebased on v4.3-rc1
Marc Zyngier (7): acpi: Add early device probing infrastructure irqchip/acpi: Add probing infrastructure for ACPI-based irqchips irqchip/gic: Convert the GIC driver to ACPI probing clocksource/acpi: Add probing infrastructure for ACPI-based clocksources clocksource: Add new CLKSRC_{PROBE,ACPI} config symbols clocksource/arm_arch_timer: Convert to ACPI probing clocksource: cosmetic: Drop OF 'dependency' from symbols
arch/arm/kernel/time.c | 2 +- arch/arm/mach-omap2/timer.c | 4 +- arch/arm/mach-rockchip/rockchip.c | 2 +- arch/arm/mach-shmobile/setup-r8a7779.c | 2 +- arch/arm/mach-shmobile/setup-rcar-gen2.c | 2 +- arch/arm/mach-spear/spear13xx.c | 2 +- arch/arm/mach-sunxi/sunxi.c | 2 +- arch/arm/mach-u300/core.c | 2 +- arch/arm/mach-ux500/timer.c | 2 +- arch/arm/mach-zynq/common.c | 2 +- arch/arm64/include/asm/acpi.h | 1 - arch/arm64/include/asm/irq.h | 13 ---- arch/arm64/kernel/acpi.c | 25 -------- arch/arm64/kernel/time.c | 8 +-- arch/microblaze/kernel/setup.c | 2 +- arch/mips/pistachio/time.c | 2 +- arch/mips/ralink/clk.c | 2 +- arch/nios2/kernel/time.c | 2 +- arch/xtensa/kernel/time.c | 2 +- drivers/acpi/scan.c | 39 ++++++++++++ drivers/clocksource/Kconfig | 9 +++ drivers/clocksource/Makefile | 2 +- drivers/clocksource/arm_arch_timer.c | 10 +--- .../clocksource/{clksrc-of.c => clksrc-probe.c} | 6 +- drivers/irqchip/irq-gic.c | 69 +++++++++++----------- drivers/irqchip/irqchip.c | 5 +- include/asm-generic/vmlinux.lds.h | 12 ++++ include/linux/acpi.h | 66 +++++++++++++++++++++ include/linux/acpi_irq.h | 10 ---- include/linux/clocksource.h | 13 ++-- include/linux/irqchip.h | 17 ++++++ include/linux/irqchip/arm-gic-acpi.h | 31 ---------- 32 files changed, 209 insertions(+), 159 deletions(-) rename drivers/clocksource/{clksrc-of.c => clksrc-probe.c} (91%) delete mode 100644 include/linux/acpi_irq.h delete mode 100644 include/linux/irqchip/arm-gic-acpi.h