[PATCH v14 0/8] RISC-V IPI Improvements

Anup Patel
2022-12-01T13:02:23Z

This series aims to improve IPI support in Linux RISC-V in following ways:
1) Treat IPIs as normal per-CPU interrupts instead of having custom RISC-V
specific hooks. This also makes Linux RISC-V IPI support aligned with
other architectures.
2) Remote TLB flushes and icache flushes should prefer local IPIs instead
of SBI calls whenever we have specialized hardware (such as RISC-V AIA
IMSIC and RISC-V SWI) which allows S-mode software to directly inject
IPIs without any assistance from M-mode runtime firmware.

These patches were originally part of the "Linux RISC-V ACLINT Support"
series but this now a separate series so that it can be merged independently
of the "Linux RISC-V ACLINT Support" series.
(Refer, https://lore.kernel.org/lkml/20211007123632.697666-1-anup.patel@wdc.com/)

These patches are also a preparatory patches for the up-coming:
1) Linux RISC-V AIA support
2) Linux RISC-V SWI support

These patches can also be found in riscv_ipi_imp_v14 branch at:
https://github.com/avpatel/linux.git

Changes since v13:
- Included changes suggested by Marc Z in PATCH3
- Use chained handlers in PATCH4
- Added new PATCH8 to have empty irq_eoi() in RISC-V INTC driver. This
avoids the unnecessary mask/unmask dance at time of handling interrupts.

Changes since v12:
- Rebased on Linux-6.1-rc7
- Bring-back the IPI optimization in ipi_mux_send_mask() for PATCH3
- Call ipi_mux_send() for one target CPU at a time in PATCH3

Changes since v11:
- Removed ipi_mux_pre/post_handle() callbacks in PATCH3
- Removed sturct ipi_mux_ops in PATCH3
- Removed parent_virq and data pointer from everywhere in PATCH3
- Removed struct ipi_mux_control in PATCH3
- Improved function signature of ipi_mux_send() callback in PATCH3
- Used unsigned type with atomic operation in PATCH3

Changes since v10:
- Rebased on Linux-6.1-rc5
- Drop the "!(pending & ibit)" check in ipi_mux_send_mask() of PATCH3
- Disable local interrupts in ipi_mux_send_mask() of PATCH3 because we
can be preempted while using a per-CPU temporary variable.

Changes since v9:
- Rebased on Linux-6.1-rc3
- Updated header comment block of ipi-mux.c in PATCH3
- Use a struct for global data of ipi-mux.c in PATCH3
- Add per-CPU temp cpumask for sending IPIs in PATCH3
- Drop the use of fwspec in PATCH3
- Use static key for ipi_mux_pre_handle() and ipi_mux_post_handle()
in PATCH3
- Remove redundant pr_warn_ratelimited() called by ipi_mux_process()
in PATCH3
- Remove CPUHP thingy from ipi_mux_create() in PATCH3

Changes since v8:
- Rebased on Linux-6.0-rc3
- Use dummy percpu data as parameter for request_percpu_irq() in PATCH4.

Changes since v7:
- Rebased on Linux-6.0-rc1
- Use atomic operations to track per-CPU pending and enabled IPIs in PATCH3.
(Note: this is inspired from IPI muxing implemented in
drivers/irqchip/irq-apple-aic.c)
- Made "struct ipi_mux_ops" (added by PATCH3) flexible so that
drivers/irqchip/irq-apple-aic.c can adopt it in future.

Changes since v6:
- Rebased on Linux-5.19-rc7
- Added documentation for struct ipi_mux_ops in PATCH3
- Dropped dummy irq_mask()/unmask() in PATCH3
- Added const for "ipi_mux_chip" in PATCH3
- Removed "type" initialization from ipi_mux_domain_alloc() in PATCH3
- Dropped translate() from "ipi_mux_domain_ops" in PATCH3
- Improved barrier documentation in ipi_mux_process() of PATCH3
- Added percpu check in ipi_mux_create() for parent_virq of PATCH3
- Added nr_ipi parameter in ipi_mux_create() of PATCH3

Changes since v5:
- Rebased on Linux-5.18-rc3
- Used kernel doc style in PATCH3
- Removed redundant loop in ipi_mux_process() of PATCH3
- Removed "RISC-V" prefix form ipi_mux_chip.name of PATCH3
- Removed use of "this patch" in PATCH3 commit description
- Addressed few other nit comments in PATCH3

Changes since v4:
- Rebased on Linux-5.17
- Includes new PATCH3 which adds mechanism to multiplex a single HW IPI

Changes since v3:
- Rebased on Linux-5.17-rc6
- Updated PATCH2 to not export riscv_set_intc_hwnode_fn()
- Simplified riscv_intc_hwnode() in PATCH2

Changes since v2:
- Rebased on Linux-5.17-rc4
- Updated PATCH2 to not create synthetic INTC fwnode and instead provide
a function which allows drivers to directly discover INTC fwnode

Changes since v1:
- Use synthetic fwnode for INTC instead of irq_set_default_host() in PATCH2

Anup Patel (8):
RISC-V: Clear SIP bit only when using SBI IPI operations
irqchip/riscv-intc: Allow drivers to directly discover INTC hwnode
genirq: Add mechanism to multiplex a single HW IPI
RISC-V: Treat IPIs as normal Linux IRQs
RISC-V: Allow marking IPIs as suitable for remote FENCEs
RISC-V: Use IPIs for remote TLB flush when possible
RISC-V: Use IPIs for remote icache flush when possible
irqchip/riscv-intc: Add empty irq_eoi() for chained irq handlers

arch/riscv/Kconfig | 2 +
arch/riscv/include/asm/irq.h | 4 +
arch/riscv/include/asm/sbi.h | 10 +-
arch/riscv/include/asm/smp.h | 49 +++++---
arch/riscv/kernel/Makefile | 1 +
arch/riscv/kernel/cpu-hotplug.c | 3 +-
arch/riscv/kernel/irq.c | 21 +++-
arch/riscv/kernel/sbi-ipi.c | 77 ++++++++++++
arch/riscv/kernel/sbi.c | 100 +++------------
arch/riscv/kernel/smp.c | 166 +++++++++++++------------
arch/riscv/kernel/smpboot.c | 5 +-
arch/riscv/mm/cacheflush.c | 5 +-
arch/riscv/mm/tlbflush.c | 93 +++++++++++---
drivers/clocksource/timer-clint.c | 61 ++++++---
drivers/irqchip/Kconfig | 1 +
drivers/irqchip/irq-riscv-intc.c | 71 +++++++----
include/linux/irq.h | 3 +
kernel/irq/Kconfig | 5 +
kernel/irq/Makefile | 1 +
kernel/irq/ipi-mux.c | 199 ++++++++++++++++++++++++++++++
20 files changed, 633 insertions(+), 244 deletions(-)
create mode 100644 arch/riscv/kernel/sbi-ipi.c
create mode 100644 kernel/irq/ipi-mux.c

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2.34.1