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linux/arch/riscv/kernel/sbi-ipi.c

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RISC-V: Treat IPIs as normal Linux IRQs Currently, the RISC-V kernel provides arch specific hooks (i.e. struct riscv_ipi_ops) to register IPI handling methods. The stats gathering of IPIs is also arch specific in the RISC-V kernel. Other architectures (such as ARM, ARM64, and MIPS) have moved away from custom arch specific IPI handling methods. Currently, these architectures have Linux irqchip drivers providing a range of Linux IRQ numbers to be used as IPIs and IPI triggering is done using generic IPI APIs. This approach allows architectures to treat IPIs as normal Linux IRQs and IPI stats gathering is done by the generic Linux IRQ subsystem. We extend the RISC-V IPI handling as-per above approach so that arch specific IPI handling methods (struct riscv_ipi_ops) can be removed and the IPI handling is done through the Linux IRQ subsystem. Signed-off-by: Anup Patel <apatel@ventanamicro.com> Acked-by: Palmer Dabbelt <palmer@rivosinc.com> Signed-off-by: Marc Zyngier <maz@kernel.org> Link: https://lore.kernel.org/r/20230328035223.1480939-4-apatel@ventanamicro.com
2023-03-27 20:52:19 -07:00
// SPDX-License-Identifier: GPL-2.0-only
/*
* Multiplex several IPIs over a single HW IPI.
*
* Copyright (c) 2022 Ventana Micro Systems Inc.
*/
#define pr_fmt(fmt) "riscv: " fmt
#include <linux/cpu.h>
#include <linux/init.h>
#include <linux/irq.h>
#include <linux/irqchip/chained_irq.h>
#include <linux/irqdomain.h>
#include <asm/sbi.h>
riscv: Use IPIs for remote cache/TLB flushes by default An IPI backend is always required in an SMP configuration, but an SBI implementation is not. For example, SBI will be unavailable when the kernel runs in M mode. For this reason, consider IPI delivery of cache and TLB flushes to be the base case, and any other implementation (such as the SBI remote fence extension) to be an optimization. Generally, if IPIs can be delivered without firmware assistance, they are assumed to be faster than SBI calls due to the SBI context switch overhead. However, when SBI is used as the IPI backend, then the context switch cost must be paid anyway, and performing the cache/TLB flush directly in the SBI implementation is more efficient than injecting an interrupt to S-mode. This is the only existing scenario where riscv_ipi_set_virq_range() is called with use_for_rfence set to false. sbi_ipi_init() already checks riscv_ipi_have_virq_range(), so it only calls riscv_ipi_set_virq_range() when no other IPI device is available. This allows moving the static key and dropping the use_for_rfence parameter. This decouples the static key from the irqchip driver probe order. Furthermore, the static branch only makes sense when CONFIG_RISCV_SBI is enabled. Optherwise, IPIs must be used. Add a fallback definition of riscv_use_sbi_for_rfence() which handles this case and removes the need to check CONFIG_RISCV_SBI elsewhere, such as in cacheflush.c. Reviewed-by: Anup Patel <anup@brainfault.org> Signed-off-by: Samuel Holland <samuel.holland@sifive.com> Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com> Link: https://lore.kernel.org/r/20240327045035.368512-4-samuel.holland@sifive.com Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
2024-03-26 21:49:44 -07:00
DEFINE_STATIC_KEY_FALSE(riscv_sbi_for_rfence);
EXPORT_SYMBOL_GPL(riscv_sbi_for_rfence);
RISC-V: Treat IPIs as normal Linux IRQs Currently, the RISC-V kernel provides arch specific hooks (i.e. struct riscv_ipi_ops) to register IPI handling methods. The stats gathering of IPIs is also arch specific in the RISC-V kernel. Other architectures (such as ARM, ARM64, and MIPS) have moved away from custom arch specific IPI handling methods. Currently, these architectures have Linux irqchip drivers providing a range of Linux IRQ numbers to be used as IPIs and IPI triggering is done using generic IPI APIs. This approach allows architectures to treat IPIs as normal Linux IRQs and IPI stats gathering is done by the generic Linux IRQ subsystem. We extend the RISC-V IPI handling as-per above approach so that arch specific IPI handling methods (struct riscv_ipi_ops) can be removed and the IPI handling is done through the Linux IRQ subsystem. Signed-off-by: Anup Patel <apatel@ventanamicro.com> Acked-by: Palmer Dabbelt <palmer@rivosinc.com> Signed-off-by: Marc Zyngier <maz@kernel.org> Link: https://lore.kernel.org/r/20230328035223.1480939-4-apatel@ventanamicro.com
2023-03-27 20:52:19 -07:00
static int sbi_ipi_virq;
static void sbi_ipi_handle(struct irq_desc *desc)
{
struct irq_chip *chip = irq_desc_get_chip(desc);
chained_irq_enter(chip, desc);
csr_clear(CSR_IP, IE_SIE);
ipi_mux_process();
chained_irq_exit(chip, desc);
}
static int sbi_ipi_starting_cpu(unsigned int cpu)
{
enable_percpu_irq(sbi_ipi_virq, irq_get_trigger_type(sbi_ipi_virq));
return 0;
}
void __init sbi_ipi_init(void)
{
int virq;
struct irq_domain *domain;
if (riscv_ipi_have_virq_range())
return;
domain = irq_find_matching_fwnode(riscv_get_intc_hwnode(),
DOMAIN_BUS_ANY);
if (!domain) {
pr_err("unable to find INTC IRQ domain\n");
return;
}
sbi_ipi_virq = irq_create_mapping(domain, RV_IRQ_SOFT);
if (!sbi_ipi_virq) {
pr_err("unable to create INTC IRQ mapping\n");
return;
}
virq = ipi_mux_create(BITS_PER_BYTE, sbi_send_ipi);
if (virq <= 0) {
pr_err("unable to create muxed IPIs\n");
irq_dispose_mapping(sbi_ipi_virq);
return;
}
irq_set_chained_handler(sbi_ipi_virq, sbi_ipi_handle);
/*
* Don't disable IPI when CPU goes offline because
* the masking/unmasking of virtual IPIs is done
* via generic IPI-Mux
*/
RISC-V: Enable the IPI before workqueue_online_cpu() Sometimes the hotplug cpu stalls at the arch_cpu_idle() for a while after workqueue_online_cpu(). When cpu stalls at the idle loop, the reschedule IPI is pending. However the enable bit is not enabled yet so the cpu stalls at WFI until watchdog timeout. Therefore enable the IPI before the workqueue_online_cpu() to fix the issue. Fixes: 63c5484e7495 ("workqueue: Add multiple affinity scopes and interface to select them") Signed-off-by: Nick Hu <nick.hu@sifive.com> Reviewed-by: Anup Patel <anup@brainfault.org> Link: https://lore.kernel.org/r/20240717031714.1946036-1-nick.hu@sifive.com Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
2024-07-16 20:17:14 -07:00
cpuhp_setup_state(CPUHP_AP_IRQ_RISCV_SBI_IPI_STARTING,
RISC-V: Treat IPIs as normal Linux IRQs Currently, the RISC-V kernel provides arch specific hooks (i.e. struct riscv_ipi_ops) to register IPI handling methods. The stats gathering of IPIs is also arch specific in the RISC-V kernel. Other architectures (such as ARM, ARM64, and MIPS) have moved away from custom arch specific IPI handling methods. Currently, these architectures have Linux irqchip drivers providing a range of Linux IRQ numbers to be used as IPIs and IPI triggering is done using generic IPI APIs. This approach allows architectures to treat IPIs as normal Linux IRQs and IPI stats gathering is done by the generic Linux IRQ subsystem. We extend the RISC-V IPI handling as-per above approach so that arch specific IPI handling methods (struct riscv_ipi_ops) can be removed and the IPI handling is done through the Linux IRQ subsystem. Signed-off-by: Anup Patel <apatel@ventanamicro.com> Acked-by: Palmer Dabbelt <palmer@rivosinc.com> Signed-off-by: Marc Zyngier <maz@kernel.org> Link: https://lore.kernel.org/r/20230328035223.1480939-4-apatel@ventanamicro.com
2023-03-27 20:52:19 -07:00
"irqchip/sbi-ipi:starting",
sbi_ipi_starting_cpu, NULL);
riscv: Use IPIs for remote cache/TLB flushes by default An IPI backend is always required in an SMP configuration, but an SBI implementation is not. For example, SBI will be unavailable when the kernel runs in M mode. For this reason, consider IPI delivery of cache and TLB flushes to be the base case, and any other implementation (such as the SBI remote fence extension) to be an optimization. Generally, if IPIs can be delivered without firmware assistance, they are assumed to be faster than SBI calls due to the SBI context switch overhead. However, when SBI is used as the IPI backend, then the context switch cost must be paid anyway, and performing the cache/TLB flush directly in the SBI implementation is more efficient than injecting an interrupt to S-mode. This is the only existing scenario where riscv_ipi_set_virq_range() is called with use_for_rfence set to false. sbi_ipi_init() already checks riscv_ipi_have_virq_range(), so it only calls riscv_ipi_set_virq_range() when no other IPI device is available. This allows moving the static key and dropping the use_for_rfence parameter. This decouples the static key from the irqchip driver probe order. Furthermore, the static branch only makes sense when CONFIG_RISCV_SBI is enabled. Optherwise, IPIs must be used. Add a fallback definition of riscv_use_sbi_for_rfence() which handles this case and removes the need to check CONFIG_RISCV_SBI elsewhere, such as in cacheflush.c. Reviewed-by: Anup Patel <anup@brainfault.org> Signed-off-by: Samuel Holland <samuel.holland@sifive.com> Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com> Link: https://lore.kernel.org/r/20240327045035.368512-4-samuel.holland@sifive.com Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
2024-03-26 21:49:44 -07:00
riscv_ipi_set_virq_range(virq, BITS_PER_BYTE);
RISC-V: Treat IPIs as normal Linux IRQs Currently, the RISC-V kernel provides arch specific hooks (i.e. struct riscv_ipi_ops) to register IPI handling methods. The stats gathering of IPIs is also arch specific in the RISC-V kernel. Other architectures (such as ARM, ARM64, and MIPS) have moved away from custom arch specific IPI handling methods. Currently, these architectures have Linux irqchip drivers providing a range of Linux IRQ numbers to be used as IPIs and IPI triggering is done using generic IPI APIs. This approach allows architectures to treat IPIs as normal Linux IRQs and IPI stats gathering is done by the generic Linux IRQ subsystem. We extend the RISC-V IPI handling as-per above approach so that arch specific IPI handling methods (struct riscv_ipi_ops) can be removed and the IPI handling is done through the Linux IRQ subsystem. Signed-off-by: Anup Patel <apatel@ventanamicro.com> Acked-by: Palmer Dabbelt <palmer@rivosinc.com> Signed-off-by: Marc Zyngier <maz@kernel.org> Link: https://lore.kernel.org/r/20230328035223.1480939-4-apatel@ventanamicro.com
2023-03-27 20:52:19 -07:00
pr_info("providing IPIs using SBI IPI extension\n");
riscv: Use IPIs for remote cache/TLB flushes by default An IPI backend is always required in an SMP configuration, but an SBI implementation is not. For example, SBI will be unavailable when the kernel runs in M mode. For this reason, consider IPI delivery of cache and TLB flushes to be the base case, and any other implementation (such as the SBI remote fence extension) to be an optimization. Generally, if IPIs can be delivered without firmware assistance, they are assumed to be faster than SBI calls due to the SBI context switch overhead. However, when SBI is used as the IPI backend, then the context switch cost must be paid anyway, and performing the cache/TLB flush directly in the SBI implementation is more efficient than injecting an interrupt to S-mode. This is the only existing scenario where riscv_ipi_set_virq_range() is called with use_for_rfence set to false. sbi_ipi_init() already checks riscv_ipi_have_virq_range(), so it only calls riscv_ipi_set_virq_range() when no other IPI device is available. This allows moving the static key and dropping the use_for_rfence parameter. This decouples the static key from the irqchip driver probe order. Furthermore, the static branch only makes sense when CONFIG_RISCV_SBI is enabled. Optherwise, IPIs must be used. Add a fallback definition of riscv_use_sbi_for_rfence() which handles this case and removes the need to check CONFIG_RISCV_SBI elsewhere, such as in cacheflush.c. Reviewed-by: Anup Patel <anup@brainfault.org> Signed-off-by: Samuel Holland <samuel.holland@sifive.com> Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com> Link: https://lore.kernel.org/r/20240327045035.368512-4-samuel.holland@sifive.com Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
2024-03-26 21:49:44 -07:00
/*
* Use the SBI remote fence extension to avoid
* the extra context switch needed to handle IPIs.
*/
static_branch_enable(&riscv_sbi_for_rfence);
RISC-V: Treat IPIs as normal Linux IRQs Currently, the RISC-V kernel provides arch specific hooks (i.e. struct riscv_ipi_ops) to register IPI handling methods. The stats gathering of IPIs is also arch specific in the RISC-V kernel. Other architectures (such as ARM, ARM64, and MIPS) have moved away from custom arch specific IPI handling methods. Currently, these architectures have Linux irqchip drivers providing a range of Linux IRQ numbers to be used as IPIs and IPI triggering is done using generic IPI APIs. This approach allows architectures to treat IPIs as normal Linux IRQs and IPI stats gathering is done by the generic Linux IRQ subsystem. We extend the RISC-V IPI handling as-per above approach so that arch specific IPI handling methods (struct riscv_ipi_ops) can be removed and the IPI handling is done through the Linux IRQ subsystem. Signed-off-by: Anup Patel <apatel@ventanamicro.com> Acked-by: Palmer Dabbelt <palmer@rivosinc.com> Signed-off-by: Marc Zyngier <maz@kernel.org> Link: https://lore.kernel.org/r/20230328035223.1480939-4-apatel@ventanamicro.com
2023-03-27 20:52:19 -07:00
}
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