On Sun, Jun 13, 2021 at 3:11 PM Marc Zyngier [off-list ref] wrote:

On Sat, 12 Jun 2021 17:04:17 +0100,
Anup Patel [off-list ref] wrote:

quoted

The RISC-V ACLINT provides MSWI and SSWI devices for M-mode and
S-mode software interrupts respectively. We add irqchip driver
which provide IPI operations based on ACLINT [M|S]SWI devices
to the Linux RISC-V kernel.

Signed-off-by: Anup Patel <redacted>
---
 drivers/irqchip/Kconfig          |  11 +++
 drivers/irqchip/Makefile         |   1 +
 drivers/irqchip/irq-aclint-swi.c | 122 +++++++++++++++++++++++++++++++
 3 files changed, 134 insertions(+)
 create mode 100644 drivers/irqchip/irq-aclint-swi.c

diff --git a/drivers/irqchip/Kconfig b/drivers/irqchip/Kconfig
index 62543a4eccc0..2010d493b03b 100644
--- a/drivers/irqchip/Kconfig
+++ b/drivers/irqchip/Kconfig

@@ -508,6 +508,17 @@ config RISCV_INTC

         If you don't know what to do here, say Y.

+config RISCV_ACLINT_SWI
+     bool "RISC-V Advanced Core Local Interruptor Software Interrupts"
+     depends on RISCV
+     help
+        This enables support for software interrupts using the Advanced
+        Core Local Interruptor (ACLINT) found in RISC-V systems.  The
+        RISC-V ACLINT provides devices for inter-process interrupt and
+        timer functionality.
+
+        If you don't know what to do here, say Y.
+
 config SIFIVE_PLIC
      bool "SiFive Platform-Level Interrupt Controller"
      depends on RISCV

diff --git a/drivers/irqchip/Makefile b/drivers/irqchip/Makefile
index f88cbf36a9d2..a6edf6733c1d 100644
--- a/drivers/irqchip/Makefile
+++ b/drivers/irqchip/Makefile

@@ -97,6 +97,7 @@ obj-$(CONFIG_QCOM_PDC)                      += qcom-pdc.o
 obj-$(CONFIG_CSKY_MPINTC)            += irq-csky-mpintc.o
 obj-$(CONFIG_CSKY_APB_INTC)          += irq-csky-apb-intc.o
 obj-$(CONFIG_RISCV_INTC)             += irq-riscv-intc.o
+obj-$(CONFIG_RISCV_ACLINT_SWI)               += irq-aclint-swi.o
 obj-$(CONFIG_SIFIVE_PLIC)            += irq-sifive-plic.o
 obj-$(CONFIG_IMX_IRQSTEER)           += irq-imx-irqsteer.o
 obj-$(CONFIG_IMX_INTMUX)             += irq-imx-intmux.o

diff --git a/drivers/irqchip/irq-aclint-swi.c b/drivers/irqchip/irq-aclint-swi.c
new file mode 100644
index 000000000000..f9607072cc7b
--- /dev/null
+++ b/drivers/irqchip/irq-aclint-swi.c

@@ -0,0 +1,122 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2021 Western Digital Corporation or its affiliates.
+ */
+
+#define pr_fmt(fmt) "aclint-swi: " fmt
+#include <linux/cpu.h>
+#include <linux/interrupt.h>
+#include <linux/io.h>
+#include <linux/irq.h>
+#include <linux/irqchip.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_address.h>
+#include <linux/of_irq.h>
+#include <linux/smp.h>
+
+struct aclint_swi {
+     void __iomem *sip_reg;
+};
+static DEFINE_PER_CPU(struct aclint_swi, aclint_swis);
+
+static void aclint_swi_send_ipi(const struct cpumask *target)
+{
+     unsigned int cpu;
+     struct aclint_swi *swi;
+
+     for_each_cpu(cpu, target) {
+             swi = per_cpu_ptr(&aclint_swis, cpu);
+             if (!swi->sip_reg) {
+                     pr_warn("%s: CPU%d SIP register not available\n",
+                             __func__, cpu);
+                     continue;
+             }
+
+             writel(1, swi->sip_reg);
+     }
+}
+
+static void aclint_swi_clear_ipi(void)
+{
+     struct aclint_swi *swi = this_cpu_ptr(&aclint_swis);
+
+     if (!swi->sip_reg) {
+             pr_warn("%s: CPU%d SIP register not available\n",
+                     __func__, smp_processor_id());
+             return;
+     }
+
+     writel(0, swi->sip_reg);
+}
+
+static struct riscv_ipi_ops aclint_swi_ipi_ops = {
+     .name = "ACLINT-SWI",
+     .use_for_rfence = true,
+     .ipi_inject = aclint_swi_send_ipi,
+     .ipi_clear = aclint_swi_clear_ipi,
+};
+
+static int __init aclint_swi_init(struct device_node *node,
+                               struct device_node *parent)
+{
+     void __iomem *base;
+     struct aclint_swi *swi;
+     u32 i, nr_irqs, nr_cpus = 0;
+
+     /* Map the registers */
+     base = of_iomap(node, 0);
+     if (!base) {
+             pr_err("%pOFP: could not map registers\n", node);
+             return -ENODEV;
+     }
+
+     /* Iterarte over each target CPU connected with this ACLINT */
+     nr_irqs = of_irq_count(node);
+     for (i = 0; i < nr_irqs; i++) {
+             struct of_phandle_args parent;
+             int cpu, hartid;
+
+             if (of_irq_parse_one(node, i, &parent)) {
+                     pr_err("%pOFP: failed to parse irq %d.\n",
+                            node, i);
+                     continue;
+             }
+
+             if (parent.args[0] != RV_IRQ_SOFT) {
+                     pr_err("%pOFP: invalid irq %d (hwirq %d)\n",
+                            node, i, parent.args[0]);
+                     continue;
+             }
+
+             hartid = riscv_of_parent_hartid(parent.np);
+             if (hartid < 0) {
+                     pr_warn("failed to parse hart ID for irq %d.\n", i);
+                     continue;
+             }
+
+             cpu = riscv_hartid_to_cpuid(hartid);
+             if (cpu < 0) {
+                     pr_warn("Invalid cpuid for irq %d\n", i);
+                     continue;
+             }
+
+             swi = per_cpu_ptr(&aclint_swis, cpu);
+             swi->sip_reg = base + i * sizeof(u32);
+             nr_cpus++;
+     }
+
+     /* Announce the ACLINT SWI device */
+     pr_info("%pOFP: providing IPIs for %d CPUs\n", node, nr_cpus);
+
+     /* Register the IPI operations */
+     riscv_set_ipi_ops(&aclint_swi_ipi_ops);
+
+     return 0;
+}
+
+#ifdef CONFIG_RISCV_M_MODE
+IRQCHIP_DECLARE(riscv_aclint_swi, "riscv,aclint-mswi", aclint_swi_init);
+#else
+IRQCHIP_DECLARE(riscv_aclint_swi, "riscv,aclint-sswi", aclint_swi_init);
+#endif

I'm sorry, but this really isn't an irqchip driver. This is a piece of
arch-specific code that uses *none* of the irq subsystem abstractions
apart from the IRQCHIP_DECLARE() macro.

Yes, I was not sure we can call it IRQCHIP hence the RFC PATCH.

Both ACLINT MSWI and SSWI are special devices providing only IPI
support so I will re-think how to fit this.

If you implemented it on top of the IPI irq_domain abstraction, making
your IPIs actual IRQs, use the proper interrupt flows and accounting,
then it would make sense to call it an irqchip driver. But as it
stands, it has no place in drivers/irqchip.

Okay, let me explore IPI irq_domain if it is suitable for this.

Regards,
Anup

Thanks,

        M.

--
Without deviation from the norm, progress is not possible.