Re: [PATCH v2 2/3] irqchip: add T-HEAD C900 ACLINT SSWI driver

[Samuel Holland]

Hi Inochi,

On 2024-10-09 5:44 PM, Inochi Amaoto wrote:
> Add a driver for the T-HEAD C900 ACLINT SSWI device, which is an
> enhanced implementation of the RISC-V ACLINT SSWI specification.
> This device allows the system to send ipi via fast device interface.
> 
> Signed-off-by: Inochi Amaoto <inochiama@xxxxxxxxx>
> ---
>  drivers/irqchip/Kconfig                      |  10 ++
>  drivers/irqchip/Makefile                     |   1 +
>  drivers/irqchip/irq-thead-c900-aclint-sswi.c | 166 +++++++++++++++++++
>  include/linux/cpuhotplug.h                   |   1 +
>  4 files changed, 178 insertions(+)
>  create mode 100644 drivers/irqchip/irq-thead-c900-aclint-sswi.c
> 
> diff --git a/drivers/irqchip/Kconfig b/drivers/irqchip/Kconfig
> index 341cd9ca5a05..32671385cbb7 100644
> --- a/drivers/irqchip/Kconfig
> +++ b/drivers/irqchip/Kconfig
> @@ -611,6 +611,16 @@ config STARFIVE_JH8100_INTC
>  
>  	  If you don't know what to do here, say Y.
>  
> +config THEAD_C900_ACLINT_SSWI
> +	bool "THEAD C9XX ACLINT S-mode IPI Interrupt Controller"
> +	depends on RISCV
> +	select IRQ_DOMAIN_HIERARCHY
> +	help
> +	  This enables support for T-HEAD specific ACLINT SSWI device
> +	  support.
> +
> +	  If you don't know what to do here, say Y.
> +
>  config EXYNOS_IRQ_COMBINER
>  	bool "Samsung Exynos IRQ combiner support" if COMPILE_TEST
>  	depends on (ARCH_EXYNOS && ARM) || COMPILE_TEST
> diff --git a/drivers/irqchip/Makefile b/drivers/irqchip/Makefile
> index e3679ec2b9f7..583418261253 100644
> --- a/drivers/irqchip/Makefile
> +++ b/drivers/irqchip/Makefile
> @@ -101,6 +101,7 @@ obj-$(CONFIG_RISCV_APLIC_MSI)		+= irq-riscv-aplic-msi.o
>  obj-$(CONFIG_RISCV_IMSIC)		+= irq-riscv-imsic-state.o irq-riscv-imsic-early.o irq-riscv-imsic-platform.o
>  obj-$(CONFIG_SIFIVE_PLIC)		+= irq-sifive-plic.o
>  obj-$(CONFIG_STARFIVE_JH8100_INTC)	+= irq-starfive-jh8100-intc.o
> +obj-$(CONFIG_THEAD_C900_ACLINT_SSWI)	+= irq-thead-c900-aclint-sswi.o
>  obj-$(CONFIG_IMX_IRQSTEER)		+= irq-imx-irqsteer.o
>  obj-$(CONFIG_IMX_INTMUX)		+= irq-imx-intmux.o
>  obj-$(CONFIG_IMX_MU_MSI)		+= irq-imx-mu-msi.o
> diff --git a/drivers/irqchip/irq-thead-c900-aclint-sswi.c b/drivers/irqchip/irq-thead-c900-aclint-sswi.c
> new file mode 100644
> index 000000000000..b96d3b81dc14
> --- /dev/null
> +++ b/drivers/irqchip/irq-thead-c900-aclint-sswi.c
> @@ -0,0 +1,166 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2024 Inochi Amaoto <inochiama@xxxxxxxxx>
> + */
> +
> +#define pr_fmt(fmt) "thead-c900-aclint-sswi: " fmt
> +#include <linux/cpu.h>
> +#include <linux/interrupt.h>
> +#include <linux/io.h>
> +#include <linux/irq.h>
> +#include <linux/irqchip.h>
> +#include <linux/irqchip/chained_irq.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/of_address.h>
> +#include <linux/of_irq.h>
> +#include <linux/pci.h>
> +#include <linux/spinlock.h>
> +#include <linux/smp.h>
> +#include <linux/string_choices.h>
> +
> +#define ACLINT_xSWI_REGISTER_SIZE	4
> +
> +static int sswi_ipi_virq __ro_after_init;
> +static DEFINE_PER_CPU(void __iomem *, sswi_cpu_regs);
> +
> +static void thead_aclint_sswi_ipi_send(unsigned int cpu)
> +{
> +	writel_relaxed(0x1, per_cpu(sswi_cpu_regs, cpu));
> +}
> +
> +static void thead_aclint_sswi_ipi_clear(void)
> +{
> +	writel_relaxed(0x0, this_cpu_read(sswi_cpu_regs));

This isn't quite compliant with the ACLINT spec[1], which states: "Writing 0 to
the least significant bit of a SETSSIP register has no effect". In a RISC-V
ACLINT, only the CSR write is required to clear the interrupt.

This implementation does match the behavior of the T-HEAD CLINT extensions which
are also present in C906/C910[2][3][4].

This raises the question: in the older CPUs, using this functionality requires
setting the mxstatus.CLINTEE bit from M-mode. Is this still the case for the
C920 CPU in SG2044? If so, the driver should check sxstatus.CLINTEE when probing.

It would also be ideal if we could support the other SoCs that use this same IP
block, but with the other CLINT binding.

Regards,
Samuel

[1]: https://github.com/riscv/riscv-aclint/blob/main/riscv-aclint.adoc
[2]:
https://occ-intl-prod.oss-ap-southeast-1.aliyuncs.com/resource/XuanTie-OpenC906-UserManual.pdf
[3]:
https://github.com/XUANTIE-RV/openc906/blob/main/C906_RTL_FACTORY/gen_rtl/clint/rtl/clint_func.v#L285
[4]:
https://github.com/XUANTIE-RV/openc906/blob/main/C906_RTL_FACTORY/gen_rtl/cp0/rtl/aq_cp0_trap_csr.v#L1240

> +}
> +
> +static void thead_aclint_sswi_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);
> +	thead_aclint_sswi_ipi_clear();
> +
> +	ipi_mux_process();
> +
> +	chained_irq_exit(chip, desc);
> +}
> +
> +static int thead_aclint_sswi_starting_cpu(unsigned int cpu)
> +{
> +	enable_percpu_irq(sswi_ipi_virq, irq_get_trigger_type(sswi_ipi_virq));
> +
> +	return 0;
> +}
> +
> +static int thead_aclint_sswi_dying_cpu(unsigned int cpu)
> +{
> +	thead_aclint_sswi_ipi_clear();
> +
> +	disable_percpu_irq(sswi_ipi_virq);
> +
> +	return 0;
> +}
> +
> +static int __init aclint_sswi_parse_irq(struct fwnode_handle *fwnode,
> +					void __iomem *reg)
> +{
> +	struct of_phandle_args parent;
> +	unsigned long hartid;
> +	u32 contexts, i;
> +	int rc, cpu;
> +
> +	contexts = of_irq_count(to_of_node(fwnode));
> +	if (!(contexts)) {
> +		pr_err("%pfwP: no ACLINT SSWI context available\n", fwnode);
> +		return -EINVAL;
> +	}
> +
> +	for (i = 0; i < contexts; i++) {
> +		rc = of_irq_parse_one(to_of_node(fwnode), i, &parent);
> +		if (rc)
> +			return rc;
> +
> +		rc = riscv_of_parent_hartid(parent.np, &hartid);
> +		if (rc)
> +			return rc;
> +
> +		if (parent.args[0] != RV_IRQ_SOFT)
> +			return -ENOTSUPP;
> +
> +		cpu = riscv_hartid_to_cpuid(hartid);
> +
> +		per_cpu(sswi_cpu_regs, cpu) = reg + i * ACLINT_xSWI_REGISTER_SIZE;
> +	}
> +
> +	pr_info("%pfwP: register %u CPU%s\n", fwnode, contexts, str_plural(contexts));
> +
> +	return 0;
> +}
> +
> +static int __init aclint_sswi_probe(struct fwnode_handle *fwnode)
> +{
> +	struct irq_domain *domain;
> +	void __iomem *reg;
> +	int virq, rc;
> +
> +	if (!is_of_node(fwnode))
> +		return -EINVAL;
> +
> +	reg = of_iomap(to_of_node(fwnode), 0);
> +	if (!reg)
> +		return -ENOMEM;
> +
> +	/* Parse SSWI setting */
> +	rc = aclint_sswi_parse_irq(fwnode, reg);
> +	if (rc < 0)
> +		return rc;
> +
> +	/* If mulitple SSWI devices are present, do not register irq again */
> +	if (sswi_ipi_virq)
> +		return 0;
> +
> +	/* Find riscv intc domain and create IPI irq mapping */
> +	domain = irq_find_matching_fwnode(riscv_get_intc_hwnode(), DOMAIN_BUS_ANY);
> +	if (!domain) {
> +		pr_err("%pfwP: Failed to find INTC domain\n", fwnode);
> +		return -ENOENT;
> +	}
> +
> +	sswi_ipi_virq = irq_create_mapping(domain, RV_IRQ_SOFT);
> +	if (!sswi_ipi_virq) {
> +		pr_err("unable to create ACLINT SSWI IRQ mapping\n");
> +		return -ENOMEM;
> +	}
> +
> +	/* Register SSWI irq and handler */
> +	virq = ipi_mux_create(BITS_PER_BYTE, thead_aclint_sswi_ipi_send);
> +	if (virq <= 0) {
> +		pr_err("unable to create muxed IPIs\n");
> +		irq_dispose_mapping(sswi_ipi_virq);
> +		return virq < 0 ? virq : -ENOMEM;
> +	}
> +
> +	irq_set_chained_handler(sswi_ipi_virq, thead_aclint_sswi_ipi_handle);
> +
> +	cpuhp_setup_state(CPUHP_AP_IRQ_THEAD_ACLINT_SSWI_STARTING,
> +			  "irqchip/thead-aclint-sswi:starting",
> +			  thead_aclint_sswi_starting_cpu,
> +			  thead_aclint_sswi_dying_cpu);
> +
> +	riscv_ipi_set_virq_range(virq, BITS_PER_BYTE);
> +
> +	/* Announce that SSWI is providing IPIs */
> +	pr_info("providing IPIs using THEAD ACLINT SSWI\n");
> +
> +	return 0;
> +}
> +
> +static int __init aclint_sswi_early_probe(struct device_node *node,
> +					  struct device_node *parent)
> +{
> +	return aclint_sswi_probe(&node->fwnode);
> +}
> +IRQCHIP_DECLARE(thead_aclint_sswi, "thead,c900-aclint-sswi", aclint_sswi_early_probe);
> diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
> index 2361ed4d2b15..799052249c7b 100644
> --- a/include/linux/cpuhotplug.h
> +++ b/include/linux/cpuhotplug.h
> @@ -147,6 +147,7 @@ enum cpuhp_state {
>  	CPUHP_AP_IRQ_EIOINTC_STARTING,
>  	CPUHP_AP_IRQ_AVECINTC_STARTING,
>  	CPUHP_AP_IRQ_SIFIVE_PLIC_STARTING,
> +	CPUHP_AP_IRQ_THEAD_ACLINT_SSWI_STARTING,
>  	CPUHP_AP_IRQ_RISCV_IMSIC_STARTING,
>  	CPUHP_AP_IRQ_RISCV_SBI_IPI_STARTING,
>  	CPUHP_AP_ARM_MVEBU_COHERENCY,