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Subject: Re: [PATCH 7/9] irqchip: add a RISC-V PLIC driver
To:     Christoph Hellwig <hch@lst.de>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "palmer@sifive.com" <palmer@sifive.com>,
        "jason@lakedaemon.net" <jason@lakedaemon.net>,
        "marc.zyngier@arm.com" <marc.zyngier@arm.com>,
        "robh+dt@kernel.org" <robh+dt@kernel.org>,
        "mark.rutland@arm.com" <mark.rutland@arm.com>
Cc:     "anup@brainfault.org" <anup@brainfault.org>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        "aou@eecs.berkeley.edu" <aou@eecs.berkeley.edu>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-riscv@lists.infradead.org" <linux-riscv@lists.infradead.org>,
        "shorne@gmail.com" <shorne@gmail.com>
References: <20180726143723.16585-1-hch@lst.de>
 <20180726143723.16585-8-hch@lst.de>
From:   Atish Patra <atish.patra@wdc.com>
Message-ID: <1b3f6066-0c7c-a5f5-75ad-559fe81091ee@wdc.com>
Date:   Fri, 27 Jul 2018 17:04:52 -0700
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On 7/26/18 7:38 AM, Christoph Hellwig wrote:
> This patch adds a driver for the Platform Level Interrupt Controller (PLIC)
> specified as part of the RISC-V supervisor level ISA manual, in the memory
> layout implemented by SiFive and qemu.
> 
> The PLIC connects global interrupt sources to the local interrupt controller
> on each hart.
> 
> This driver is based on the driver in the RISC-V tree from Palmer Dabbelt,
> but has been almost entirely rewritten since.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

I tried to boot HighFive Unleashed with the patch series after applying 
all the patches from riscv-all branch except timer & irq patches. It 
gets stuck pretty early.

Here is my github repo with all the changes:
https://github.com/atishp04/riscv-linux/commits/master_chris_cleanup_hifive

I am still looking into it.
Palmer: Did I miss something?

FWIW, here is the boot log.
--------- Boot log -------------------------------------------
[    0.000000] RCU: Adjusting geometry for rcu_fanout_leaf=16, nr_cpu_ids=5
[    0.000000] NR_IRQS: 0, nr_irqs: 0, preallocated irqs: 0
[    0.000000] plic: mapped 53 interrupts to 4 (out of 9) handlers.
[    0.000000] clocksource: riscv_clocksource: mask: 0xffffffffffffffff 
max_cycles: 0x1d854df40, max_idle_ns: 3526361616960 ns
[    0.000000] Calibrating delay loop (skipped), value calculated using 
timer frequency.. 2.00 BogoMIPS (lpj=10000)
[    0.010000] pid_max: default: 32768 minimum: 301
[    0.010000] Mount-cache hash table entries: 16384 (order: 5, 131072 
bytes)
[    0.020000] Mountpoint-cache hash table entries: 16384 (order: 5, 
131072 bytes)
[    0.020000] Hierarchical SRCU implementation.
[    0.030000] smp: Bringing up secondary CPUs ...
> ---
>   drivers/irqchip/Kconfig          |  13 ++
>   drivers/irqchip/Makefile         |   1 +
>   drivers/irqchip/irq-riscv-plic.c | 219 +++++++++++++++++++++++++++++++
>   3 files changed, 233 insertions(+)
>   create mode 100644 drivers/irqchip/irq-riscv-plic.c
> 
> diff --git a/drivers/irqchip/Kconfig b/drivers/irqchip/Kconfig
> index e9233db16e03..5ac6dd922a0d 100644
> --- a/drivers/irqchip/Kconfig
> +++ b/drivers/irqchip/Kconfig
> @@ -372,3 +372,16 @@ config QCOM_PDC
>   	  IRQs for Qualcomm Technologies Inc (QTI) mobile chips.
>   
>   endmenu
> +
> +config RISCV_PLIC
> +	bool "Platform-Level Interrupt Controller"
> +	depends on RISCV
> +	default y
> +	help
> +	   This enables support for the PLIC chip found in standard RISC-V
> +	   systems.  The PLIC controls devices interrupts and connects them to
> +	   each core's local interrupt controller.  Aside from timer and
> +	   software interrupts, all other interrupt sources (MSI, GPIO, etc)
> +	   are subordinate to the PLIC.
> +
> +	   If you don't know what to do here, say Y.
> diff --git a/drivers/irqchip/Makefile b/drivers/irqchip/Makefile
> index 15f268f646bf..bf9238da8a31 100644
> --- a/drivers/irqchip/Makefile
> +++ b/drivers/irqchip/Makefile
> @@ -87,3 +87,4 @@ obj-$(CONFIG_MESON_IRQ_GPIO)		+= irq-meson-gpio.o
>   obj-$(CONFIG_GOLDFISH_PIC) 		+= irq-goldfish-pic.o
>   obj-$(CONFIG_NDS32)			+= irq-ativic32.o
>   obj-$(CONFIG_QCOM_PDC)			+= qcom-pdc.o
> +obj-$(CONFIG_RISCV_PLIC)		+= irq-riscv-plic.o
> diff --git a/drivers/irqchip/irq-riscv-plic.c b/drivers/irqchip/irq-riscv-plic.c
> new file mode 100644
> index 000000000000..274fe2cba544
> --- /dev/null
> +++ b/drivers/irqchip/irq-riscv-plic.c
> @@ -0,0 +1,219 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2017 SiFive
> + * Copyright (C) 2018 Christoph Hellwig
> + */
> +#define pr_fmt(fmt) "plic: " fmt
> +#include <linux/cpumask.h>
> +#include <linux/interrupt.h>
> +#include <linux/io.h>
> +#include <linux/irq.h>
> +#include <linux/irqchip.h>
> +#include <linux/irqdomain.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/of_address.h>
> +#include <linux/of_irq.h>
> +#include <linux/platform_device.h>
> +#include <linux/spinlock.h>
> +
> +/*
> + * From the RISC-V Priviledged Spec v1.10:
> + *
> + * Global interrupt sources are assigned small unsigned integer identifiers,
> + * beginning at the value 1.  An interrupt ID of 0 is reserved to mean "no
> + * interrupt".  Interrupt identifiers are also used to break ties when two or
> + * more interrupt sources have the same assigned priority. Smaller values of
> + * interrupt ID take precedence over larger values of interrupt ID.
> + *
> + * While the RISC-V supervisor spec doesn't define the maximum number of
> + * devices supported by the PLIC, the largest number supported by devices
> + * marked as 'riscv,plic0' (which is the only device type this driver supports,
> + * and is the only extant PLIC as of now) is 1024.  As mentioned above, device
> + * 0 is defined to be non-existent so this device really only supports 1023
> + * devices.
> + */
> +#define MAX_DEVICES			1024
> +#define MAX_CONTEXTS			15872
> +

Is there any way we can preserve some of the comments in the original 
patch about memory-mapped control registers or at least a reference 
where to find the register offset calculations?

IMHO, it is helpful for anybody who is not familiar with the details.
> +/*
> + * Each interrupt source has a priority register associated with it.
> + * We always hardwire it to one in Linux.
> + */
> +#define PRIORITY_BASE			0
> +#define	    PRIORITY_PER_ID		4
> +
> +/*
> + * Each hart context has a vector of interupt enable bits associated with it.
> + * There's one bit for each interrupt source.
> + */
> +#define ENABLE_BASE			0x2000
> +#define     ENABLE_PER_HART		0x80
> +
> +/*
> + * Each hart context has a set of control registers associated with it.  Right
> + * now there's only two: a source priority threshold over which the hart will
> + * take an interrupt, and a register to claim interrupts.
> + */
> +#define CONTEXT_BASE			0x200000
> +#define     CONTEXT_PER_HART		0x1000
> +#define     CONTEXT_THRESHOLD		0x00
> +#define     CONTEXT_CLAIM		0x04
> +
> +static void __iomem *plic_regs;
> +
> +static inline void __iomem *plic_hart_offset(int ctxid)
> +{
> +	return plic_regs + CONTEXT_BASE + ctxid * CONTEXT_PER_HART;
> +}
> +
> +/*
> + * Protect mask operations on the registers given that we can't assume that
> + * atomic memory operations work on them.
> + */
> +static DEFINE_SPINLOCK(plic_toggle_lock);
> +
> +static inline void plic_toggle(int ctxid, int hwirq, int enable)
> +{
> +	u32 __iomem *reg = plic_regs + ENABLE_BASE + ctxid * ENABLE_PER_HART;

shouldn't it be
u32 __iomem *reg = plic_regs + ENABLE_BASE + ctxid * ENABLE_PER_HART + 
(hwirq / 32) * 4;

Without that change, plic_handle_irq() gets called before irq mapping as 
plic was not disabled for that irq.

As per comment in the original patch,
--------------------------------------------------------------
* base + 0x002000: Enable bits for sources 0-31 on context 0
* base + 0x002004: Enable bits for sources 32-63 on context 0
--------------------------------------------------------------

> +	u32 hwirq_mask = 1 << (hwirq % 32);
> +
> +	spin_lock(&plic_toggle_lock);
> +	if (enable)
> +		writel(readl(reg) | hwirq_mask, reg);
> +	else
> +		writel(readl(reg) & ~hwirq_mask, reg);
> +	spin_unlock(&plic_toggle_lock);
> +}
> +
> +static inline void plic_irq_toggle(struct irq_data *d, int enable)
> +{
> +	int cpu;
> +
> +	writel(enable, plic_regs + PRIORITY_BASE + d->hwirq * PRIORITY_PER_ID);
> +	for_each_present_cpu(cpu)
> +		plic_toggle(cpu, d->hwirq, enable);
> +}
> +
> +static void plic_irq_enable(struct irq_data *d)
> +{
> +	plic_irq_toggle(d, 1);
> +}
> +
> +static void plic_irq_disable(struct irq_data *d)
> +{
> +	plic_irq_toggle(d, 0);
> +}
> +
> +static struct irq_chip plic_chip = {
> +	.name		= "riscv,plic0",
> +	/*
> +	 * There is no need to mask/unmask PLIC interrupts.  They are "masked"
> +	 * by reading claim and "unmasked" when writing it back.
> +	 */
> +	.irq_enable	= plic_irq_enable,
> +	.irq_disable	= plic_irq_disable,
> +};
> +
> +static int plic_irqdomain_map(struct irq_domain *d, unsigned int irq,
> +			      irq_hw_number_t hwirq)
> +{
> +	irq_set_chip_and_handler(irq, &plic_chip, handle_simple_irq);
> +	irq_set_chip_data(irq, NULL);
> +	irq_set_noprobe(irq);
> +	return 0;
> +}
> +
> +static const struct irq_domain_ops plic_irqdomain_ops = {
> +	.map		= plic_irqdomain_map,
> +	.xlate		= irq_domain_xlate_onecell,
> +};
> +
> +static struct irq_domain *plic_irqdomain;
> +
> +/*
> + * Handling an interrupt is a two-step process: first you claim the interrupt
> + * by reading the claim register, then you complete the interrupt by writing
> + * that source ID back to the same claim register.  This automatically enables
> + * and disables the interrupt, so there's nothing else to do.
> + */
> +static void plic_handle_irq(struct pt_regs *regs)
> +{
> +	void __iomem *claim =
> +		plic_hart_offset(smp_processor_id()) + CONTEXT_CLAIM;
> +	irq_hw_number_t hwirq;
> +
> +	csr_clear(sie, SIE_STIE);
> +	while ((hwirq = readl(claim))) {
> +		int irq = irq_find_mapping(plic_irqdomain, hwirq);
> +
> +		if (unlikely(irq <= 0)) {
> +			pr_warn_ratelimited("can't find mapping for hwirq %lu\n",
> +					hwirq);

Ratlimiting the warning message here didn't help as ack_bad_irq() still 
print message still flooded the console without any useful info.

Regards,
Atish
> +			ack_bad_irq(irq);
> +		} else {
> +			generic_handle_irq(irq);
> +		}
> +		writel(hwirq, claim);
> +	}
> +	csr_set(sie, SIE_STIE);
> +}
> +
> +static int __init plic_init(struct device_node *node,
> +		struct device_node *parent)
> +{
> +	int error = 0, nr_mapped = 0, nr_handlers, cpu;
> +	u32 nr_irqs;
> +
> +	if (plic_regs) {
> +		pr_warning("PLIC already present.\n");
> +		return -ENXIO;
> +	}
> +
> +	plic_regs = of_iomap(node, 0);
> +	if (WARN_ON(!plic_regs))
> +		return -EIO;
> +
> +	error = -EINVAL;
> +	of_property_read_u32(node, "riscv,ndev", &nr_irqs);
> +	if (WARN_ON(!nr_irqs))
> +		goto out_iounmap;
> +
> +	nr_handlers = of_irq_count(node);
> +	if (WARN_ON(!nr_handlers))
> +		goto out_iounmap;
> +	if (WARN_ON(nr_handlers < num_possible_cpus()))
> +		goto out_iounmap;
> +
> +	error = -ENOMEM;
> +	plic_irqdomain = irq_domain_add_linear(node, nr_irqs + 1,
> +			&plic_irqdomain_ops, NULL);
> +	if (WARN_ON(!plic_irqdomain))
> +		goto out_iounmap;
> +
> +	/*
> +	 * We assume that each present hart is wire up to the PLIC.
> +	 * If that isn't the case in the future this code will need to be
> +	 * modified.
> +	 */
> +	for_each_present_cpu(cpu) {
> +		irq_hw_number_t hwirq;
> +
> +		/* priority must be > threshold to trigger an interrupt */
> +		writel(0, plic_hart_offset(cpu) + CONTEXT_THRESHOLD);
> +		for (hwirq = 1; hwirq <= nr_irqs; ++hwirq)
> +			plic_toggle(cpu, hwirq, 0);
> +		nr_mapped++;
> +	}
> +
> +	pr_info("mapped %d interrupts to %d (out of %d) handlers.\n",
> +		nr_irqs, nr_mapped, nr_handlers);
> +	set_handle_irq(plic_handle_irq);
> +	return 0;
> +
> +out_iounmap:
> +	iounmap(plic_regs);
> +	return error;
> +}
> +
> +IRQCHIP_DECLARE(plic0, "riscv,plic0", plic_init);
>