Re: [PATCH v4 21/26] irqchip/gic-v5: Add GICv5 IRS/SPI support

Jonathan Cameron
2025-05-28T16:29:00Z

On Tue, 13 May 2025 19:48:14 +0200
Lorenzo Pieralisi <lpieralisi@kernel.org> wrote:

> The GICv5 Interrupt Routing Service (IRS) component implements
> interrupt management and routing in the GICv5 architecture.
>
> A GICv5 system comprises one or more IRSes, that together
> handle the interrupt routing and state for the system.
>
> An IRS supports Shared Peripheral Interrupts (SPIs), that are
> interrupt sources directly connected to the IRS; they do not
> rely on memory for storage. The number of supported SPIs is
> fixed for a given implementation and can be probed through IRS
> IDR registers.
>
> SPI interrupt state and routing are managed through GICv5
> instructions.
>
> Each core (PE in GICv5 terms) in a GICv5 system is identified with
> an Interrupt AFFinity ID (IAFFID).
>
> An IRS manages a set of cores that are connected to it.
>
> Firmware provides a topology description that the driver uses
> to detect to which IRS a CPU (ie an IAFFID) is associated with.
>
> Use probeable information and firmware description to initialize
> the IRSes and implement GICv5 IRS SPIs support through an
> SPI-specific IRQ domain.
>
> The GICv5 IRS driver:
>
> - Probes IRSes in the system to detect SPI ranges
> - Associates an IRS with a set of cores connected to it
> - Adds an IRQchip structure for SPI handling
>
> SPIs priority is set to a value corresponding to the lowest
> permissible priority in the system (taking into account the
> implemented priority bits of the IRS and CPU interface).
>
> Since all IRQs are set to the same priority value, the value
> itself does not matter as long as it is a valid one.
>
> Co-developed-by: Sascha Bischoff <sascha.bischoff@arm.com>
> Signed-off-by: Sascha Bischoff <sascha.bischoff@arm.com>
> Co-developed-by: Timothy Hayes <timothy.hayes@arm.com>
> Signed-off-by: Timothy Hayes <timothy.hayes@arm.com>
> Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
> Cc: Will Deacon <will@kernel.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Marc Zyngier <maz@kernel.org>

A few comments inline. Mostly around of cpu phandle parsing.
+CC Ali as there is a comment on his SMT DT patch set inline.

> ---
> arch/arm64/include/asm/sysreg.h | 36 +++
> drivers/irqchip/Makefile | 2 +-
> drivers/irqchip/irq-gic-v5-irs.c | 433 +++++++++++++++++++++++++++++++++++++
> drivers/irqchip/irq-gic-v5.c | 341 +++++++++++++++++++++++++++--
> include/linux/irqchip/arm-gic-v5.h | 130 +++++++++++
> 5 files changed, 920 insertions(+), 22 deletions(-)
>
> diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
> index 9d28d408f9c6df24526dd8ecbf3c7d920246b22d..fbac3b6f056ae6fafd64457600d45808e4904ae3 100644
> --- a/arch/arm64/include/asm/sysreg.h
> +++ b/arch/arm64/include/asm/sysreg.h
> @@ -1082,14 +1082,50 @@
> /*
> * Definitions for GICv5 instructions
> */

>
> +/* Shift and mask definitions for GIC CDAFF */

Similar comment. Mask definitions seems more accurate to me.

> +/* Shift and mask definitions for GIC CDDIS */
> +#define GICV5_GIC_CDDIS_TYPE_MASK GENMASK_ULL(31, 29)
> +#define GICV5_GIC_CDDIS_TYPE(r) FIELD_GET(GICV5_GIC_CDDIS_TYPE_MASK, r)
> +#define GICV5_GIC_CDDIS_ID_MASK GENMASK_ULL(23, 0)
> +#define GICV5_GIC_CDDIS_ID(r) FIELD_GET(GICV5_GIC_CDDIS_ID_MASK, r)

Similar to earlier comment. I'm not sure the shortened forms are worth the bother.

> diff --git a/drivers/irqchip/irq-gic-v5-irs.c b/drivers/irqchip/irq-gic-v5-irs.c
> new file mode 100644
> index 0000000000000000000000000000000000000000..8c448487b909c7d3b4e1f95a5bc02b741ecc40b3
> --- /dev/null
> +++ b/drivers/irqchip/irq-gic-v5-irs.c
> @@ -0,0 +1,433 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (C) 2024-2025 ARM Limited, All Rights Reserved.
> + */
> +
> +#define pr_fmt(fmt) "GICv5 IRS: " fmt
> +
> +#include <linux/of.h>
> +#include <linux/of_address.h>
> +
> +#include <linux/irqchip.h>
> +#include <linux/irqchip/arm-gic-v5.h>

> +int gicv5_spi_irq_set_type(struct irq_data *d, unsigned int type)
> +{
> + struct gicv5_irs_chip_data *irs_data = d->chip_data;
> + u32 selr, cfgr;
> + bool level;
> + int ret;
> +
> + switch (type) {
> + case IRQ_TYPE_EDGE_RISING:
> + case IRQ_TYPE_EDGE_FALLING:
> + level = false;
> + break;
> + case IRQ_TYPE_LEVEL_HIGH:
> + case IRQ_TYPE_LEVEL_LOW:
> + level = true;
> + break;
> + default:
> + return -EINVAL;
> + }
> +
> + guard(raw_spinlock)(&irs_data->spi_config_lock);
> +
> + selr = FIELD_PREP(GICV5_IRS_SPI_SELR_ID, d->hwirq);
> + irs_writel_relaxed(irs_data, selr, GICV5_IRS_SPI_SELR);
> + ret = gicv5_irs_wait_for_spi_op(irs_data);
> + if (ret)
> + return ret;
> +
> + cfgr = FIELD_PREP(GICV5_IRS_SPI_CFGR_TM, level);
> +
> + irs_writel_relaxed(irs_data, cfgr, GICV5_IRS_SPI_CFGR);
> + ret = gicv5_irs_wait_for_spi_op(irs_data);
> + if (ret)
> + return ret;
> +
> + return 0;
return gicv5_irq_wait_for_spi_op()

unless more code turns up here in a later patch.

> +}

> +
> +static void __init gicv5_irs_init_bases(struct gicv5_irs_chip_data *irs_data,
> + void __iomem *irs_base,
> + struct fwnode_handle *handle)
> +{
> + struct device_node *np = to_of_node(handle);
> + u32 cr0, cr1;
> +
> + irs_data->fwnode = handle;
> + irs_data->irs_base = irs_base;
> +
> + if (of_property_read_bool(np, "dma-noncoherent")) {
> + /*
> + * A non-coherent IRS implies that some cache levels cannot be
> + * used coherently by the cores and GIC. Our only option is to mark
> + * memory attributes for the GIC as non-cacheable; by default,
> + * non-cacheable memory attributes imply outer-shareable
> + * shareability, the value written into IRS_CR1_SH is ignored.
> + */
> + cr1 = FIELD_PREP(GICV5_IRS_CR1_VPED_WA, GICV5_NO_WRITE_ALLOC) |
As per earlier comments is this less clear as:
cr1 = FIELD_PREP(GICV5_IRS_CR1_VPED_WA, 0) |

To me, seems fine but up to you.

> + FIELD_PREP(GICV5_IRS_CR1_VPED_RA, GICV5_NO_READ_ALLOC) |
> + FIELD_PREP(GICV5_IRS_CR1_VMD_WA, GICV5_NO_WRITE_ALLOC) |
> + FIELD_PREP(GICV5_IRS_CR1_VMD_RA, GICV5_NO_READ_ALLOC) |
> + FIELD_PREP(GICV5_IRS_CR1_VPET_RA, GICV5_NO_READ_ALLOC) |
> + FIELD_PREP(GICV5_IRS_CR1_VMT_RA, GICV5_NO_READ_ALLOC) |
> + FIELD_PREP(GICV5_IRS_CR1_IST_WA, GICV5_NO_WRITE_ALLOC) |
> + FIELD_PREP(GICV5_IRS_CR1_IST_RA, GICV5_NO_READ_ALLOC) |
> + FIELD_PREP(GICV5_IRS_CR1_IC, GICV5_NON_CACHE) |
> + FIELD_PREP(GICV5_IRS_CR1_OC, GICV5_NON_CACHE);
> + irs_data->flags |= IRS_FLAGS_NON_COHERENT;
> + } else {
> + cr1 = FIELD_PREP(GICV5_IRS_CR1_VPED_WA, GICV5_WRITE_ALLOC) |
> + FIELD_PREP(GICV5_IRS_CR1_VPED_RA, GICV5_READ_ALLOC) |
> + FIELD_PREP(GICV5_IRS_CR1_VMD_WA, GICV5_WRITE_ALLOC) |
> + FIELD_PREP(GICV5_IRS_CR1_VMD_RA, GICV5_READ_ALLOC) |
> + FIELD_PREP(GICV5_IRS_CR1_VPET_RA, GICV5_READ_ALLOC) |
> + FIELD_PREP(GICV5_IRS_CR1_VMT_RA, GICV5_READ_ALLOC) |
> + FIELD_PREP(GICV5_IRS_CR1_IST_WA, GICV5_WRITE_ALLOC) |
> + FIELD_PREP(GICV5_IRS_CR1_IST_RA, GICV5_READ_ALLOC) |
> + FIELD_PREP(GICV5_IRS_CR1_IC, GICV5_WB_CACHE) |
> + FIELD_PREP(GICV5_IRS_CR1_OC, GICV5_WB_CACHE) |
> + FIELD_PREP(GICV5_IRS_CR1_SH, GICV5_INNER_SHARE);
> + }
> +
> + irs_writel_relaxed(irs_data, cr1, GICV5_IRS_CR1);
> +
> + cr0 = FIELD_PREP(GICV5_IRS_CR0_IRSEN, 0x1);
> + irs_writel_relaxed(irs_data, cr0, GICV5_IRS_CR0);
> + gicv5_irs_wait_for_idle(irs_data);
> +}
> +
> +static int __init gicv5_irs_of_init_affinity(struct device_node *node,
> + struct gicv5_irs_chip_data *irs_data,
> + u8 iaffid_bits)
> +{
> + /*
> + * Detect IAFFID<->CPU mappings from the device tree and
> + * record IRS<->CPU topology information.
> + */
> + u16 iaffid_mask = GENMASK(iaffid_bits - 1, 0);
> + u16 *iaffids __free(kfree) = NULL;

See comments in cleanup.h. Linus has been fairly clear he doesn't like
separating the constructor and destructor like this - just declare
iaffids where you construct it.

> + int ret, i, ncpus, niaffids;
> +

> + ncpus = of_property_count_elems_of_size(node, "cpus", sizeof(u32));

cpus is a phandle? I think this is going to run into current discussion
on what phandles to CPUs on an SMT system look like (Rob Herring and Mark
Rutland have different views)
https://lore.kernel.org/linux-arm-kernel/20250512080715.82-1-alireza.sanaee@huawei.com/

Anyhow this doesn't look right to me.
I think it should be of_count_phandle_with_args() Potentially with cpu-cells
as the argument depending on how that thread goes.

> + if (ncpus < 0)
> + return -EINVAL;
> +
> + niaffids = of_property_count_elems_of_size(node, "arm,iaffids",
> + sizeof(u16));
> + if (niaffids != ncpus)
> + return -EINVAL;
> +
u16 *iaffids __free(kfree) = kcalloc(niaffids, sizeof(*iaffids),
GFP_KERNEL);

> + iaffids = kcalloc(niaffids, sizeof(*iaffids), GFP_KERNEL);
> + if (!iaffids)
> + return -ENOMEM;
> +
> + ret = of_property_read_u16_array(node, "arm,iaffids", iaffids, niaffids);
> + if (ret)
> + return ret;
> +
> + for (i = 0; i < ncpus; i++) {
> + struct device_node *cpu_node;
> + u32 cpu_phandle;
> + int cpu;
> +
> + if (of_property_read_u32_index(node, "cpus", i, &cpu_phandle))
> + continue;
> +
> + cpu_node = of_find_node_by_phandle(cpu_phandle);

cpu_node = of_parse_phandle(node, "cpus", i);

not work here?

> + if (WARN_ON(!cpu_node))
> + continue;
> +
> + cpu = of_cpu_node_to_id(cpu_node);

If this is all you want then Ali's series gives you a helper

cpu = of_cpu_phandle_to_id(node, &cpu_node, i);

Though even better to have a helper that allows
cpu = of_cpu_phandle_to_id(node, NULL, i); and handles
the node put as internally.

Ali, any reason we can't do that? Seems to be a fairly common
pattern.

> + of_node_put(cpu_node);
> + if (WARN_ON(cpu < 0))
> + continue;
> +
> + if (iaffids[i] & ~iaffid_mask) {
> + pr_warn("CPU %d iaffid 0x%x exceeds IRS iaffid bits\n",
> + cpu, iaffids[i]);
> + continue;
> + }
> +
> + per_cpu(cpu_iaffid, cpu).iaffid = iaffids[i];
> + per_cpu(cpu_iaffid, cpu).valid = true;
> +
> + /* We also know that the CPU is connected to this IRS */
> + per_cpu(per_cpu_irs_data, cpu) = irs_data;
> + }
> +
> + return ret;
> +}

> diff --git a/drivers/irqchip/irq-gic-v5.c b/drivers/irqchip/irq-gic-v5.c
> index a50982e5d98816d88e4fca37cc0ac31684fb6c76..e58ff345dbfaf840b17ad63c4fdb6c227137cf4b 100644
> --- a/drivers/irqchip/irq-gic-v5.c
> +++ b/drivers/irqchip/irq-gic-v5.c
>
> +
> +static int gicv5_spi_irq_set_irqchip_state(struct irq_data *d,
> + enum irqchip_irq_state which,
> + bool val)
> +{

Similar to previous, I'd call the state parameter state rather than val.

> diff --git a/include/linux/irqchip/arm-gic-v5.h b/include/linux/irqchip/arm-gic-v5.h
> index 4ff0ba64d9840c3844671f7850bb3d81ba2eb1b6..187af307de9170d9569898cb1e50de376a38bd0a 100644
> --- a/include/linux/irqchip/arm-gic-v5.h
> +++ b/include/linux/irqchip/arm-gic-v5.h
> @@ -5,6 +5,8 @@
> #ifndef __LINUX_IRQCHIP_ARM_GIC_V5_H
> #define __LINUX_IRQCHIP_ARM_GIC_V5_H

>
> +#define GICV5_NO_READ_ALLOC 0b0
> +#define GICV5_READ_ALLOC 0b1
> +#define GICV5_NO_WRITE_ALLOC 0b0
> +#define GICV5_WRITE_ALLOC 0b1

Given these are being written to fields called _RA and _WA
so the defines provide value over 0 and 1 in appropriate places?
Maybe just about. Anyhow, your code so on this up to you.

> +
> +#define GICV5_NON_CACHE 0b00
> +#define GICV5_WB_CACHE 0b01
> +#define GICV5_WT_CACHE 0b10
> +
> +#define GICV5_NON_SHARE 0b00
> +#define GICV5_OUTER_SHARE 0b10
> +#define GICV5_INNER_SHARE 0b11
> +
> +#define GICV5_IRS_IDR1 0x0004
> +#define GICV5_IRS_IDR2 0x0008
> +#define GICV5_IRS_IDR5 0x0014
> +#define GICV5_IRS_IDR6 0x0018
> +#define GICV5_IRS_IDR7 0x001c
> +#define GICV5_IRS_CR0 0x0080
> +#define GICV5_IRS_CR1 0x0084
> +#define GICV5_IRS_SPI_SELR 0x0108
> +#define GICV5_IRS_SPI_CFGR 0x0114
> +#define GICV5_IRS_SPI_STATUSR 0x0118
> +#define GICV5_IRS_PE_SELR 0x0140
> +#define GICV5_IRS_PE_STATUSR 0x0144
> +#define GICV5_IRS_PE_CR0 0x0148

Blank line here as this is end of register offsets.

> +#define GICV5_IRS_IDR1_PRIORITY_BITS GENMASK(22, 20)
> +#define GICV5_IRS_IDR1_IAFFID_BITS GENMASK(19, 16)