Re: [PATCH v2] irqchip/gicv3: Add support for Range Selector (RS) feature

From: Marc Zyngier
Date: Thu Oct 05 2017 - 06:44:01 EST

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On 20/09/17 04:21, Shanker Donthineni wrote:
> A new feature Range Selector (RS) has been added to GIC specification
> in order to support more than 16 CPUs at affinity level 0. New fields
> are introduced in SGI system registers (ICC_SGI0R_EL1, ICC_SGI1R_EL1
> and ICC_ASGI1R_EL1) to relax an artificial limit of 16 at level 0.
>
> - A new RSS field in ICC_CTLR_EL3, ICC_CTLR_EL1 and ICV_CTLR_EL1:
> [18] - Range Selector Support (RSS)
> 0b0 = Targeted SGIs with affinity level 0 values of 0-15 are supported.
> 0b1 = Targeted SGIs with affinity level 0 values of 0-255 are supported.
>
> - A new RS field in ICC_SGI0R_EL1, ICC_SGI1R_EL1 and ICC_ASGI1R_EL1:
> [47:44] - RangeSelector (RS) which group of 16 TargetList[n] field
> TargetList[n] represents aff0 value ((RS*16)+n)
> When ICC_CTLR_EL3.RSS==0 or ICC_CTLR_EL1.RSS==0, RS is RES0.
>
> - A new RSS field in GICD_TYPER:
> [26] - Range Selector Support (RSS)
> 0b0 = Targeted SGIs with affinity level 0 values of 0-15 are supported.
> 0b1 = Targeted SGIs with affinity level 0 values of 0-255 are supported.
>
> Signed-off-by: Shanker Donthineni <shankerd@xxxxxxxxxxxxxx>
> ---
> Changes since v1:
> - Addrssed Marc's review comments on RSS validation checks.
> - Apply code changes to gic_compute_target_list() to support RSS feature.
> - Fix the compilation on ARM32.
>
> arch/arm/include/asm/arch_gicv3.h | 5 ++++
> arch/arm64/include/asm/arch_gicv3.h | 5 ++++
> drivers/irqchip/irq-gic-v3.c | 60 +++++++++++++++++++++++++++++++------
> include/linux/irqchip/arm-gic-v3.h | 4 +++
> 4 files changed, 65 insertions(+), 9 deletions(-)
>
> diff --git a/arch/arm/include/asm/arch_gicv3.h b/arch/arm/include/asm/arch_gicv3.h
> index 2747590..4a3b3c2 100644
> --- a/arch/arm/include/asm/arch_gicv3.h
> +++ b/arch/arm/include/asm/arch_gicv3.h
> @@ -196,6 +196,11 @@ static inline void gic_write_ctlr(u32 val)
> isb();
> }
>
> +static inline u32 gic_read_ctlr(void)
> +{
> + return read_sysreg(ICC_CTLR);
> +}
> +
> static inline void gic_write_grpen1(u32 val)
> {
> write_sysreg(val, ICC_IGRPEN1);
> diff --git a/arch/arm64/include/asm/arch_gicv3.h b/arch/arm64/include/asm/arch_gicv3.h
> index 8cef47f..aa2c795 100644
> --- a/arch/arm64/include/asm/arch_gicv3.h
> +++ b/arch/arm64/include/asm/arch_gicv3.h
> @@ -87,6 +87,11 @@ static inline void gic_write_ctlr(u32 val)
> isb();
> }
>
> +static inline u32 gic_read_ctlr(void)
> +{
> + return read_sysreg_s(SYS_ICC_CTLR_EL1);
> +}
> +
> static inline void gic_write_grpen1(u32 val)
> {
> write_sysreg_s(val, SYS_ICC_IGRPEN1_EL1);
> diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
> index 984c3ec..2d56f2b 100644
> --- a/drivers/irqchip/irq-gic-v3.c
> +++ b/drivers/irqchip/irq-gic-v3.c
> @@ -55,6 +55,7 @@ struct gic_chip_data {
> struct irq_domain *domain;
> u64 redist_stride;
> u32 nr_redist_regions;
> + bool has_rss;
> unsigned int irq_nr;
> struct partition_desc *ppi_descs[16];
> };
> @@ -63,7 +64,9 @@ struct gic_chip_data {
> static struct static_key supports_deactivate = STATIC_KEY_INIT_TRUE;
>
> static struct gic_kvm_info gic_v3_kvm_info;
> +static DEFINE_PER_CPU(bool, has_rss);
>
> +#define MPIDR_RS(mpidr) (((mpidr) & 0xF0UL) >> 4)
> #define gic_data_rdist() (this_cpu_ptr(gic_data.rdists.rdist))
> #define gic_data_rdist_rd_base() (gic_data_rdist()->rd_base)
> #define gic_data_rdist_sgi_base() (gic_data_rdist_rd_base() + SZ_64K)
> @@ -483,6 +486,10 @@ static int gic_populate_rdist(void)
>
> static void gic_cpu_sys_reg_init(void)
> {
> + int i, cpu = smp_processor_id();
> + u64 mpidr = cpu_logical_map(cpu);
> + bool need_rss = false;
> +
> /*
> * Need to check that the SRE bit has actually been set. If
> * not, it means that SRE is disabled at EL2. We're going to
> @@ -514,6 +521,40 @@ static void gic_cpu_sys_reg_init(void)
>
> /* ... and let's hit the road... */
> gic_write_grpen1(1);
> +
> + /* Keep the RSS capability status in per_cpu variable */
> + per_cpu(has_rss, cpu) = !!(gic_read_ctlr() & ICC_CTLR_EL1_RSS);
> +
> + /* Check all the CPUs have capable of sending SGIs to other CPUs */
> + for_each_online_cpu(i) {
> + if (cpu == i)
> + continue;
> +
> + if (MPIDR_RS(mpidr) && (!per_cpu(has_rss, i))) {
> + pr_crit("CPU%d has no RSS, SGIs aren't reachable to CPU%d",
> + i, cpu);
> + continue;
> + }
> +
> + if (MPIDR_RS(cpu_logical_map(i)) && (!per_cpu(has_rss, cpu))) {
> + pr_crit("CPU%d has no RSS, SGIs aren't reachable to CPU%d",
> + cpu, i);
> + continue;
> + }
> +
> + if (MPIDR_RS(mpidr) || MPIDR_RS(cpu_logical_map(i)))
> + need_rss = true;
> + }

The logic feels a bit clumsy, and fails to warn if the first CPU needs
RSS while the distributor doesn't have it. Yes, that's the ultimate
corner case, but hey, we might as well do the right thing... ;-)

How about something like:

for_each_online_cpu(i) {
bool have_rss = per_cpu(has_rss, i) || per_cpu(has_rss, cpu);
need_rss = MPIDR_RS(mpidr) || MPIDR_RS(cpu_logical_map(i);

if (need_rss != have_rss)
pr_crit("CPU%d (%lx) can't SGI CPU%d (%lx), no RSS\n",
cpu, mpidr, i, cpu_logical_map(i));
}

which is informative enough.

> +
> + /**
> + * GIC spec says, when ICC_CTLR_EL1.RSS==1 and GICD_TYPER.RSS==0,
> + * writing ICC_ASGI1R_EL1 register with RS != 0 is a CONSTRAINED
> + * UNPREDICTABLE choice of :
> + * - The write is ignored.
> + * - The RS field is treated as 0.
> + */
> + if (need_rss && (!gic_data.has_rss))
> + pr_crit("RSS support is required but GICD doesn't support it\n");

This can be turn to a pr_crit_once, as there is no need to scream for
each CPU (the thing is dead anyway).

> }
>
> static int gic_dist_supports_lpis(void)
> @@ -548,6 +589,9 @@ static void gic_cpu_init(void)
>
> #ifdef CONFIG_SMP
>
> +#define MPIDR_TO_SGI_RS(mpidr) (MPIDR_RS(mpidr) << ICC_SGI1R_RS_SHIFT)
> +#define MPIDR_TO_SGI_CLUSTER_ID(mpidr) (mpidr & ~0xFUL)
> +
> static int gic_starting_cpu(unsigned int cpu)
> {
> gic_cpu_init();
> @@ -562,13 +606,6 @@ static u16 gic_compute_target_list(int *base_cpu, const struct cpumask *mask,
> u16 tlist = 0;
>
> while (cpu < nr_cpu_ids) {
> - /*
> - * If we ever get a cluster of more than 16 CPUs, just
> - * scream and skip that CPU.
> - */
> - if (WARN_ON((mpidr & 0xff) >= 16))
> - goto out;
> -
> tlist |= 1 << (mpidr & 0xf);
>
> next_cpu = cpumask_next(cpu, mask);
> @@ -578,7 +615,7 @@ static u16 gic_compute_target_list(int *base_cpu, const struct cpumask *mask,
>
> mpidr = cpu_logical_map(cpu);
>
> - if (cluster_id != (mpidr & ~0xffUL)) {
> + if (cluster_id != MPIDR_TO_SGI_CLUSTER_ID(mpidr)) {
> cpu--;
> goto out;
> }
> @@ -600,6 +637,7 @@ static void gic_send_sgi(u64 cluster_id, u16 tlist, unsigned int irq)
> MPIDR_TO_SGI_AFFINITY(cluster_id, 2) |
> irq << ICC_SGI1R_SGI_ID_SHIFT |
> MPIDR_TO_SGI_AFFINITY(cluster_id, 1) |
> + MPIDR_TO_SGI_RS(cluster_id) |
> tlist << ICC_SGI1R_TARGET_LIST_SHIFT);
>
> pr_debug("CPU%d: ICC_SGI1R_EL1 %llx\n", smp_processor_id(), val);
> @@ -620,7 +658,7 @@ static void gic_raise_softirq(const struct cpumask *mask, unsigned int irq)
> smp_wmb();
>
> for_each_cpu(cpu, mask) {
> - unsigned long cluster_id = cpu_logical_map(cpu) & ~0xffUL;
> + u64 cluster_id = MPIDR_TO_SGI_CLUSTER_ID(cpu_logical_map(cpu));
> u16 tlist;
>
> tlist = gic_compute_target_list(&cpu, mask, cluster_id);
> @@ -959,6 +997,10 @@ static int __init gic_init_bases(void __iomem *dist_base,
> goto out_free;
> }
>
> + gic_data.has_rss = !!(typer & GICD_TYPER_RSS);
> + pr_info("Distributor has %s Range Selector support\n",
> + gic_data.has_rss ? "" : "no");
> +
> set_handle_irq(gic_handle_irq);
>
> if (IS_ENABLED(CONFIG_ARM_GIC_V3_ITS) && gic_dist_supports_lpis())
> diff --git a/include/linux/irqchip/arm-gic-v3.h b/include/linux/irqchip/arm-gic-v3.h
> index 6a1f87f..eb9ff9b 100644
> --- a/include/linux/irqchip/arm-gic-v3.h
> +++ b/include/linux/irqchip/arm-gic-v3.h
> @@ -68,6 +68,7 @@
> #define GICD_CTLR_ENABLE_SS_G1 (1U << 1)
> #define GICD_CTLR_ENABLE_SS_G0 (1U << 0)
>
> +#define GICD_TYPER_RSS (1U << 26)
> #define GICD_TYPER_LPIS (1U << 17)
> #define GICD_TYPER_MBIS (1U << 16)
>
> @@ -377,6 +378,7 @@
> #define ICC_CTLR_EL1_SEIS_MASK (0x1 << ICC_CTLR_EL1_SEIS_SHIFT)
> #define ICC_CTLR_EL1_A3V_SHIFT 15
> #define ICC_CTLR_EL1_A3V_MASK (0x1 << ICC_CTLR_EL1_A3V_SHIFT)
> +#define ICC_CTLR_EL1_RSS (0x1 << 18)
> #define ICC_PMR_EL1_SHIFT 0
> #define ICC_PMR_EL1_MASK (0xff << ICC_PMR_EL1_SHIFT)
> #define ICC_BPR0_EL1_SHIFT 0
> @@ -465,6 +467,8 @@
> #define ICC_SGI1R_AFFINITY_2_SHIFT 32
> #define ICC_SGI1R_AFFINITY_2_MASK (0xffULL << ICC_SGI1R_AFFINITY_2_SHIFT)
> #define ICC_SGI1R_IRQ_ROUTING_MODE_BIT 40
> +#define ICC_SGI1R_RS_SHIFT 44
> +#define ICC_SGI1R_RS_MASK (0xfULL << ICC_SGI1R_RS_SHIFT)
> #define ICC_SGI1R_AFFINITY_3_SHIFT 48
> #define ICC_SGI1R_AFFINITY_3_MASK (0xffULL << ICC_SGI1R_AFFINITY_3_SHIFT)
>
>

Thanks,

M.
--
Jazz is not dead. It just smells funny...

Next message: Roman Gushchin: "Re: [v10 3/6] mm, oom: cgroup-aware OOM killer"
Previous message: Colin King: "[PATCH] platform/x86: mlx-platform: make a couple of structures static"
Next in thread: Shanker Donthineni: "Re: [PATCH v2] irqchip/gicv3: Add support for Range Selector (RS) feature"
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