Subject: [PATCH 2/6] irqchip: GIC: Convert to EOImode == 1

From: [email-masked] (Eric Auger)
Date: Tue, 11 Aug 2015 11:15:16 +0200

Hi Marc,
On 07/09/2015 03:19 PM, Marc Zyngier wrote:
> So far, GICv2 has been used in with EOImode == 0. The effect of this
> mode is to perform the priority drop and the deactivation of the
> interrupt at the same time.
> 
> While this works perfectly for Linux (we only have a single priority),
> it causes issues when an interrupt is forwarded to a guest, and when
> we want the guest to perform the EOI itself.
> 
> For this case, the GIC architecture provides EOImode == 1, where:
> - A write to the EOI register drops the priority of the interrupt and leaves
> it active. Other interrupts at the same priority level can now be taken,
> but the active interrupt cannot be taken again
> - A write to the DIR marks the interrupt as inactive, meaning it can
> now be taken again.
> 
> We only enable this feature when booted in HYP mode and that
> the device-tree reporte
reported
 a suitable CPU interface. Observable behaviour
> should remain unchanged.
> 
> Signed-off-by: Marc Zyngier <[email-masked]>
> ---
>  drivers/irqchip/irq-gic.c       | 32 +++++++++++++++++++++++++++++---
>  include/linux/irqchip/arm-gic.h |  4 ++++
>  2 files changed, 33 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c
> index 8d7e1c8..e264675 100644
> --- a/drivers/irqchip/irq-gic.c
> +++ b/drivers/irqchip/irq-gic.c
> @@ -46,6 +46,7 @@
>  #include <asm/irq.h>
>  #include <asm/exception.h>
>  #include <asm/smp_plat.h>
> +#include <asm/virt.h>
>  
>  #include "irq-gic-common.h"
>  #include "irqchip.h"
> @@ -82,6 +83,8 @@ static DEFINE_RAW_SPINLOCK(irq_controller_lock);
>  #define NR_GIC_CPU_IF 8
>  static u8 gic_cpu_map[NR_GIC_CPU_IF] __read_mostly;
>  
> +static struct static_key supports_deactivate = STATIC_KEY_INIT_TRUE;
> +
>  #ifndef MAX_GIC_NR
>  #define MAX_GIC_NR	1
>  #endif
> @@ -164,7 +167,10 @@ static void gic_unmask_irq(struct irq_data *d)
>  
>  static void gic_eoi_irq(struct irq_data *d)
>  {
> -	writel_relaxed(gic_irq(d), gic_cpu_base(d) + GIC_CPU_EOI);
> +	if (static_key_true(&supports_deactivate))
> +		writel_relaxed(gic_irq(d), gic_cpu_base(d) + GIC_CPU_DEACTIVATE);
> +	else
> +		writel_relaxed(gic_irq(d), gic_cpu_base(d) + GIC_CPU_EOI);
>  }
>  
>  static int gic_irq_set_irqchip_state(struct irq_data *d,
> @@ -272,11 +278,15 @@ static void __exception_irq_entry gic_handle_irq(struct pt_regs *regs)
>  		irqnr = irqstat & GICC_IAR_INT_ID_MASK;
>  
>  		if (likely(irqnr > 15 && irqnr < 1021)) {
shouldn't we have < 1020?
> +			if (static_key_true(&supports_deactivate))
> +				writel_relaxed(irqstat, cpu_base + GIC_CPU_EOI);
>  			handle_domain_irq(gic->domain, irqnr, regs);
why don't we handle the returned value of handle_domain_irq as we do in
GICv3?
>  			continue;
>  		}
>  		if (irqnr < 16) {
>  			writel_relaxed(irqstat, cpu_base + GIC_CPU_EOI);
> +			if (static_key_true(&supports_deactivate))
> +				writel_relaxed(irqstat, cpu_base + GIC_CPU_DEACTIVATE);
>  #ifdef CONFIG_SMP
>  			handle_IPI(irqnr, regs);
>  #endif
> @@ -358,7 +368,11 @@ static u8 gic_get_cpumask(struct gic_chip_data *gic)
>  static void gic_cpu_if_up(void)
>  {
>  	void __iomem *cpu_base = gic_data_cpu_base(&gic_data[0]);
> -	u32 bypass = 0;
> +	u32 bypass;
> +	u32 mode = 0;
> +
> +	if (static_key_true(&supports_deactivate))
> +		mode = GIC_CPU_CTRL_EOImodeNS;
>  
>  	/*
>  	* Preserve bypass disable bits to be written back later
> @@ -366,7 +380,7 @@ static void gic_cpu_if_up(void)
>  	bypass = readl(cpu_base + GIC_CPU_CTRL);
>  	bypass &= GICC_DIS_BYPASS_MASK;
>  
> -	writel_relaxed(bypass | GICC_ENABLE, cpu_base + GIC_CPU_CTRL);
> +	writel_relaxed(bypass | mode | GICC_ENABLE, cpu_base + GIC_CPU_CTRL);
>  }
>  
>  
> @@ -986,6 +1000,9 @@ void __init gic_init_bases(unsigned int gic_nr, int irq_start,
>  		register_cpu_notifier(&gic_cpu_notifier);
>  #endif
>  		set_handle_irq(gic_handle_irq);
> +		pr_info ("GIC: Using EOImode == %d\n",
> +			 static_key_true(&supports_deactivate));
> +
>  	}
>  
>  	gic_dist_init(gic);
> @@ -1001,6 +1018,7 @@ gic_of_init(struct device_node *node, struct device_node *parent)
>  {
>  	void __iomem *cpu_base;
>  	void __iomem *dist_base;
> +	struct resource cpu_res;
>  	u32 percpu_offset;
>  	int irq;
>  
> @@ -1013,6 +1031,11 @@ gic_of_init(struct device_node *node, struct device_node *parent)
>  	cpu_base = of_iomap(node, 1);
>  	WARN(!cpu_base, "unable to map gic cpu registers\n");
>  
> +	of_address_to_resource(node, 1, &cpu_res);
> +	if (!gic_cnt &&
> +	    (!is_hyp_mode_available() || resource_size(&cpu_res) < SZ_8K))
I don't understand why we check this size?
in GICv1 EOIMode necessarily is 0, right? is it related?

Best Regards

Eric
> +		static_key_slow_dec(&supports_deactivate);
> +
>  	if (of_property_read_u32(node, "cpu-offset", &percpu_offset))
>  		percpu_offset = 0;
>  
> @@ -1131,6 +1154,9 @@ gic_v2_acpi_init(struct acpi_table_header *table)
>  		return -ENOMEM;
>  	}
>  
> +	if (!is_hyp_mode_available())
> +		static_key_slow_dec(&supports_deactivate);
> +
>  	/*
>  	 * Initialize zero GIC instance (no multi-GIC support). Also, set GIC
>  	 * as default IRQ domain to allow for GSI registration and GSI to IRQ
> diff --git a/include/linux/irqchip/arm-gic.h b/include/linux/irqchip/arm-gic.h
> index 9de976b..b1533c0 100644
> --- a/include/linux/irqchip/arm-gic.h
> +++ b/include/linux/irqchip/arm-gic.h
> @@ -20,9 +20,13 @@
>  #define GIC_CPU_ALIAS_BINPOINT		0x1c
>  #define GIC_CPU_ACTIVEPRIO		0xd0
>  #define GIC_CPU_IDENT			0xfc
> +#define GIC_CPU_DEACTIVATE		0x1000
>  
>  #define GICC_ENABLE			0x1
>  #define GICC_INT_PRI_THRESHOLD		0xf0
> +
> +#define GIC_CPU_CTRL_EOImodeNS		(1 << 9)
> +
>  #define GICC_IAR_INT_ID_MASK		0x3ff
>  #define GICC_INT_SPURIOUS		1023
>  #define GICC_DIS_BYPASS_MASK		0x1e0
>