Re: [PATCH v5 01/23] irqchip/gic-v3: Use SGIs without active state if offered

Auger Eric
2020-03-12T17:17:02Z

Hi Marc,

On 3/4/20 9:33 PM, Marc Zyngier wrote:
> To allow the direct injection of SGIs into a guest, the GICv4.1
> architecture has to sacrifice the Active state so that SGIs look
> a lot like LPIs (they are injected by the same mechanism).
>
> In order not to break existing software, the architecture gives
> offers guests OSs the choice: SGIs with or without an active
nit gives offers
> state. It is the hypervisors duty to honor the guest's choice.
>
> For this, the architecture offers a discovery bit indicating whether
> the GIC supports GICv4.1 SGIs (GICD_TYPER2.nASSGIcap), and another
> bit indicating whether the guest wants Active-less SGIs or not
> (controlled by GICD_CTLR.nASSGIreq).
>
> A hypervisor not supporting GICv4.1 SGIs would leave nASSGIcap
> clear, and a guest not knowing about GICv4.1 SGIs (or definitely
> wanting an Active state) would leave nASSGIreq clear (both being
> thankfully backward compatible with older revisions of the GIC).
>
> Since Linux is perfectly happy without an active state on SGIs,
> inform the hypervisor that we'll use that if offered.
>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> Reviewed-by: Zenghui Yu <yuzenghui@huawei.com>
> ---
> drivers/irqchip/irq-gic-v3.c | 10 ++++++++--
> include/linux/irqchip/arm-gic-v3.h | 2 ++
> 2 files changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
> index cd76435c4a31..73e87e176d76 100644
> --- a/drivers/irqchip/irq-gic-v3.c
> +++ b/drivers/irqchip/irq-gic-v3.c
> @@ -724,6 +724,7 @@ static void __init gic_dist_init(void)
> unsigned int i;
> u64 affinity;
> void __iomem *base = gic_data.dist_base;
> + u32 val;
>
> /* Disable the distributor */
> writel_relaxed(0, base + GICD_CTLR);
> @@ -756,9 +757,14 @@ static void __init gic_dist_init(void)
> /* Now do the common stuff, and wait for the distributor to drain */
> gic_dist_config(base, GIC_LINE_NR, gic_dist_wait_for_rwp);
>
> + val = GICD_CTLR_ARE_NS | GICD_CTLR_ENABLE_G1A | GICD_CTLR_ENABLE_G1;
> + if (gic_data.rdists.gicd_typer2 & GICD_TYPER2_nASSGIcap) {
> + pr_info("Enabling SGIs without active state\n");
> + val |= GICD_CTLR_nASSGIreq;
> + }
> +
> /* Enable distributor with ARE, Group1 */
> - writel_relaxed(GICD_CTLR_ARE_NS | GICD_CTLR_ENABLE_G1A | GICD_CTLR_ENABLE_G1,
> - base + GICD_CTLR);
> + writel_relaxed(val, base + GICD_CTLR);
>
> /*
> * Set all global interrupts to the boot CPU only. ARE must be
> diff --git a/include/linux/irqchip/arm-gic-v3.h b/include/linux/irqchip/arm-gic-v3.h
> index 83439bfb6c5b..c29a02678a6f 100644
> --- a/include/linux/irqchip/arm-gic-v3.h
> +++ b/include/linux/irqchip/arm-gic-v3.h
> @@ -57,6 +57,7 @@
> #define GICD_SPENDSGIR 0x0F20
>
> #define GICD_CTLR_RWP (1U << 31)
> +#define GICD_CTLR_nASSGIreq (1U << 8)
I am not able to find this bit in Arm IHI 0069F (ID022020)
same for the bit in GICD_TYPER. Do we still miss part of the spec?

Thanks

Eric
> #define GICD_CTLR_DS (1U << 6)
> #define GICD_CTLR_ARE_NS (1U << 4)
> #define GICD_CTLR_ENABLE_G1A (1U << 1)
> @@ -90,6 +91,7 @@
> #define GICD_TYPER_ESPIS(typer) \
> (((typer) & GICD_TYPER_ESPI) ? GICD_TYPER_SPIS((typer) >> 27) : 0)
>
> +#define GICD_TYPER2_nASSGIcap (1U << 8)
> #define GICD_TYPER2_VIL (1U << 7)
> #define GICD_TYPER2_VID GENMASK(4, 0)
>
>