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SubjectRe: [PATCH 04/35] irqchip/gic-v3: Detect GICv4.1 supporting RVPEID
On Mon, Sep 23, 2019 at 07:25:35PM +0100, Marc Zyngier wrote:
> GICv4.1 supports the RVPEID ("Residency per vPE ID"), which allows for
> a much efficient way of making virtual CPUs resident (to allow direct
> injection of interrupts).
>
> The functionnality needs to be discovered on each and every redistributor
> in the system, and disabled if the settings are inconsistent.
>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
> drivers/irqchip/irq-gic-v3.c | 21 ++++++++++++++++++---
> include/linux/irqchip/arm-gic-v3.h | 2 ++
> 2 files changed, 20 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
> index 422664ac5f53..0b545e2c3498 100644
> --- a/drivers/irqchip/irq-gic-v3.c
> +++ b/drivers/irqchip/irq-gic-v3.c
> @@ -849,8 +849,21 @@ static int __gic_update_rdist_properties(struct redist_region *region,
> void __iomem *ptr)
> {
> u64 typer = gic_read_typer(ptr + GICR_TYPER);
> +
> gic_data.rdists.has_vlpis &= !!(typer & GICR_TYPER_VLPIS);
> - gic_data.rdists.has_direct_lpi &= !!(typer & GICR_TYPER_DirectLPIS);
> +
> + /* RVPEID implies some form of DirectLPI, no matter what the doc says... :-/ */

I think the doc says, RVPEID is *always* 1 for GICv4.1 (and presumably beyond)
and when RVPEID==1 then DirectLPI is *always* 0 - but that's OK because for
GICv4.1 support for direct LPIs is mandatory.

> + gic_data.rdists.has_rvpeid &= !!(typer & GICR_TYPER_RVPEID);
> + gic_data.rdists.has_direct_lpi &= (!!(typer & GICR_TYPER_DirectLPIS) |
> + gic_data.rdists.has_rvpeid);
> +
> + /* Detect non-sensical configurations */
> + if (WARN_ON_ONCE(gic_data.rdists.has_rvpeid && !gic_data.rdists.has_vlpis)) {

How feasible is the following suitation? All the redistributors in the system has
vlpis=0, and only the first redistributor has rvpeid=1 (with the remaining ones
rvpeid=0). If we evaluate this WARN_ON_ONCE on each call to
__gic_update_rdist_properties we end up without direct LPI support, however if we
evaluated this after iterating through all the redistributors then we'd end up
with direct LPI support and a non-essential WARN.

Should we do the WARN after iterating through all the redistributors once we
know what the final values of these flags will be, perhaps in
gic_update_rdist_properties?

> + gic_data.rdists.has_direct_lpi = false;
> + gic_data.rdists.has_vlpis = false;
> + gic_data.rdists.has_rvpeid = false;
> + }
> +
> gic_data.ppi_nr = min(GICR_TYPER_NR_PPIS(typer), gic_data.ppi_nr);
>
> return 1;
> @@ -863,9 +876,10 @@ static void gic_update_rdist_properties(void)
> if (WARN_ON(gic_data.ppi_nr == UINT_MAX))
> gic_data.ppi_nr = 0;
> pr_info("%d PPIs implemented\n", gic_data.ppi_nr);
> - pr_info("%sVLPI support, %sdirect LPI support\n",
> + pr_info("%sVLPI support, %sdirect LPI support, %sRVPEID support\n",
> !gic_data.rdists.has_vlpis ? "no " : "",
> - !gic_data.rdists.has_direct_lpi ? "no " : "");
> + !gic_data.rdists.has_direct_lpi ? "no " : "",
> + !gic_data.rdists.has_rvpeid ? "no " : "");
> }
>
> /* Check whether it's single security state view */
> @@ -1546,6 +1560,7 @@ static int __init gic_init_bases(void __iomem *dist_base,
> &gic_data);
> irq_domain_update_bus_token(gic_data.domain, DOMAIN_BUS_WIRED);
> gic_data.rdists.rdist = alloc_percpu(typeof(*gic_data.rdists.rdist));
> + gic_data.rdists.has_rvpeid = true;
> gic_data.rdists.has_vlpis = true;
> gic_data.rdists.has_direct_lpi = true;
>
> diff --git a/include/linux/irqchip/arm-gic-v3.h b/include/linux/irqchip/arm-gic-v3.h
> index 5cc10cf7cb3e..b34e0c113697 100644
> --- a/include/linux/irqchip/arm-gic-v3.h
> +++ b/include/linux/irqchip/arm-gic-v3.h
> @@ -234,6 +234,7 @@
> #define GICR_TYPER_VLPIS (1U << 1)
> #define GICR_TYPER_DirectLPIS (1U << 3)
> #define GICR_TYPER_LAST (1U << 4)
> +#define GICR_TYPER_RVPEID (1U << 7)
>
> #define GIC_V3_REDIST_SIZE 0x20000
>
> @@ -613,6 +614,7 @@ struct rdists {
> u64 flags;
> u32 gicd_typer;
> bool has_vlpis;
> + bool has_rvpeid;
> bool has_direct_lpi;
> };
>
> --
> 2.20.1
>

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