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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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