Re: [PATCH v3 05/32] irqchip/gic-v4.1: VPE table (aka GICR_VPROPBASER) allocation

Zenghui Yu
2020-01-20T14:03:53Z

Hi Marc,

On 2019/12/24 19:10, Marc Zyngier wrote:
> GICv4.1 defines a new VPE table that is potentially shared between
> both the ITSs and the redistributors, following complicated affinity
> rules.
>
> To make things more confusing, the programming of this table at
> the redistributor level is reusing the GICv4.0 GICR_VPROPBASER register
> for something completely different.
>
> The code flow is somewhat complexified by the need to respect the
> affinities required by the HW, meaning that tables can either be
> inherited from a previously discovered ITS or redistributor.
>
> Signed-off-by: Marc Zyngier <maz@kernel.org>

Reviewed-by: Zenghui Yu <yuzenghui@huawei.com>

With two very minor concerns below.

[...]

> +static int allocate_vpe_l1_table(void)
> +{
> + void __iomem *vlpi_base = gic_data_rdist_vlpi_base();
> + u64 val, gpsz, npg, pa;
> + unsigned int psz = SZ_64K;
> + unsigned int np, epp, esz;
> + struct page *page;
> +
> + if (!gic_rdists->has_rvpeid)
> + return 0;
> +
> + /*
> + * if VPENDBASER.Valid is set, disable any previously programmed
> + * VPE by setting PendingLast while clearing Valid. This has the
> + * effect of making sure no doorbell will be generated and we can
> + * then safely clear VPROPBASER.Valid.
> + */
> + if (gits_read_vpendbaser(vlpi_base + GICR_VPENDBASER) & GICR_VPENDBASER_Valid)
> + gits_write_vpendbaser(GICR_VPENDBASER_PendingLast,
> + vlpi_base + GICR_VPENDBASER);

I'm confused here. The Valid field resets to 0. Under which scenario
will the Valid==1 while we're doing initialization for this RD?

> +
> + /*
> + * If we can inherit the configuration from another RD, let's do
> + * so. Otherwise, we have to go through the allocation process. We
> + * assume that all RDs have the exact same requirements, as
> + * nothing will work otherwise.
> + */
> + val = inherit_vpe_l1_table_from_rd(&gic_data_rdist()->vpe_table_mask);
> + if (val & GICR_VPROPBASER_4_1_VALID)
> + goto out;
> +
> + gic_data_rdist()->vpe_table_mask = kzalloc(sizeof(cpumask_t), GFP_KERNEL);
> + if (!gic_data_rdist()->vpe_table_mask)
> + return -ENOMEM;
> +
> + val = inherit_vpe_l1_table_from_its();
> + if (val & GICR_VPROPBASER_4_1_VALID)
> + goto out;
> +
> + /* First probe the page size */
> + val = FIELD_PREP(GICR_VPROPBASER_4_1_PAGE_SIZE, GIC_PAGE_SIZE_64K);
> + gits_write_vpropbaser(val, vlpi_base + GICR_VPROPBASER);
> + val = gits_read_vpropbaser(vlpi_base + GICR_VPROPBASER);
> + gpsz = FIELD_GET(GICR_VPROPBASER_4_1_PAGE_SIZE, val);
> + esz = FIELD_GET(GICR_VPROPBASER_4_1_ENTRY_SIZE, val);
> +
> + switch (gpsz) {
> + default:
> + gpsz = GIC_PAGE_SIZE_4K;
> + /* fall through */
> + case GIC_PAGE_SIZE_4K:
> + psz = SZ_4K;
> + break;
> + case GIC_PAGE_SIZE_16K:
> + psz = SZ_16K;
> + break;
> + case GIC_PAGE_SIZE_64K:
> + psz = SZ_64K;
> + break;
> + }
> +
> + /*
> + * Start populating the register from scratch, including RO fields
> + * (which we want to print in debug cases...)
> + */
> + val = 0;
> + val |= FIELD_PREP(GICR_VPROPBASER_4_1_PAGE_SIZE, gpsz);
> + val |= FIELD_PREP(GICR_VPROPBASER_4_1_ENTRY_SIZE, esz);
> +
> + /* How many entries per GIC page? */
> + esz++;
> + epp = psz / (esz * SZ_8);
> +
> + /*
> + * If we need more than just a single L1 page, flag the table
> + * as indirect and compute the number of required L1 pages.
> + */
> + if (epp < ITS_MAX_VPEID) {
> + int nl2;
> +
> + gic_rdists->flags |= RDIST_FLAGS_VPE_INDIRECT;

This flag is set but not used, can we just drop it?

Thanks,
Zenghui