linux-kernel - Re: [PATCH v3 05/32] irqchip/gic-v4.1: VPE table (aka GICR

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Date:   Mon, 20 Jan 2020 22:03:39 +0800
From:   Zenghui Yu <yuzenghui@...wei.com>
To:     Marc Zyngier <maz@...nel.org>, <kvmarm@...ts.cs.columbia.edu>,
        <linux-kernel@...r.kernel.org>
CC:     Eric Auger <eric.auger@...hat.com>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        "Andrew Murray" <Andrew.Murray@....com>,
        Robert Richter <rrichter@...vell.com>
Subject: Re: [PATCH v3 05/32] irqchip/gic-v4.1: VPE table (aka
 GICR_VPROPBASER) allocation

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@...nel.org>

Reviewed-by: Zenghui Yu <yuzenghui@...wei.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