linux-kernel - RE: [PATCH] driver core: platform: expose numa

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Date:   Tue, 2 Jun 2020 05:09:57 +0000
From:   "Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.com>
To:     Greg KH <gregkh@...uxfoundation.org>
CC:     "rafael@...nel.org" <rafael@...nel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linuxarm <linuxarm@...wei.com>,
        "Zengtao (B)" <prime.zeng@...ilicon.com>,
        Robin Murphy <robin.murphy@....com>
Subject: RE: [PATCH] driver core: platform: expose numa_node to users in
 sysfs

> >
> > Platform devices are NUMA?  That's crazy, and feels like a total abuse
> > of platform devices and drivers that really should belong on a "real"
> > bus.
> 
> I am not sure if it is an abuse of platform device. But smmu is a platform
> device,
> drivers/iommu/arm-smmu-v3.c is a platform driver.
> In a typical ARM server, there are maybe multiple SMMU devices which can
> support
> IO virtual address and page tables for other devices on PCI-like busses.
> Each different SMMU device might be close to different NUMA node. There is
> really a hardware topology.
> 
> If you have multiple CPU packages in a NUMA server, some platform devices
> might
> Belong to CPU0, some other might belong to CPU1.

Those devices are populated by acpi_iort for an ARM server:

drivers/acpi/arm64/iort.c:

static const struct iort_dev_config iort_arm_smmu_v3_cfg __initconst = {
        .name = "arm-smmu-v3",
        .dev_dma_configure = arm_smmu_v3_dma_configure,
        .dev_count_resources = arm_smmu_v3_count_resources,
        .dev_init_resources = arm_smmu_v3_init_resources,
        .dev_set_proximity = arm_smmu_v3_set_proximity,
};

void __init acpi_iort_init(void)
{
        acpi_status status;

        status = acpi_get_table(ACPI_SIG_IORT, 0, &iort_table);
        ...
        iort_check_id_count_workaround(iort_table);
        iort_init_platform_devices();
}

static void __init iort_init_platform_devices(void)
{
        ...

        for (i = 0; i < iort->node_count; i++) {
                if (iort_node >= iort_end) {
                        pr_err("iort node pointer overflows, bad table\n");
                        return;
                }

                iort_enable_acs(iort_node);

                ops = iort_get_dev_cfg(iort_node);
                if (ops) {
                        fwnode = acpi_alloc_fwnode_static();
                        if (!fwnode)
                                return;

                        iort_set_fwnode(iort_node, fwnode);

                        ret = iort_add_platform_device(iort_node, ops);
                        if (ret) {
                                iort_delete_fwnode(iort_node);
                                acpi_free_fwnode_static(fwnode);
                                return;
                        }
                }

                ...
        }
...
}

NUMA node is got from ACPI:

static int  __init arm_smmu_v3_set_proximity(struct device *dev,
                                              struct acpi_iort_node *node)
{
        struct acpi_iort_smmu_v3 *smmu;

        smmu = (struct acpi_iort_smmu_v3 *)node->node_data;
        if (smmu->flags & ACPI_IORT_SMMU_V3_PXM_VALID) {
                int dev_node = acpi_map_pxm_to_node(smmu->pxm);

                ...

                set_dev_node(dev, dev_node);
                ...
        }
        return 0;
}

Barry