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Message-ID: <40dd0187-230b-470c-a875-c324df1dedce@arm.com>
Date: Mon, 20 Oct 2025 16:44:53 +0100
From: Ben Horgan <ben.horgan@....com>
To: James Morse <james.morse@....com>, linux-kernel@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, linux-acpi@...r.kernel.org
Cc: D Scott Phillips OS <scott@...amperecomputing.com>,
carl@...amperecomputing.com, lcherian@...vell.com,
bobo.shaobowang@...wei.com, tan.shaopeng@...itsu.com,
baolin.wang@...ux.alibaba.com, Jamie Iles <quic_jiles@...cinc.com>,
Xin Hao <xhao@...ux.alibaba.com>, peternewman@...gle.com,
dfustini@...libre.com, amitsinght@...vell.com,
David Hildenbrand <david@...hat.com>, Dave Martin <dave.martin@....com>,
Koba Ko <kobak@...dia.com>, Shanker Donthineni <sdonthineni@...dia.com>,
fenghuay@...dia.com, baisheng.gao@...soc.com,
Jonathan Cameron <jonathan.cameron@...wei.com>, Rob Herring
<robh@...nel.org>, Rohit Mathew <rohit.mathew@....com>,
Rafael Wysocki <rafael@...nel.org>, Len Brown <lenb@...nel.org>,
Lorenzo Pieralisi <lpieralisi@...nel.org>, Hanjun Guo
<guohanjun@...wei.com>, Sudeep Holla <sudeep.holla@....com>,
Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Danilo Krummrich <dakr@...nel.org>, Jeremy Linton <jeremy.linton@....com>,
Gavin Shan <gshan@...hat.com>
Subject: Re: [PATCH v3 07/29] arm_mpam: Add probe/remove for mpam msc driver
and kbuild boiler plate
Hi James,
On 10/17/25 19:56, James Morse wrote:
> Probing MPAM is convoluted. MSCs that are integrated with a CPU may
> only be accessible from those CPUs, and they may not be online.
> Touching the hardware early is pointless as MPAM can't be used until
> the system-wide common values for num_partid and num_pmg have been
> discovered.
>
> Start with driver probe/remove and mapping the MSC.
>
> CC: Carl Worth <carl@...amperecomputing.com>
> Tested-by: Fenghua Yu <fenghuay@...dia.com>
> Signed-off-by: James Morse <james.morse@....com>
> ---
> Changes since v2:
> * Comment in Kconfig about why EXPERT.
> * Dropped duplicate depends.
> * Fixed duplicate return statement.
> * Restructured driver probe to have a do_ function to allow breaks to be
> return instead...
> * Removed resctrl.h include, added spinlock.h
> * Removed stray DT function prototype
> * Removed stray PCC variables in struct mpam_msc.
> * Used ccflags not cflags for debug define.
> * Moved srcu header include to internal.h
> * Moved mpam_msc_destroy() into this patch.
>
> Changes since v1:
> * Avoid selecting driver on other architectrues.
> * Removed PCC support stub.
> * Use for_each_available_child_of_node_scoped() and of_property_read_reg()
> * Clarified a comment.
> * Stopped using mpam_num_msc as an id,a and made it atomic.
> * Size of -1 returned from cache_of_calculate_id()
> * Renamed some struct members.
> * Made a bunch of pr_err() dev_err_ocne().
> * Used more cleanup magic.
> * Inlined a print message.
> * Fixed error propagation from mpam_dt_parse_resources().
> * Moved cache accessibility checks earlier.
> * Change cleanup macro to use IS_ERR_OR_NULL().
>
> Changes since RFC:
> * Check for status=broken DT devices.
> * Moved all the files around.
> * Made Kconfig symbols depend on EXPERT
> ---
> arch/arm64/Kconfig | 1 +
> drivers/Kconfig | 2 +
> drivers/Makefile | 1 +
> drivers/acpi/arm64/mpam.c | 7 ++
> drivers/resctrl/Kconfig | 13 +++
> drivers/resctrl/Makefile | 4 +
> drivers/resctrl/mpam_devices.c | 190 ++++++++++++++++++++++++++++++++
> drivers/resctrl/mpam_internal.h | 52 +++++++++
> include/linux/acpi.h | 2 +-
> 9 files changed, 271 insertions(+), 1 deletion(-)
> create mode 100644 drivers/resctrl/Kconfig
> create mode 100644 drivers/resctrl/Makefile
> create mode 100644 drivers/resctrl/mpam_devices.c
> create mode 100644 drivers/resctrl/mpam_internal.h
>
[snip]
> +static struct mpam_msc *do_mpam_msc_drv_probe(struct platform_device *pdev)
> +{
> + int err;
> + u32 tmp;
> + struct mpam_msc *msc;
> + struct resource *msc_res;
> + struct device *dev = &pdev->dev;
> +
> + lockdep_assert_held(&mpam_list_lock);
> +
> + msc = devm_kzalloc(&pdev->dev, sizeof(*msc), GFP_KERNEL);
> + if (!msc)
> + return ERR_PTR(-ENOMEM);
> +
> + mutex_init(&msc->probe_lock);
> + mutex_init(&msc->part_sel_lock);
> + msc->id = pdev->id;
> + msc->pdev = pdev;
> + INIT_LIST_HEAD_RCU(&msc->all_msc_list);
> + INIT_LIST_HEAD_RCU(&msc->ris);
> +
> + err = update_msc_accessibility(msc);
> + if (err)
> + return ERR_PTR(err);
> + if (cpumask_empty(&msc->accessibility)) {
> + dev_err_once(dev, "MSC is not accessible from any CPU!");
> + return ERR_PTR(-EINVAL);
> + }
> +
> + if (device_property_read_u32(&pdev->dev, "pcc-channel", &tmp))
> + msc->iface = MPAM_IFACE_MMIO;
> + else
> + msc->iface = MPAM_IFACE_PCC;
As there is no PCC support in this series should this return
ERR_PTR(-ENOTSUPP) when the firmware doesn't advertise a MMIO interface?
> +
> + if (msc->iface == MPAM_IFACE_MMIO) {
> + void __iomem *io;
> +
> + io = devm_platform_get_and_ioremap_resource(pdev, 0,
> + &msc_res);
> + if (IS_ERR(io)) {
> + dev_err_once(dev, "Failed to map MSC base address\n");
> + return (void *)io;
> + }
> + msc->mapped_hwpage_sz = msc_res->end - msc_res->start;
> + msc->mapped_hwpage = io;
> + }
> +
> + list_add_rcu(&msc->all_msc_list, &mpam_all_msc);
> + platform_set_drvdata(pdev, msc);
> +
> + return msc;
> +}
> +
> +static int mpam_msc_drv_probe(struct platform_device *pdev)
> +{
> + int err;
> + struct mpam_msc *msc = NULL;
> + void *plat_data = pdev->dev.platform_data;
> +
> + mutex_lock(&mpam_list_lock);
> + msc = do_mpam_msc_drv_probe(pdev);
> + mutex_unlock(&mpam_list_lock);
> + if (!IS_ERR(msc)) {
> + /* Create RIS entries described by firmware */
> + err = acpi_mpam_parse_resources(msc, plat_data);
> + if (err)
> + mpam_msc_drv_remove(pdev);
> + } else {
> + err = PTR_ERR(msc);
> + }
> +
> + if (!err && atomic_add_return(1, &mpam_num_msc) == fw_num_msc)
> + pr_info("Discovered all MSC\n");
> +
> + return err;
> +}
> +
> +static struct platform_driver mpam_msc_driver = {
> + .driver = {
> + .name = "mpam_msc",
> + },
> + .probe = mpam_msc_drv_probe,
> + .remove = mpam_msc_drv_remove,
> +};
> +
> +static int __init mpam_msc_driver_init(void)
> +{
> + if (!system_supports_mpam())
> + return -EOPNOTSUPP;
> +
> + init_srcu_struct(&mpam_srcu);
> +
> + fw_num_msc = acpi_mpam_count_msc();
> +
> + if (fw_num_msc <= 0) {
> + pr_err("No MSC devices found in firmware\n");
> + return -EINVAL;
> + }
> +
> + return platform_driver_register(&mpam_msc_driver);
> +}
> +subsys_initcall(mpam_msc_driver_init);
--
Thanks,
Ben
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