Re: [PATCH v3 07/29] arm_mpam: Add probe/remove for mpam msc driver and kbuild boiler plate

[Jonathan Cameron <jonathan.cameron@huawei.com>]

On Fri, 17 Oct 2025 18:56:23 +0000
James Morse <james.morse@arm.com> 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@os.amperecomputing.com>
> Tested-by: Fenghua Yu <fenghuay@nvidia.com>
> Signed-off-by: James Morse <james.morse@arm.com>

Trying not to replicate comments too much...

A few things inline but others found bigger stuff to fix.
> diff --git a/drivers/resctrl/Kconfig b/drivers/resctrl/Kconfig
> new file mode 100644
> index 000000000000..58c83b5c8bfd
> --- /dev/null
> +++ b/drivers/resctrl/Kconfig
> @@ -0,0 +1,13 @@
> +menuconfig ARM64_MPAM_DRIVER
> +	bool "MPAM driver"
> +	depends on ARM64 && ARM64_MPAM && EXPERT
> +	help
> +	  MPAM driver for System IP, e,g. caches and memory controllers.

Bit minimal for help text :)

> +
> +if ARM64_MPAM_DRIVER

I'd add a blank line here.

> +config ARM64_MPAM_DRIVER_DEBUG
> +	bool "Enable debug messages from the MPAM driver"
> +	help
> +	  Say yes here to enable debug messages from the MPAM driver.
> +
> +endif

> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> new file mode 100644
> index 000000000000..d18eeec95f79
> --- /dev/null
> +++ b/drivers/resctrl/mpam_devices.c

> +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);
Maybe worth
	err = devm_mutex_init(&msc->probe_lock);
	if (err)
		return err;
to enable the mutex debugging if anyone wants it.  I've stopped trying
to analyze whether that is useful or not, now it is easy to add to drivers
already doing devm.

> +	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;
> +
> +	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;

ERR_CAST() is there to make this stuff more obvious

> +		}
> +		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;
> +}

> diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
> new file mode 100644
> index 000000000000..6ac75f3613c3
> --- /dev/null
> +++ b/drivers/resctrl/mpam_internal.h
> @@ -0,0 +1,52 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +// Copyright (C) 2025 Arm Ltd.
> +
> +#ifndef MPAM_INTERNAL_H
> +#define MPAM_INTERNAL_H
> +
> +#include <linux/arm_mpam.h>
> +#include <linux/cpumask.h>
> +#include <linux/io.h>
> +#include <linux/mailbox_client.h>
> +#include <linux/mutex.h>
> +#include <linux/sizes.h>
> +#include <linux/spinlock.h>
> +#include <linux/srcu.h>

Includes need another look.

Should be seeing the list header for starters and
mailbox_client.h doesn't make sense yet.  Some of the
others may need pushing to the patches where they are
first used or pushing down into the c files that need them.

> +
> +struct platform_device;
> +
> +struct mpam_msc {
> +	/* member of mpam_all_msc */
> +	struct list_head        all_msc_list;
> +
> +	int			id;
> +	struct platform_device *pdev;
> +
> +	/* Not modified after mpam_is_enabled() becomes true */
> +	enum mpam_msc_iface	iface;
> +	u32			nrdy_usec;
> +	cpumask_t		accessibility;
> +
> +	/*
> +	 * probe_lock is only taken during discovery. After discovery these
> +	 * properties become read-only and the lists are protected by SRCU.
> +	 */
> +	struct mutex		probe_lock;
> +	unsigned long		ris_idxs;
> +	u32			ris_max;
> +
> +	/* mpam_msc_ris of this component */
> +	struct list_head	ris;
> +
> +	/*
> +	 * part_sel_lock protects access to the MSC hardware registers that are
> +	 * affected by MPAMCFG_PART_SEL. (including the ID registers that vary
> +	 * by RIS).
> +	 * If needed, take msc->probe_lock first.
> +	 */
> +	struct mutex		part_sel_lock;
> +
> +	void __iomem		*mapped_hwpage;
> +	size_t			mapped_hwpage_sz;
> +};
> +#endif /* MPAM_INTERNAL_H */