[PATCH v10 12/14] arm_mpam: detect and enable MPAM-Fb PCC support
Ben Horgan
ben.horgan at arm.com
Tue Sep 15 09:33:36 PDT 2026
Hi Andre,
On 11/09/2026 12:28, Andre Przywara wrote:
> The Arm MPAM-Fb specification [1] describes a protocol to access MSC
> registers through a firmware interface. This requires a shared memory
> region to hold the message, and a mailbox to trigger the access.
> For ACPI this is wrapped as a PCC channel, described using existing
> ACPI abstractions.
>
> Add code to parse those PCC table descriptions associated with an MSC,
> and store the parsed information in the MSC struct.
> There can be multiple PCC channels, and each channel can serve multiple
> MSCs, so we need to keep track of the channel usage, using a list and
> a refcount.
>
> This will be used by the MPAM-Fb access wrapper code.
>
> [1] https://developer.arm.com/documentation/den0144/latest
>
> Signed-off-by: Andre Przywara <andre.przywara at arm.com>
> Tested-by: Ritwick Sharma <ritwick.sharma at arm.com> # on Arm AGI CPU
> Reviewed-by: Jonathan Cameron <jonathan.cameron at oss.qualcomm.com>
> Tested-by: Srivathsa L Rao <srivathsa.rao at oss.qualcomm.com>
> Reviewed-by: Srivathsa L Rao <srivathsa.rao at oss.qualcomm.com>
> Reviewed-by: Gavin Shan <gshan at redhat.com>
> ---
> drivers/resctrl/Kconfig | 1 +
> drivers/resctrl/mpam_devices.c | 119 +++++++++++++++++++++++++++++++-
> drivers/resctrl/mpam_fb.c | 41 +++++++++++
> drivers/resctrl/mpam_internal.h | 2 +
> 4 files changed, 161 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/resctrl/Kconfig b/drivers/resctrl/Kconfig
> index 9591d792736e5..3f81638f57be3 100644
> --- a/drivers/resctrl/Kconfig
> +++ b/drivers/resctrl/Kconfig
> @@ -2,6 +2,7 @@ menuconfig ARM64_MPAM_DRIVER
> bool "MPAM driver"
> depends on ARM64 && ARM64_MPAM
> select ACPI_MPAM if ACPI
> + select PCC if ACPI
> select MAILBOX
> help
> Memory System Resource Partitioning and Monitoring (MPAM) driver for
> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index 14dc8461e4b8f..150a529458388 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c
> @@ -20,14 +20,19 @@
> #include <linux/irqdesc.h>
> #include <linux/list.h>
> #include <linux/lockdep.h>
> +#include <linux/mailbox_client.h>
> #include <linux/mutex.h>
> #include <linux/platform_device.h>
> #include <linux/printk.h>
> +#include <linux/property.h>
> #include <linux/srcu.h>
> #include <linux/spinlock.h>
> #include <linux/types.h>
> #include <linux/workqueue.h>
>
> +#include <acpi/pcc.h>
> +#include <acpi/acpi_io.h>
> +
> #include "mpam_internal.h"
>
> /* Values for the T241 errata workaround */
> @@ -50,6 +55,87 @@ static LIST_HEAD(mpam_all_msc);
>
> struct srcu_struct mpam_srcu;
>
> +/* PCC channels might be serving multiple MSCs, so keep a refcounted list. */
> +static DEFINE_MUTEX(pcc_chan_list_lock);
> +static LIST_HEAD(pcc_chan_list);
> +
> +static void mpam_pcc_chan_release(struct kref *ref)
> +{
> + struct mpam_pcc_chan *cur = container_of(ref, struct mpam_pcc_chan,
> + refcount);
> +
> + pcc_mbox_free_channel(cur->pcc_chan);
> + list_del(&cur->pcc_chans);
> + mutex_destroy(&cur->pcc_chan_lock);
> + kfree(cur);
> +}
> +
> +static struct mpam_pcc_chan *mpam_pcc_chan_get(struct device *dev,
> + int subspace_id)
> +{
> + struct mpam_pcc_chan *cur;
> +
> + guard(mutex)(&pcc_chan_list_lock);
> +
> + list_for_each_entry(cur, &pcc_chan_list, pcc_chans) {
> + if (cur->subspace_id == subspace_id) {
> + kref_get(&cur->refcount);
> +
> + return cur;
> + }
> + }
> +
> + cur = kzalloc_obj(*cur);
> + if (!cur)
> + return ERR_PTR(-ENOMEM);
> +
> + cur->pcc_cl.tx_block = true;
> +
> + cur->pcc_chan = pcc_mbox_request_channel(&cur->pcc_cl, subspace_id);
> + if (IS_ERR(cur->pcc_chan)) {
> + long err = PTR_ERR(cur->pcc_chan);
> +
> + kfree(cur);
> + return ERR_PTR(err);
> + }
> +
> + /*
> + * Timeout based on the "nominal latency" in us, from the
> + * PCC ACPI table. tx_tout is in ms.
> + * Add some margin here to be on the safe side.
> + */
> + cur->pcc_cl.tx_tout = DIV_ROUND_UP(cur->pcc_chan->latency * 5, 1000);
> +
> + mutex_init(&cur->pcc_chan_lock);
> +
> + cur->subspace_id = subspace_id;
> + kref_init(&cur->refcount);
> +
> + list_add_tail(&cur->pcc_chans, &pcc_chan_list);
> +
> + return cur;
> +}
> +
> +static int mpam_pcc_chan_put(struct mpam_pcc_chan *pcc_chan)
> +{
> + struct mpam_pcc_chan *cur, *tmp;
> +
> + if (!pcc_chan)
> + return 0;
> +
> + guard(mutex)(&pcc_chan_list_lock);
> +
> + list_for_each_entry_safe(cur, tmp, &pcc_chan_list, pcc_chans) {
> + if (cur == pcc_chan) {
> + kref_put(&cur->refcount, mpam_pcc_chan_release);
> +
> + return 0;
> + }
> + }
> +
> + return -ENOENT;
> +}
> +
> /*
> * Number of MSCs that have been probed. Once all MSCs have been probed MPAM
> * can be enabled.
> @@ -2285,6 +2371,8 @@ static void mpam_msc_drv_remove(struct platform_device *pdev)
> if (!msc)
> return;
>
> + mpam_pcc_chan_put(msc->pcc_chan);
> +
I think this should be in mpam_msc_destroy() so we don't leak the channel on mpam_disable().
Thanks,
Ben
> mutex_lock(&mpam_list_lock);
> mpam_msc_destroy(msc);
> mutex_unlock(&mpam_list_lock);
> @@ -2295,7 +2383,7 @@ static void mpam_msc_drv_remove(struct platform_device *pdev)
> static struct mpam_msc *do_mpam_msc_drv_probe(struct platform_device *pdev)
> {
> int err;
> - u32 tmp;
> + u32 pcc_subspace_id;
> struct mpam_msc *msc;
> struct resource *msc_res;
> struct device *dev = &pdev->dev;
> @@ -2339,7 +2427,7 @@ static struct mpam_msc *do_mpam_msc_drv_probe(struct platform_device *pdev)
> if (err)
> return ERR_PTR(err);
>
> - if (device_property_read_u32(&pdev->dev, "pcc-channel", &tmp))
> + if (device_property_read_u32(dev, "pcc-channel", &pcc_subspace_id))
> msc->iface = MPAM_IFACE_MMIO;
> else
> msc->iface = MPAM_IFACE_PCC;
> @@ -2360,6 +2448,33 @@ static struct mpam_msc *do_mpam_msc_drv_probe(struct platform_device *pdev)
> }
> msc->mapped_hwpage_sz = msc_res->end - msc_res->start;
> msc->mapped_hwpage = io;
> + } else if (msc->iface == MPAM_IFACE_PCC) {
> + u32 mpam_fb_msc_id;
> +
> + msc->pcc_chan = mpam_pcc_chan_get(dev, pcc_subspace_id);
> + if (IS_ERR(msc->pcc_chan)) {
> + pr_err("Failed to request MSC PCC channel\n");
> + return ERR_CAST(msc->pcc_chan);
> + }
> +
> + err = mpam_fb_check_shared_buffer_size(msc);
> + if (err) {
> + mpam_pcc_chan_put(msc->pcc_chan);
> +
> + return ERR_PTR(err);
> + }
> +
> + err = mpam_fb_check_protocol_version(msc);
> + if (err) {
> + mpam_pcc_chan_put(msc->pcc_chan);
> +
> + return ERR_PTR(err);
> + }
> +
> + if (device_property_read_u32(&pdev->dev, "mpam-fb-msc-id",
> + &mpam_fb_msc_id))
> + mpam_fb_msc_id = msc->id;
> + msc->mpam_fb_msc_id = mpam_fb_msc_id;
> } else {
> return ERR_PTR(-EINVAL);
> }
> diff --git a/drivers/resctrl/mpam_fb.c b/drivers/resctrl/mpam_fb.c
> index 98212f761de38..8fc1d78a7b5ab 100644
> --- a/drivers/resctrl/mpam_fb.c
> +++ b/drivers/resctrl/mpam_fb.c
> @@ -20,10 +20,15 @@
> #define MPAM_FB_PROTOCOL_ID 0x1a
>
> #define MPAM_PROTOCOL_VERSION_CMD 0x0
> +#define MPAM_FB_VERSION_MAJOR_MASK GENMASK_U32(31, 16)
> +#define MPAM_FB_VERSION_MINOR_MASK GENMASK_U32(15, 0)
> +
> #define MPAM_MSC_READ_CMD 0x4
> #define MPAM_MSC_WRITE_CMD 0x5
>
> #define MPAM_FB_PROT_HEADER_LEN sizeof(u32)
> +/* The longest message is MPAM_MSC_WRITE, with 4 parameters. */
> +#define MPAM_FB_MAX_MSG_SIZE (4 * sizeof(u32))
>
> #define MPAM_FB_SUCCESS 0
> #define MPAM_FB_ERR_NOT_SUPPORTED -1
> @@ -209,3 +214,39 @@ int mpam_fb_send_write_request(struct mpam_msc *msc, u16 reg, u32 value)
> return mpam_fb_send_request(msc, msc->mpam_fb_msc_id, reg, &value,
> MPAM_MSC_WRITE_CMD);
> }
> +
> +/* We only support MPAM-Fb protocol version 1.x */
> +int mpam_fb_check_protocol_version(struct mpam_msc *msc)
> +{
> + u32 version;
> + int ret;
> +
> + ret = mpam_fb_send_request(msc, 0, 0, &version,
> + MPAM_PROTOCOL_VERSION_CMD);
> + if (ret)
> + return ret;
> +
> + if (FIELD_GET(MPAM_FB_VERSION_MAJOR_MASK, version) != 1) {
> + pr_err("Incompatible MPAM-Fb protocol version %d.%d\n",
> + FIELD_GET(MPAM_FB_VERSION_MAJOR_MASK, version),
> + FIELD_GET(MPAM_FB_VERSION_MINOR_MASK, version));
> +
> + return -EINVAL;
> + }
> +
> + return 0;
> +}
> +
> +int mpam_fb_check_shared_buffer_size(struct mpam_msc *msc)
> +{
> + int min_buffer_size = MPAM_FB_MAX_MSG_SIZE +
> + sizeof(struct acpi_pcct_ext_pcc_shared_memory);
> +
> + if (msc->pcc_chan->pcc_chan->shmem_size < min_buffer_size) {
> + pr_err("MPAM-Fb PCC channel size too small.\n");
> +
> + return -ENOMEM;
> + }
> +
> + return 0;
> +}
> diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
> index e5a2804facd2d..314d3b48ca9fd 100644
> --- a/drivers/resctrl/mpam_internal.h
> +++ b/drivers/resctrl/mpam_internal.h
> @@ -538,6 +538,8 @@ static inline void mpam_resctrl_teardown_class(struct mpam_class *class) { }
> /* MPAM-Fb Firmware-backed protocol wrappers */
> int mpam_fb_send_read_request(struct mpam_msc *msc, u16 reg, u32 *result);
> int mpam_fb_send_write_request(struct mpam_msc *msc, u16 reg, u32 value);
> +int mpam_fb_check_protocol_version(struct mpam_msc *msc);
> +int mpam_fb_check_shared_buffer_size(struct mpam_msc *msc);
>
> /*
> * MPAM MSCs have the following register layout. See:
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