From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 3C0BD421227; Thu, 23 Jul 2026 14:22:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784816540; cv=none; b=EEWRECifWpP2ZD4gcU5d9kXfXV58kq+8PJjPKmPF0Dd1UYrvqbaCbGR8lb0n8slqzxWaAZCfBMO8itjoz6DjuKA8nX4ZN4d4jf6fj/CnQduskrEzp2x3lWbKaaa9nqJ2biiLUMI5m7OD5Fmn+w7fVrOeiPGmBodAZLZeTvSGGY0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784816540; c=relaxed/simple; bh=ZCqx8MSVps/+951UNVfzTb9X0CZwGFa9c4Y6yMpxaow=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=QeUbRGqtLf2mVAXVDBd618TZknEVanls7J4diHUs59DKFSZejOfe/8IZlfpQLOiRlllIXSMq/nGt/IRrTy5jANc7BLnk3/5o3G+M4cECHGxZHoMF5LtLwCpvbdqU7UDcdZfBxMm/Nb/V5TTOFcVfRxYVtpwor1RCutGFZO4HQ1Q= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=VobslA3x; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="VobslA3x" Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 95F77176B; Thu, 23 Jul 2026 07:22:09 -0700 (PDT) Received: from [10.2.212.8] (e134344.arm.com [10.2.212.8]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 01E603F59E; Thu, 23 Jul 2026 07:22:10 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1784816533; bh=ZCqx8MSVps/+951UNVfzTb9X0CZwGFa9c4Y6yMpxaow=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=VobslA3xYWPE8RNDGVTKkwJF9nD4FHjRBnu96bGk/7iBTyJwRkUlTa8fddVfU9Orz R2m4cWgNOUWksD+4R2k2hDZtWPkTmxdQWVFWY36Qa/yElYZzqvbMNPg2uhxywDrmZF 3dZWi3xYOHQgkiqwKwkzu51K8PEr5+IAObY52rE4= Message-ID: <37469c95-cb8b-41e9-9667-e59a324d483d@arm.com> Date: Thu, 23 Jul 2026 15:22:09 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Thunderbird Daily Subject: Re: [PATCH v3 14/16] arm_mpam: add MPAM-Fb MSC firmware access support To: Andre Przywara , Lorenzo Pieralisi , Hanjun Guo , Sudeep Holla , Catalin Marinas , Will Deacon , "Rafael J . Wysocki" , Len Brown , James Morse , Reinette Chatre , Fenghua Yu Cc: Jonathan Cameron , Srivathsa L Rao , Ganapatrao Kulkarni , Trilok Soni , Srinivas Ramana , Niyas Sait , linux-acpi@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <20260710144520.917375-1-andre.przywara@arm.com> <20260710144520.917375-15-andre.przywara@arm.com> Content-Language: en-US From: Ben Horgan In-Reply-To: <20260710144520.917375-15-andre.przywara@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Hi Andre, On 7/10/26 15:45, Andre Przywara wrote: > The Arm MPAM Firmware-backed (Fb) Profile document[1] describes an > alternative way of accessing the "Memory System Components" (MSC) in an > MPAM enabled system. > Normally the MSCs are MMIO mapped, but in some implementations this > might not be possible (MSC located outside of the local socket, MSC > mapped secure-only) or desirable (direct MMIO access too slow or needs > to be mediated through a control processor). MPAM-fb standardises a > protocol to abstract MSC accesses, building on the SCMI protocol. > > Add functions that do an MSC read or write access by redirecting the > request through a firmware interface. For now this done via an ACPI > PCC shared memory and mailbox combination. > > Since the protocol used is only a small subset of the full SCMI spec, > and the SCMI protocol has no full ACPI support anyway, open-code the > SCMI message generation and handshake, for just the fields we need. > > [1] https://developer.arm.com/documentation/den0144/latest > > Signed-off-by: Andre Przywara > --- > drivers/resctrl/Makefile | 2 +- > drivers/resctrl/mpam_devices.c | 26 +++- > drivers/resctrl/mpam_fb.c | 208 ++++++++++++++++++++++++++++++++ > drivers/resctrl/mpam_internal.h | 20 +++ > include/linux/arm_mpam.h | 2 +- > 5 files changed, 251 insertions(+), 7 deletions(-) > create mode 100644 drivers/resctrl/mpam_fb.c > > diff --git a/drivers/resctrl/Makefile b/drivers/resctrl/Makefile > index 4f6d0e81f9b8..097c036724e9 100644 > --- a/drivers/resctrl/Makefile > +++ b/drivers/resctrl/Makefile > @@ -1,5 +1,5 @@ > obj-$(CONFIG_ARM64_MPAM_DRIVER) += mpam.o > -mpam-y += mpam_devices.o > +mpam-y += mpam_devices.o mpam_fb.o > mpam-$(CONFIG_ARM64_MPAM_RESCTRL_FS) += mpam_resctrl.o > > ccflags-$(CONFIG_ARM64_MPAM_DRIVER_DEBUG) += -DDEBUG > diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c > index ca73029654b6..4d3e642486d4 100644 > --- a/drivers/resctrl/mpam_devices.c > +++ b/drivers/resctrl/mpam_devices.c > @@ -181,6 +181,9 @@ static int __mpam_read_reg(struct mpam_msc *msc, u16 reg, u32 *res) > { > WARN_ON_ONCE(!cpumask_test_cpu(smp_processor_id(), &msc->accessibility)); > > + if (msc->iface == MPAM_IFACE_PCC) > + return mpam_fb_send_read_request(msc, reg, res); > + > *res = readl_relaxed(msc->mapped_hwpage + reg); > > return 0; > @@ -197,9 +200,12 @@ static inline int _mpam_read_partsel_reg(struct mpam_msc *msc, u16 reg, > > static int __mpam_write_reg(struct mpam_msc *msc, u16 reg, u32 val) > { > - WARN_ON_ONCE(reg + sizeof(u32) > msc->mapped_hwpage_sz); > WARN_ON_ONCE(!cpumask_test_cpu(smp_processor_id(), &msc->accessibility)); > > + if (msc->iface == MPAM_IFACE_PCC) > + return mpam_fb_send_write_request(msc, reg, val); > + > + WARN_ON_ONCE(reg + sizeof(u32) > msc->mapped_hwpage_sz); > writel_relaxed(val, msc->mapped_hwpage + reg); > > return 0; > @@ -1133,7 +1139,8 @@ static int mpam_msc_read_mbwu_l(struct mpam_msc *msc, u64 *res) > > mpam_mon_sel_lock_held(msc); > > - WARN_ON_ONCE((MSMON_MBWU_L + sizeof(u64)) > msc->mapped_hwpage_sz); > + if (msc->iface == MPAM_IFACE_MMIO) > + WARN_ON_ONCE((MSMON_MBWU_L + sizeof(u64)) > msc->mapped_hwpage_sz); > WARN_ON_ONCE(!cpumask_test_cpu(smp_processor_id(), &msc->accessibility)); > > ret = __mpam_read_reg(msc, MSMON_MBWU_L + 4, &mbwu_l_high2); > @@ -1481,9 +1488,15 @@ static int _msmon_read(struct mpam_component *comp, struct mon_read *arg) > srcu_read_lock_held(&mpam_srcu)) { > arg->ris = ris; > > - err = smp_call_function_any(&msc->accessibility, > - __ris_msmon_read, arg, > - true); > + if (msc->iface == MPAM_IFACE_MMIO) { > + err = smp_call_function_any(&msc->accessibility, > + __ris_msmon_read, > + arg, true); > + } else { > + __ris_msmon_read(arg); > + err = 0; > + } > + > if (!err && arg->err) > err = arg->err; > > @@ -1922,6 +1935,9 @@ static int mpam_get_msc_preferred_cpu(struct mpam_msc *msc) > > static int mpam_touch_msc(struct mpam_msc *msc, int (*fn)(void *a), void *arg) > { > + if (msc->iface != MPAM_IFACE_MMIO) > + return fn(arg); > + > lockdep_assert_irqs_enabled(); > lockdep_assert_cpus_held(); > WARN_ON_ONCE(!srcu_read_lock_held((&mpam_srcu))); > diff --git a/drivers/resctrl/mpam_fb.c b/drivers/resctrl/mpam_fb.c > new file mode 100644 > index 000000000000..7d7409910f28 > --- /dev/null > +++ b/drivers/resctrl/mpam_fb.c > @@ -0,0 +1,208 @@ > +// SPDX-License-Identifier: GPL-2.0 > +// Copyright (C) 2024 Arm Ltd. > + > +#include > +#include > +#include > +#include > +#include > +#include > +#include > +#include > +#include > +#include > +#include > +#include > +#include > +#include > +#include > +#include > + > +#include > + > +#include > + > +#include "mpam_internal.h" > + > +#define MPAM_FB_PROTOCOL_ID 0x1a > +#define MPAM_PROTOCOL_VERSION 0x0 > +#define MPAM_MSC_ATTRIBUTES_CMD 0x3 > +#define MPAM_MSC_READ_CMD 0x4 > +#define MPAM_MSC_WRITE_CMD 0x5 > + > +#define MPAM_FB_ERR_SUCCESS 0 > +#define MPAM_FB_ERR_NOT_SUPPORTED -1 > +#define MPAM_FB_ERR_INVALID_PARAMETERS -2 > +#define MPAM_FB_ERR_DENIED -3 > +#define MPAM_FB_ERR_NOT_FOUND -4 > +#define MPAM_FB_ERR_OUT_OF_RANGE -5 > +#define MPAM_FB_ERR_BUSY -6 > +#define MPAM_FB_ERR_COMMS_ERROR -7 > +#define MPAM_FB_ERR_GENERIC_ERROR -8 > +#define MPAM_FB_ERR_HW_ERROR -9 > +#define MPAM_FB_ERR_PROTOCOL_ERROR -10 > +#define MPAM_FB_ERR_IN_USE -11 > + > +#define MPAM_MSC_PROT_ID_MASK GENMASK(17, 10) > +#define MPAM_MSC_TOKEN_MASK GENMASK(27, 18) > + > +struct mpam_fb_access_payload { > + u32 msc_id; > + u32 flags; > + u32 reg_offset; > + u32 value; > +} __packed; > + > +#define PCC_CHAN_FLAGS_IRQ BIT(0) > +#define MPAM_VERSION_MSG_SIZE (PCC_TYPE3_MSG_PAYLOAD_OFS) > +#define MPAM_READ_MSG_SIZE (PCC_TYPE3_MSG_PAYLOAD_OFS + 3 * sizeof(u32)) > +#define MPAM_WRITE_MSG_SIZE (PCC_TYPE3_MSG_PAYLOAD_OFS + 4 * sizeof(u32)) > + > +static atomic_t mpam_fb_token = ATOMIC_INIT(0); > + > +static int mpam_fb_build_version_message(unsigned int token, > + void __iomem *msg_buf) > +{ > + struct acpi_pcct_ext_pcc_shared_memory *pcc_shmem = msg_buf; I should have occurred to me earlier but I've just put this series through sparse and there are quite a few "incorrect type" warnings generated in mpam_fb.c. For example: ../drivers/resctrl/mpam_fb.c:66:61: warning: incorrect type in initializer (different address spaces) ../drivers/resctrl/mpam_fb.c:66:61: expected struct acpi_pcct_ext_pcc_shared_memory *pcc_shmem ../drivers/resctrl/mpam_fb.c:66:61: got void [noderef] __iomem *msg_buf Thanks, Ben > + > + writel_relaxed(0, &pcc_shmem->flags); > + writel_relaxed(MPAM_VERSION_MSG_SIZE, &pcc_shmem->length); > + writel_relaxed(MPAM_PROTOCOL_VERSION | > + FIELD_PREP(MPAM_MSC_TOKEN_MASK, token) | > + FIELD_PREP(MPAM_MSC_PROT_ID_MASK, MPAM_FB_PROTOCOL_ID), > + &pcc_shmem->command); > + > + return MPAM_VERSION_MSG_SIZE; > +} > + > +static int mpam_fb_build_read_message(int msc_id, int reg, unsigned int token, > + void __iomem *msg_buf) > +{ > + struct acpi_pcct_ext_pcc_shared_memory *pcc_shmem = msg_buf; > + struct mpam_fb_access_payload *payload = msg_buf + sizeof(*pcc_shmem); > + > + writel_relaxed(0, &pcc_shmem->flags); > + writel_relaxed(MPAM_READ_MSG_SIZE, &pcc_shmem->length); > + writel_relaxed(MPAM_MSC_READ_CMD | > + FIELD_PREP(MPAM_MSC_TOKEN_MASK, token) | > + FIELD_PREP(MPAM_MSC_PROT_ID_MASK, MPAM_FB_PROTOCOL_ID), > + &pcc_shmem->command); > + > + writel_relaxed(msc_id, &payload->msc_id); > + writel_relaxed(0, &payload->flags); > + writel_relaxed(reg, &payload->reg_offset); > + > + return MPAM_READ_MSG_SIZE; > +} > + > +static int mpam_fb_build_write_message(int msc_id, int reg, u32 val, > + unsigned int token, > + void __iomem *msg_buf) > +{ > + struct acpi_pcct_ext_pcc_shared_memory *pcc_shmem = msg_buf; > + struct mpam_fb_access_payload *payload = msg_buf + sizeof(*pcc_shmem); > + > + writel_relaxed(0, &pcc_shmem->flags); > + writel_relaxed(MPAM_WRITE_MSG_SIZE, &pcc_shmem->length); > + writel_relaxed(MPAM_MSC_WRITE_CMD | > + FIELD_PREP(MPAM_MSC_TOKEN_MASK, token) | > + FIELD_PREP(MPAM_MSC_PROT_ID_MASK, MPAM_FB_PROTOCOL_ID), > + &pcc_shmem->command); > + > + writel_relaxed(msc_id, &payload->msc_id); > + writel_relaxed(0, &payload->flags); > + writel_relaxed(reg, &payload->reg_offset); > + writel_relaxed(val, &payload->value); > + > + return MPAM_WRITE_MSG_SIZE; > +} > + > +static int mpam_fb_send_request(struct mpam_pcc_chan *pcc_chan, u32 msc_id, > + u16 reg, u32 *result, int mpam_fb_command) > +{ > + unsigned int token = atomic_inc_return(&mpam_fb_token); > + struct acpi_pcct_ext_pcc_shared_memory *pcc_shmem; > + struct pcc_mbox_chan *chan; > + void __iomem *payload_ofs; > + u32 status; > + int ret; > + > + if (!pcc_chan) > + return -ENODEV; > + > + chan = pcc_chan->pcc_chan; > + > + guard(mutex)(&pcc_chan->pcc_chan_lock); > + > + switch (mpam_fb_command) { > + case MPAM_MSC_WRITE_CMD: > + ret = mpam_fb_build_write_message(msc_id, reg, *result, > + token, chan->shmem); > + break; > + case MPAM_MSC_READ_CMD: > + ret = mpam_fb_build_read_message(msc_id, reg, > + token, chan->shmem); > + break; > + case MPAM_PROTOCOL_VERSION: > + ret = mpam_fb_build_version_message(token, chan->shmem); > + break; > + } > + if (ret < 0) > + return ret; > + > + ret = mbox_send_message(chan->mchan, NULL); > + if (ret < 0) > + return ret; > + > + pcc_shmem = chan->shmem; > + payload_ofs = chan->shmem + sizeof(*pcc_shmem); > + status = readl(&pcc_shmem->command); > + if (FIELD_GET(MPAM_MSC_TOKEN_MASK, status) != token) > + return -ETIMEDOUT; > + > + ret = readl(payload_ofs + 0x0); > + if (ret < 0) { > + switch (ret) { > + case MPAM_FB_ERR_NOT_SUPPORTED: > + return -EOPNOTSUPP; > + case MPAM_FB_ERR_INVALID_PARAMETERS: > + return -EINVAL; > + case MPAM_FB_ERR_NOT_FOUND: > + return -ENOENT; > + case MPAM_FB_ERR_OUT_OF_RANGE: > + return -ERANGE; > + default: > + return -EINVAL; > + } > + } > + > + if (mpam_fb_command != MPAM_MSC_WRITE_CMD) > + *result = readl(payload_ofs + 0x4); > + > + return 0; > +} > + > +int mpam_fb_send_read_request(struct mpam_msc *msc, u16 reg, u32 *result) > +{ > + return mpam_fb_send_request(msc->pcc_chan, msc->mpam_fb_msc_id, > + reg, result, MPAM_MSC_READ_CMD); > +} > + > +int mpam_fb_send_write_request(struct mpam_msc *msc, u16 reg, u32 value) > +{ > + return mpam_fb_send_request(msc->pcc_chan, msc->mpam_fb_msc_id, > + reg, &value, MPAM_MSC_WRITE_CMD); > +} > + > +int mpam_fb_get_protocol_version(struct mpam_msc *msc) > +{ > + u32 version; > + int ret; > + > + ret = mpam_fb_send_request(msc->pcc_chan, 0, > + 0, &version, MPAM_PROTOCOL_VERSION); > + if (ret) > + return ret; > + > + return version; > +} > diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h > index 7b6e0df904f8..c3c4ddb4a561 100644 > --- a/drivers/resctrl/mpam_internal.h > +++ b/drivers/resctrl/mpam_internal.h > @@ -11,6 +11,7 @@ > #include > #include > #include > +#include > #include > #include > #include > @@ -57,6 +58,15 @@ struct mpam_garbage { > struct platform_device *pdev; > }; > > +struct mpam_pcc_chan { > + struct list_head pcc_chans; > + struct mbox_client pcc_cl; > + struct pcc_mbox_chan *pcc_chan; > + struct mutex pcc_chan_lock; /* only one message at a time */ > + int subspace_id; > + int refcount; > +}; > + > struct mpam_msc { > /* member of mpam_all_msc */ > struct list_head all_msc_list; > @@ -66,6 +76,8 @@ struct mpam_msc { > > /* Not modified after mpam_is_enabled() becomes true */ > enum mpam_msc_iface iface; > + struct mpam_pcc_chan *pcc_chan; > + int mpam_fb_msc_id; /* in its own name space */ > u32 nrdy_usec; > cpumask_t accessibility; > bool has_extd_esr; > @@ -501,6 +513,14 @@ static inline void mpam_resctrl_offline_cpu(unsigned int cpu) { } > static inline void mpam_resctrl_teardown_class(struct mpam_class *class) { } > #endif /* CONFIG_RESCTRL_FS */ > > +/* 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_get_protocol_version(struct mpam_msc *msc); > + > +#define PCC_TYPE3_MSG_PAYLOAD_OFS 0x10 > +#define MPAM_FB_MAX_MSG_SIZE (PCC_TYPE3_MSG_PAYLOAD_OFS + 4 * sizeof(u32)) > + > /* > * MPAM MSCs have the following register layout. See: > * Arm Memory System Resource Partitioning and Monitoring (MPAM) System > diff --git a/include/linux/arm_mpam.h b/include/linux/arm_mpam.h > index f92a36187a52..002f56e15362 100644 > --- a/include/linux/arm_mpam.h > +++ b/include/linux/arm_mpam.h > @@ -12,7 +12,7 @@ struct mpam_msc; > > enum mpam_msc_iface { > MPAM_IFACE_MMIO, /* a real MPAM MSC */ > - MPAM_IFACE_PCC, /* a fake MPAM MSC */ > + MPAM_IFACE_PCC, /* using the MPAM-Fb firmware redirection */ > }; > > enum mpam_class_types {