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[175.34.8.244]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2d0aa4fb5f4sm503705ad.84.2026.08.03.23.36.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 03 Aug 2026 23:36:21 -0700 (PDT) Message-ID: Date: Tue, 4 Aug 2026 16:36:08 +1000 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7 09/11] 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 , Ben Horgan , Reinette Chatre , Fenghua Yu Cc: Jonathan Cameron , Srivathsa L Rao , Ganapatrao Kulkarni , Trilok Soni , Srinivas Ramana , Niyas Sait , Lee Trager , Ritwick Sharma , linux-acpi@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <20260731170324.2927758-1-andre.przywara@arm.com> <20260731170324.2927758-10-andre.przywara@arm.com> Content-Language: en-US From: Gavin Shan In-Reply-To: <20260731170324.2927758-10-andre.przywara@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Hi Andre, On 8/1/26 3:03 AM, 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 > (simple) SCMI message generation, for just the fields we need. > > [1] https://developer.arm.com/documentation/den0144/latest > > Signed-off-by: Andre Przywara > Reviewed-by: Jonathan Cameron > Tested-by: Ritwick Sharma > --- > drivers/resctrl/Makefile | 2 +- > drivers/resctrl/mpam_devices.c | 57 +++++++-- > drivers/resctrl/mpam_fb.c | 209 ++++++++++++++++++++++++++++++++ > drivers/resctrl/mpam_internal.h | 18 +++ > include/linux/arm_mpam.h | 2 +- > 5 files changed, 275 insertions(+), 13 deletions(-) > create mode 100644 drivers/resctrl/mpam_fb.c > [...] > diff --git a/drivers/resctrl/mpam_fb.c b/drivers/resctrl/mpam_fb.c > new file mode 100644 > index 000000000000..61a91c6cec0a > --- /dev/null > +++ b/drivers/resctrl/mpam_fb.c > @@ -0,0 +1,209 @@ > +// SPDX-License-Identifier: GPL-2.0 > +// Copyright (C) 2024-2026 Arm Ltd. > + > +#include > +#include > +#include > +#include > +#include > +#include > + > +#include > +#include > + > +#include "mpam_internal.h" > + > +#define MPAM_FB_PROTOCOL_ID 0x1a > + > +#define MPAM_PROTOCOL_VERSION_CMD 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) > + Why we're not using GENMASK_U32() since the operand the message is 32-bits dwords? :-) > +#define MPAM_FB_PROT_HEADER_LEN sizeof(u32) > + > +static atomic_t mpam_fb_token = ATOMIC_INIT(0); > + > +static void mpam_fb_build_version_message(unsigned int token, > + void __iomem *msg_buf) > +{ > + struct acpi_pcct_ext_pcc_shared_memory __iomem *pcc_shmem = msg_buf; > + > + /* .signature is filled by the platform */ > + writel_relaxed(PCC_CMD_COMPLETION_NOTIFY, &pcc_shmem->flags); > + writel_relaxed(MPAM_FB_PROT_HEADER_LEN, &pcc_shmem->length); > + writel_relaxed(MPAM_PROTOCOL_VERSION_CMD | > + FIELD_PREP(MPAM_MSC_TOKEN_MASK, token) | > + FIELD_PREP(MPAM_MSC_PROT_ID_MASK, MPAM_FB_PROTOCOL_ID), > + &pcc_shmem->command); > +} static inline void writel_relaxed(u32 value, volatile void __iomem *addr) { ...} The input value would be 'unsigned long', which is converted to 'u32'. If GENMASK_U32() is used to define MPAM_MSC_TOKEN_MASK and MPAM_MSC_PROT_ID_MASK, the unexpected conversion can be avoided. Thanks, Gavin