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 344C942BE80; Thu, 30 Jul 2026 12:28:23 +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=1785414505; cv=none; b=ItACkwzQ2QkXBsiG1fxasz0DY4qAyOD4iGDzSRRaM95roHCo4oW50X8qhtSc8CukHV9RkrG1Go+Ps/uc7XOKmn7jlz97Sfc283g0FhUk+kQNv4WptRRqI1Q5dEkvABwG4MBnmzzbuJc/V68rXCfb4UzFlwVxOWOZMY93SGloce8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785414505; c=relaxed/simple; bh=ce4amSfeO5ddQ3+gJrnw/HXGToqlKSsEg2RqxIiD9ok=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=HyFXiDDnClqawePwvPBjQ/TcIAFpDVqN8tkfenXWTWT7g2cSqA1reAl+lneaZO+J5lWvJUp5wbPObliGfJGq7mLgDsp4uj7F6DmKMa6+Ow2DEFJcpCv8w+cimirzp21oPHn6Bsne9UoP/rQZ1CZrd946sOYrm3agjuXJnkpKUMY= 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=tWXA7mGH; 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="tWXA7mGH" 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 49F2A1684; Thu, 30 Jul 2026 05:28:19 -0700 (PDT) Received: from [192.168.178.24] (usa-sjc-mx-foss1.foss.arm.com [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 2B7173F86F; Thu, 30 Jul 2026 05:28:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1785414503; bh=ce4amSfeO5ddQ3+gJrnw/HXGToqlKSsEg2RqxIiD9ok=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=tWXA7mGHifOfLkLmdMqruX2twXxjpZPtD4VSAJQZWg0GDE4zSBv6JCBirXzfDVC1k aeou9Z3ikQ1exLGecSvWgAChFXglXHr1oXW1vIHwNYEkfQL2KoTZmNQfcFSlLjfyx/ E+d2wcUBe25Q3CU74AvRFgsVMRBpQejhUOi6drWA= Message-ID: <158b744b-9edc-4bf0-8e7d-f8c00f90cf8b@arm.com> Date: Thu, 30 Jul 2026 14:28:19 +0200 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 v5 08/10] arm_mpam: add MPAM-Fb MSC firmware access support To: Ben Horgan , 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 , Lee Trager , linux-acpi@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <20260729134124.2506269-1-andre.przywara@arm.com> <20260729134124.2506269-9-andre.przywara@arm.com> <7e58cb7f-f789-4939-b35e-1aba5bbca53f@arm.com> Content-Language: en-GB From: Andre Przywara In-Reply-To: <7e58cb7f-f789-4939-b35e-1aba5bbca53f@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Hi, On 7/30/26 12:59, Ben Horgan wrote: > Hi Andre, > > On 7/29/26 14:41, 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 >> --- >> drivers/resctrl/Makefile | 2 +- >> drivers/resctrl/mpam_devices.c | 52 ++++++-- >> drivers/resctrl/mpam_fb.c | 214 ++++++++++++++++++++++++++++++++ >> drivers/resctrl/mpam_internal.h | 22 ++++ >> include/linux/arm_mpam.h | 2 +- >> 5 files changed, 279 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..dbe984241b0d >> --- /dev/null >> +++ b/drivers/resctrl/mpam_fb.c [ ... ] >> +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 __iomem *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; >> + >> + /* prune token to fit into the 10 bits inside the command register */ >> + token = FIELD_GET(MPAM_MSC_TOKEN_MASK, >> + FIELD_PREP(MPAM_MSC_TOKEN_MASK, token)); >> + >> + guard(mutex)(&pcc_chan->pcc_chan_lock); > > As sashiko pointed out (strangely on its comments for patch 10) it's best to use mutex_lock() and > mutex_unlock() in this function now that we have lots of gotos here. As per the guidance in > include/linux/cleanup.h. Ah, indeed, I didn't make it to the very end of this comment ;-) Fixed. Cheers, Andre >> + >> + switch (mpam_fb_command) { >> + case MPAM_MSC_WRITE_CMD: >> + mpam_fb_build_write_message(msc_id, reg, *result, >> + token, chan->shmem); >> + break; >> + case MPAM_MSC_READ_CMD: >> + mpam_fb_build_read_message(msc_id, reg, token, chan->shmem); >> + break; >> + case MPAM_PROTOCOL_VERSION_CMD: >> + mpam_fb_build_version_message(token, chan->shmem); >> + break; >> + default: >> + dev_err(pcc_chan->pcc_cl.dev, "unsupported MPAM-Fb command %d\n", >> + mpam_fb_command); >> + ret = -EINVAL; >> + goto out_err; >> + } >> + >> + ret = mbox_send_message(chan->mchan, NULL); >> + if (ret < 0) >> + goto out_err; >> + >> + 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) { >> + ret = -ETIMEDOUT; >> + >> + goto out_err; >> + } >> + >> + ret = readl(payload_ofs + 0x0); >> + if (ret < 0) { >> + switch (ret) { >> + case MPAM_FB_ERR_NOT_SUPPORTED: >> + ret = -EOPNOTSUPP; >> + break; >> + case MPAM_FB_ERR_INVALID_PARAMETERS: >> + ret = -EINVAL; >> + break; >> + case MPAM_FB_ERR_NOT_FOUND: >> + ret = -ENOENT; >> + break; >> + case MPAM_FB_ERR_OUT_OF_RANGE: >> + ret = -ERANGE; >> + break; >> + default: >> + ret = -EINVAL; >> + } >> + >> + goto out_err; >> + } >> + >> + if (mpam_fb_command != MPAM_MSC_WRITE_CMD) >> + *result = readl(payload_ofs + 0x4); >> + >> + return 0; >> + >> +out_err: >> + mpam_fb_disable_mpam(ret); >> + >> + return ret; >> +} >> + >> +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_CMD); >> + if (ret) >> + return ret; >> + >> + return version; >> +} >> diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h >> index 2b81b6b0bf4e..a2193e7df57c 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 */ >> + struct kref refcount; >> + int subspace_id; >> +}; >> + >> 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; >> @@ -484,6 +496,9 @@ extern u8 mpam_pmg_max; >> void mpam_enable(struct work_struct *work); >> void mpam_disable(struct work_struct *work); >> >> +/* helper function to call from outside mpam_devices.c */ >> +void mpam_fb_disable_mpam(int err); >> + >> /* Reset all the RIS in a class under cpus_read_lock() */ >> void mpam_reset_class_locked(struct mpam_class *class); >> >> @@ -511,6 +526,13 @@ 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 MPAM_FB_PROT_HEADER_LEN 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 { >