From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id A5B87C982E6 for ; Mon, 21 Sep 2026 16:28:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=+0Q1c8+iWUmjCb/LFDx56zSUXvnrXb5ByHvCNbq3fbc=; b=hTgbxdiUrTNW7uncMUPjXRnKGW BePyHF1UooO8zUIs464t19JYm28iq94sYReY9qs+G6XlG6rHp5KQRT4qjKBkNaLZr3z+0IsmZ9lJg j5A3b4OBMa6W8rtiC4wH9/mvj/2vlWVNLvls4li1vgRfNwpXA/Fpjs2ysS0WJ8JtZHMkMgVu0vbFp wxegDEmMqPCN+u4G5dIMw8rFJrpcu6oSSinQLA0L3SvBWKeYHerSUYAXtJi6nFn2U+Alr7V6fsfKD SrVb8rgIAdW7dRv6EeL+Dy8zri17euA5LJny15EmKXbOLY4PHxi0JFjkHMW9qXoB2qI/mxDqTeJ6J /hiAazpQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1x8gsk-00000002ped-15CT; Mon, 21 Sep 2026 16:28:42 +0000 Received: from desiato.infradead.org ([2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1x8gsi-00000002pdh-2Ko6 for linux-arm-kernel@bombadil.infradead.org; Mon, 21 Sep 2026 16:28:40 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=Content-Transfer-Encoding:Content-Type :In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date:Message-ID: Sender:Reply-To:Content-ID:Content-Description; bh=+0Q1c8+iWUmjCb/LFDx56zSUXvnrXb5ByHvCNbq3fbc=; b=foEofhujVx6V/Lu2ic3k1dwIKP FMilKmbpIRs7BP2OmrjJ4fiC+ptIdYcZarv7QCaSzTqbmoy/G0y5n/kiYJVECOzPxsFHPeNj8PwQj gK63K+v9UfgrOOR7kR7BfnWwmsqPffIdPIMiQPvCSkqbCNccvZFKffzLiDTq2BJ7g2z9FB+NGR494 yrIV/wXzrAKxEb1DCcBkfGJefCmqek2IFZ35P3bGfdufMdqtDs1iuV2ZlSIHWedfMSfxkj5wx0JJ+ SErxk7JTI63vYFaAMPgWGZt7kh1rFMgT8QjQq15rSx1gNjA63JSvDBx1iJN2Oqk4sNgUg/qoYvozf DpM/d32g==; Received: from foss.arm.com ([217.140.110.172]) by desiato.infradead.org with esmtp (Exim 4.99.2 #2 (Red Hat Linux)) id 1x8gse-0000000CYlo-3BHm for linux-arm-kernel@lists.infradead.org; Mon, 21 Sep 2026 16:28:39 +0000 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 5EE0119F0; Mon, 21 Sep 2026 09:28:28 -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 1FD443F9A2; Mon, 21 Sep 2026 09:28:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1790008111; bh=m2dl8YTZY3DsOKp5evDCX+Sh9buB1ABpJyTpyMJd9O4=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=blHh5Wg1HCyYhZ47HleWhM7X3QjSNO2lfWc1seBLPiwZk09O2S8W1EGTbgtBxy52d hbH5ewugIHjHlpZBhD2voZtBkFGHzzzsMCYQaLmJYxh+xPeOfd7baIzFGQcItA6Une lUqYpsvXQStERXx2BCL+HoNehG6y80Ulvmb+lXNM= Message-ID: Date: Mon, 21 Sep 2026 17:28:27 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v10 12/14] arm_mpam: detect and enable MPAM-Fb PCC 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 , Lee Trager , Ritwick Sharma , Gavin Shan , linux-acpi@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <20260911112835.714162-1-andre.przywara@arm.com> <20260911112835.714162-13-andre.przywara@arm.com> <3e7bdafd-d6ea-422c-82ff-e278a17280ff@arm.com> Content-Language: en-US From: Ben Horgan In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260921_172837_236465_CE232E6B X-CRM114-Status: GOOD ( 35.22 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Andre, On 21/09/2026 17:09, Andre Przywara wrote: > Hi Ben, > > On 9/11/26 17:09, Ben Horgan wrote: >> 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 >>> Tested-by: Ritwick Sharma # on Arm AGI CPU >>> Reviewed-by: Jonathan Cameron >>> Tested-by: Srivathsa L Rao >>> Reviewed-by: Srivathsa L Rao >>> Reviewed-by: Gavin Shan >>> --- >>>   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 >>>   #include >>>   #include >>> +#include >>>   #include >>>   #include >>>   #include >>> +#include >>>   #include >>>   #include >>>   #include >>>   #include >>>   +#include >>> +#include >>> + >>>   #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); >>> + >>>       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; >> >> This looks like the change earlier in the series to drivers/acpi/arm64/mpam.c makes no functional >> effect unless the proposed spec changes are accepted; the default is msc->id. I'd just move the > > Yes, but it reduces churn, and more importantly, is more true to the MPAM-Fb spec, which says: > "The MSC identifiers are sequential and start from 0 for each agent which uses this protocol." > So this requires that we have per-channel IDs for the MSCs, that's why I think it's justified to > introduce this already now, even when it's somewhat redundant as the code stands now, as we always > assign the system-wide ID to it. > > I can of course move that out (and have that already on top of v9, internally), but wanted to check > this with you. I don't really mind. If Lorenzo/Sudeep are happy with doing the preparation work in drivers/acpi/arm64/mpam.c then I'm ok with it. It's currently a non-functional change but does make the expected path forward slightly clearer. > >> earlier drivers/acpi/arm64/mpam.c to your last patch and introduce this device_property_read_u32() >> their too (or a separate patch if it's easier for anyone). That way all but the last two patches can >> be considered for merging without knowing what's going to happen with the spec. > > Well, sure, though I think a separation of MPAM-FB MSC IDs and system-wide MSC IDs is inevitable, > regardless of which spec is changed and how the numbers are assigned, exactly. It seems so. Thanks, Ben > >> The struct msc property mpam_fb_msc_id is a bit long. Better as msc->fb_id? > > Sure, can shorten that. > > Cheers, > Andre. > >>>       } 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: >> >