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 BA6AF43DA56; Wed, 29 Jul 2026 08:56:54 +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=1785315418; cv=none; b=Qyt3mAdLW0L0kHW8NZXil/2W0WYGtzlDnDZoABDxkwXBlt5bkBxUsYEwD1HpXMN9CFxvd/JPleiQAkCGgxJivLdSNnbaeaX+cl4bHPc7ris1eBx5KAdG/QxfWbMiLZJ0gDF2h45OrqQExGDLLNmvsZfVxmg4riTeKJmXOICvMsU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785315418; c=relaxed/simple; bh=FFQG9krjJGFnmWpDsjdCrknEsKfMtLYnE/mkAybCzLU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=J0A5tDA/Xt0LkjqepYDQcQf4SpBeGMvwtaKJmV6KW8rVju41f011MOS0VleBuRs3mtEhwWeCfMbklstsLZqt4acqUEQgdfVjERix9JcFcJwx0I1IkKMGNdnsPcOFhGThJURzPlApCdU9HFuMh3zNict2RWewZuq/h3cp140nD64= 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=JRIpnnog; 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="JRIpnnog" 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 8ADA2169C; Wed, 29 Jul 2026 01:56:42 -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 395D43F66F; Wed, 29 Jul 2026 01:56:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1785315406; bh=FFQG9krjJGFnmWpDsjdCrknEsKfMtLYnE/mkAybCzLU=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=JRIpnnoggdGCK+GZSYVy/wNCRrt3U1/ukf8GwB4W+6XhFvtLU5EBYPaL3+iPdSCzH cJge0UCICE6ZbczEO0nEzJ88xJX+lg4cmQIsBpnJaDtUq1I0nzUMU/4GeBexWLsJTm RD8XCpE6BT06p5HyXqhz3pdlb9CUGKkftJwRkawk= Message-ID: <07375e75-972e-43af-9588-dabb0e81443f@arm.com> Date: Wed, 29 Jul 2026 09:56:42 +0100 Precedence: bulk X-Mailing-List: linux-acpi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Thunderbird Daily Subject: Re: [PATCH v4 10/10] 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 , linux-acpi@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <20260723155454.1760823-1-andre.przywara@arm.com> <20260723155454.1760823-11-andre.przywara@arm.com> Content-Language: en-US From: Ben Horgan In-Reply-To: <20260723155454.1760823-11-andre.przywara@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Hi Andre, Just a couple of nits I spotted just now. On 7/23/26 16:54, 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 > --- > drivers/acpi/arm64/mpam.c | 6 +- > drivers/resctrl/mpam_devices.c | 127 ++++++++++++++++++++++++++++++++- > 2 files changed, 129 insertions(+), 4 deletions(-) > > diff --git a/drivers/acpi/arm64/mpam.c b/drivers/acpi/arm64/mpam.c > index 84963a20c3e7..ca9b8754ae5f 100644 > --- a/drivers/acpi/arm64/mpam.c > +++ b/drivers/acpi/arm64/mpam.c > @@ -220,8 +220,8 @@ static struct platform_device * __init acpi_mpam_parse_msc(struct acpi_mpam_msc_ > struct platform_device *pdev __free(platform_device_put) = > platform_device_alloc("mpam_msc", tbl_msc->identifier); > int next_res = 0, next_prop = 0, err; > - /* pcc, nrdy, affinity and a sentinel */ > - struct property_entry props[4] = { 0 }; > + /* pcc, msc-id, nrdy, affinity and a sentinel */ > + struct property_entry props[5] = { 0 }; > /* mmio, 2xirq, no sentinel. */ > struct resource res[3] = { 0 }; > struct acpi_device *companion; > @@ -256,6 +256,8 @@ static struct platform_device * __init acpi_mpam_parse_msc(struct acpi_mpam_msc_ > } else if (iface == MPAM_IFACE_PCC) { > props[next_prop++] = PROPERTY_ENTRY_U32("pcc-channel", > tbl_msc->base_address); > + props[next_prop++] = PROPERTY_ENTRY_U32("msc-id", > + tbl_msc->identifier); > } > > acpi_mpam_parse_irqs(pdev, tbl_msc, res, &next_res); > diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c > index fea3161ffbe9..fc4b5f87fbe9 100644 > --- a/drivers/resctrl/mpam_devices.c > +++ b/drivers/resctrl/mpam_devices.c > @@ -19,14 +19,19 @@ > #include > #include > #include > +#include > #include > #include > #include > +#include > #include > #include > #include > #include > > +#include > +#include > + > #include "mpam_internal.h" > > /* Values for the T241 errata workaround */ > @@ -49,6 +54,86 @@ 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); > + kfree(cur); > +} > + > +static struct mpam_pcc_chan *mpam_pcc_chan_get(struct device *dev, > + int subspace_id) > +{ > + struct mpam_pcc_chan *cur; > + int ret; > + > + 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.dev = dev; > + 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" from the PCC ACPI table. */ > + cur->pcc_cl.tx_tout = cur->pcc_chan->latency * 5; > + > + ret = devm_mutex_init(dev, &cur->pcc_chan_lock); > + if (ret) > + return ERR_PTR(ret); > + > + 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. > @@ -2201,6 +2286,8 @@ static void mpam_msc_drv_remove(struct platform_device *pdev) > { > struct mpam_msc *msc = platform_get_drvdata(pdev); > > + mpam_pcc_chan_put(msc->pcc_chan); > + > mutex_lock(&mpam_list_lock); > mpam_msc_destroy(msc); > mutex_unlock(&mpam_list_lock); > @@ -2211,7 +2298,7 @@ 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; > @@ -2259,7 +2346,8 @@ 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(&pdev->dev, "pcc-channel", > + &pcc_subspace_id)) > msc->iface = MPAM_IFACE_MMIO; > else > msc->iface = MPAM_IFACE_PCC; > @@ -2275,6 +2363,41 @@ 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 msc_id; > + int ret; > + > + if (device_property_read_u32(&pdev->dev, "msc-id", &msc_id)) { We have an existing local variable 'dev' we can use here... > + pr_err("missing MPAM-Fb MSC identifier\n"); > + return ERR_PTR(-EINVAL); > + } > + msc->mpam_fb_msc_id = msc_id; > + > + msc->pcc_chan = mpam_pcc_chan_get(&pdev->dev, pcc_subspace_id); and here. > + if (IS_ERR(msc->pcc_chan)) { > + pr_err("Failed to request MSC PCC channel\n"); > + return ERR_CAST(msc->pcc_chan); > + } > + > + if (msc->pcc_chan->pcc_chan->shmem_size < MPAM_FB_MAX_MSG_SIZE) { > + pr_err("MPAM-Fb PCC channel size too small.\n"); > + mpam_pcc_chan_put(msc->pcc_chan); > + return ERR_PTR(-ENOMEM); > + } > + ret = mpam_fb_get_protocol_version(msc); > + if (ret < 0) { > + pr_err("Cannot query MPAM-Fb protocol version.\n"); > + mpam_pcc_chan_put(msc->pcc_chan); > + > + /* ret is an MPAM-Fb error code, return a Linux one. */ > + return ERR_PTR(-EIO); > + } > + if ((ret >> 16) != 1) { We can use FIELD_GET() to make this check clearer and to populate the error message just below. > + pr_err("Incompatible MPAM-Fb protocol version %d.%d\n", > + ret >> 16, ret & 0xffff); > + mpam_pcc_chan_put(msc->pcc_chan); > + return ERR_PTR(-EINVAL); > + } > } else { > return ERR_PTR(-EINVAL); > } Thanks, Ben