From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B3AB041DDEF; Fri, 24 Jul 2026 09:55:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784886918; cv=none; b=ZyNfVWulOeMKYcFNkVUEqD5UX1byk7dDPID54kK9x0KNw2SBFx+c0n3ispjLdT89s/86xRwNkh58+D93kJA6qgtU+6MPhWrQrY9IPfbvKF64+EqkHJHfotEpyngd2y1kais/EVHJxp42Tsac+MbGLDxrRRPA9D52wtx5SzHtXAc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784886918; c=relaxed/simple; bh=3CO1hzoHhWqTEJ1ZZCA4ebSGEqB3ONFNpKIZN3ENoco=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=G3dte83/6f9kQZwU7ry9H2EVakrSsDx/v9hoD0/zDJ8VmqsO3KATxwBaltEdK14A0yrL2Iio+CfuW6FxWfOmsJItT/Zh8Zhofwhbb1TsxrVZXa4gwOMBC6v0YGferD5+5+3p/1/CkDjdcao7LeBGyGjZQWbhHEPN15pVeNPd8bU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Y3hMcaRQ; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Y3hMcaRQ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 88C7C1F00A3A; Fri, 24 Jul 2026 09:55:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784886910; bh=CZoacX15n1s/wdu2z1dTP72aFcV6AUwO1bgAXZEOsx8=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=Y3hMcaRQ6kJleShuEits1tOJawoutRF3Q9l30Ffi/RtBR9jVDKXluPTIHNObRWwHa wWDYCY2+fnIbz2DGP++hRmLiBR7AuGKejuEUXfJPNpknSASwec/HybTVieqqFkU5Bt 489c2vJyrJ56sQoLKPZxg/osv21akQoXoc20t24C/8lpJFc5Q/LU/c1H7wHtEiY5Nk 4rbyEXE3VFL1ZE64EVKm8pIx0fDsndrkLciA3KVq+SENUfgj5zyEqQB0Nl+uwJJuHr k2+xtwTu+YwVswYSQcnLGX03idKkKVvNf2mDlzD0c48AF8ZTeBJxIqzhXtKi4AjOTB pFrrI9Zw0n31g== Date: Fri, 24 Jul 2026 10:55:04 +0100 From: Sudeep Holla To: Andre Przywara Cc: Lorenzo Pieralisi , Hanjun Guo , Sudeep Holla , Catalin Marinas , Will Deacon , "Rafael J . Wysocki" , Len Brown , James Morse , Ben Horgan , Reinette Chatre , Fenghua Yu , 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 Subject: Re: [PATCH v4 08/10] arm_mpam: add MPAM-Fb MSC firmware access support Message-ID: <20260724-imposing-lurking-toucanet-cfe22c@sudeepholla> References: <20260723155454.1760823-1-andre.przywara@arm.com> <20260723155454.1760823-9-andre.przywara@arm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260723155454.1760823-9-andre.przywara@arm.com> On Thu, Jul 23, 2026 at 05:54:52PM +0200, 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 | 27 ++++- > drivers/resctrl/mpam_fb.c | 197 ++++++++++++++++++++++++++++++++ > drivers/resctrl/mpam_internal.h | 20 ++++ > include/linux/arm_mpam.h | 2 +- > 5 files changed, 240 insertions(+), 8 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 e2cb884eacf4..b8108ed4b32c 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)); > The above doesn't make any sense for PCC accesses, perhaps need to be pushed down ? > + 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)); > Ditto -- Regards, Sudeep