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 71429221546; Mon, 29 Sep 2025 17:45:00 +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=1759167901; cv=none; b=PAM8YRgsxcp3ubyin9wswekn8hPkuJmS20KLXj7BO4vunNR4mlSPN7eyLIcss7fOm2WG7danO3YEbUidlE2vFS4uBCBds2fqyCHXnAA8xZefnIwPo8C3+tv5wYC5UYZmJUcUnJp9lhk/n+uKKYln4Q1p5oeQeA79q5/hGD5rK/M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759167901; c=relaxed/simple; bh=DbJyopLs9gb7tcDqwcyS8ltGYv6IGcFf1Qf6xx98aBo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=uGSZrj3xhVyeGoNpxCkMJraMa70ydJ8u6FOwd6zmsFkG8EbcmrzzToZ59nP8cK0pdYP3S7ngpAqZjgF04oPRMQzsp6QHj8FaGqI73m5FV78cilBpR2/bGlV4TGXUJ3zZ6ZR1AfLtQtI1ZHDPcXQxE2ILf5lUOeIVL7aqwsdn4lE= 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; 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 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 A4F021CC4; Mon, 29 Sep 2025 10:44:51 -0700 (PDT) Received: from [10.1.197.69] (eglon.cambridge.arm.com [10.1.197.69]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8E5C33F59E; Mon, 29 Sep 2025 10:44:54 -0700 (PDT) Message-ID: <2672f409-7923-4b9b-9009-bb5815205e57@arm.com> Date: Mon, 29 Sep 2025 18:44:54 +0100 Precedence: bulk X-Mailing-List: linux-acpi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 12/29] arm_mpam: Add helpers for managing the locking around the mon_sel registers To: Ben Horgan , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-acpi@vger.kernel.org Cc: D Scott Phillips OS , carl@os.amperecomputing.com, lcherian@marvell.com, bobo.shaobowang@huawei.com, tan.shaopeng@fujitsu.com, baolin.wang@linux.alibaba.com, Jamie Iles , Xin Hao , peternewman@google.com, dfustini@baylibre.com, amitsinght@marvell.com, David Hildenbrand , Dave Martin , Koba Ko , Shanker Donthineni , fenghuay@nvidia.com, baisheng.gao@unisoc.com, Jonathan Cameron , Rob Herring , Rohit Mathew , Rafael Wysocki , Len Brown , Lorenzo Pieralisi , Hanjun Guo , Sudeep Holla , Catalin Marinas , Will Deacon , Greg Kroah-Hartman , Danilo Krummrich References: <20250910204309.20751-1-james.morse@arm.com> <20250910204309.20751-13-james.morse@arm.com> Content-Language: en-GB From: James Morse In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Hi Ben, On 11/09/2025 16:31, Ben Horgan wrote: > On 9/10/25 21:42, James Morse wrote: >> The MSC MON_SEL register needs to be accessed from hardirq for the overflow >> interrupt, and when taking an IPI to access these registers on platforms >> where MSC are not accesible from every CPU. This makes an irqsave >> spinlock the obvious lock to protect these registers. On systems with SCMI >> mailboxes it must be able to sleep, meaning a mutex must be used. The >> SCMI platforms can't support an overflow interrupt. >> >> Clearly these two can't exist for one MSC at the same time. >> >> Add helpers for the MON_SEL locking. The outer lock must be taken in a >> pre-emptible context before the inner lock can be taken. On systems with >> SCMI mailboxes where the MON_SEL accesses must sleep - the inner lock >> will fail to be 'taken' if the caller is unable to sleep. This will allow >> callers to fail without having to explicitly check the interface type of >> each MSC. >> diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h >> index 828ce93c95d5..4cc44d4e21c4 100644 >> --- a/drivers/resctrl/mpam_internal.h >> +++ b/drivers/resctrl/mpam_internal.h >> @@ -70,12 +70,17 @@ struct mpam_msc { >> >> /* >> * mon_sel_lock protects access to the MSC hardware registers that are >> - * affected by MPAMCFG_MON_SEL. >> + * affected by MPAMCFG_MON_SEL, and the mbwu_state. >> + * Access to mon_sel is needed from both process and interrupt contexts, >> + * but is complicated by firmware-backed platforms that can't make any >> + * access unless they can sleep. >> + * Always use the mpam_mon_sel_lock() helpers. >> + * Accessed to mon_sel need to be able to fail if they occur in the wrong >> + * context. >> * If needed, take msc->probe_lock first. >> */ >> - struct mutex outer_mon_sel_lock; >> - raw_spinlock_t inner_mon_sel_lock; >> - unsigned long inner_mon_sel_flags; >> + raw_spinlock_t _mon_sel_lock; >> + unsigned long _mon_sel_flags; >> > > These stale variables can be removed in the patch that introduced them, > outer_mon_sel_lock, inner_mon_sel_lock, inner_mon_sel_flags. Jonathan > has already pointed out the stale comment and paragraph in the commit > message. Yeah - I forgot to rewrite the commit message when I split this patch. I'll pull those earlier bits into the now:later patch that splits the locking up. Thanks, James