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 93E6A105F7AF for ; Fri, 13 Mar 2026 14:48:22 +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: MIME-Version:References:In-Reply-To:Message-ID:Date:Subject:Cc:To:From: Reply-To:Content-Type:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=qdYl7O4q3KgRO/6x/vHQ3/Oisgb9kH7NyUT9boDvc74=; b=v91RJPYxkxL3KYe/xLCSdN7ryW OuO3vlKUoyJgIoEDgT4S7ddoB7ppfUFh/dpS0bkA7kR7BYSRCe2rL+Mh84gKdWmrWZCDGldpZPC9x TyXFktS58qEcdyDWafeZnkdPQS+NPwWRJNT6l3xNX9XUvnZL6NuQxpUmwxyE2NdF2loqkfIdcnDJ4 gZ/jHBoxwLQTPQzJJyQ+OBXTUSYoN4i9sVYx7LU5jYTXWIVdThWe1o1HfiVhObQUl9INErIwJEww2 e0Fdb15l3DYb6n48IA8J9Pajxetz0+HPgIAyLjZK+kWB6xEYWxXHYMTi5uBpp1YfkPkyXV0hzYzc/ T/ElxqrQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1w13oG-00000000Rhl-0LtL; Fri, 13 Mar 2026 14:48:16 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1w13o5-00000000RWg-1RQB for linux-arm-kernel@lists.infradead.org; Fri, 13 Mar 2026 14:48:08 +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 A813B2308; Fri, 13 Mar 2026 07:47:58 -0700 (PDT) Received: from e134344.cambridge.arm.com (e134344.arm.com [10.1.196.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id C120B3F7BD; Fri, 13 Mar 2026 07:48:00 -0700 (PDT) From: Ben Horgan To: ben.horgan@arm.com Cc: amitsinght@marvell.com, baisheng.gao@unisoc.com, baolin.wang@linux.alibaba.com, carl@os.amperecomputing.com, dave.martin@arm.com, david@kernel.org, dfustini@baylibre.com, fenghuay@nvidia.com, gshan@redhat.com, james.morse@arm.com, jonathan.cameron@huawei.com, kobak@nvidia.com, lcherian@marvell.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, peternewman@google.com, punit.agrawal@oss.qualcomm.com, quic_jiles@quicinc.com, reinette.chatre@intel.com, rohit.mathew@arm.com, scott@os.amperecomputing.com, sdonthineni@nvidia.com, tan.shaopeng@fujitsu.com, xhao@linux.alibaba.com, catalin.marinas@arm.com, will@kernel.org, corbet@lwn.net, maz@kernel.org, oupton@kernel.org, joey.gouly@arm.com, suzuki.poulose@arm.com, kvmarm@lists.linux.dev, zengheng4@huawei.com, linux-doc@vger.kernel.org, Dave Martin , Shaopeng Tan Subject: [PATCH v6 22/40] arm_mpam: resctrl: Convert to/from MPAMs fixed-point formats Date: Fri, 13 Mar 2026 14:45:59 +0000 Message-ID: <20260313144617.3420416-23-ben.horgan@arm.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260313144617.3420416-1-ben.horgan@arm.com> References: <20260313144617.3420416-1-ben.horgan@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260313_074805_481927_ED4E7590 X-CRM114-Status: GOOD ( 13.63 ) 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 From: Dave Martin MPAM uses a fixed-point formats for some hardware controls. Resctrl provides the bandwidth controls as a percentage. Add helpers to convert between these. Ensure bwa_wd is at most 16 to make it clear higher values have no meaning. Tested-by: Gavin Shan Tested-by: Shaopeng Tan Tested-by: Peter Newman Tested-by: Zeng Heng Tested-by: Punit Agrawal Reviewed-by: Zeng Heng Reviewed-by: Shaopeng Tan Reviewed-by: Jonathan Cameron Signed-off-by: Dave Martin Signed-off-by: James Morse Signed-off-by: Ben Horgan --- Changes since v2: Ensure bwa_wd is at most 16 (moved from patch 40: arm_mpam: Generate a configuration for min controls) Expand comments --- drivers/resctrl/mpam_devices.c | 7 +++++ drivers/resctrl/mpam_resctrl.c | 51 ++++++++++++++++++++++++++++++++++ 2 files changed, 58 insertions(+) diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c index 0e5e24ef60fe..0c97f7708722 100644 --- a/drivers/resctrl/mpam_devices.c +++ b/drivers/resctrl/mpam_devices.c @@ -713,6 +713,13 @@ static void mpam_ris_hw_probe(struct mpam_msc_ris *ris) mpam_set_feature(mpam_feat_mbw_part, props); props->bwa_wd = FIELD_GET(MPAMF_MBW_IDR_BWA_WD, mbw_features); + + /* + * The BWA_WD field can represent 0-63, but the control fields it + * describes have a maximum of 16 bits. + */ + props->bwa_wd = min(props->bwa_wd, 16); + if (props->bwa_wd && FIELD_GET(MPAMF_MBW_IDR_HAS_MAX, mbw_features)) mpam_set_feature(mpam_feat_mbw_max, props); diff --git a/drivers/resctrl/mpam_resctrl.c b/drivers/resctrl/mpam_resctrl.c index cab3e9ccb5c7..adaec522c1a1 100644 --- a/drivers/resctrl/mpam_resctrl.c +++ b/drivers/resctrl/mpam_resctrl.c @@ -10,6 +10,7 @@ #include #include #include +#include #include #include #include @@ -242,6 +243,56 @@ static bool cache_has_usable_cpor(struct mpam_class *class) return class->props.cpbm_wd <= 32; } +/* + * Each fixed-point hardware value architecturally represents a range + * of values: the full range 0% - 100% is split contiguously into + * (1 << cprops->bwa_wd) equal bands. + * + * Although the bwa_bwd fields have 6 bits the maximum valid value is 16 + * as it reports the width of fields that are at most 16 bits. When + * fewer than 16 bits are valid the least significant bits are + * ignored. The implied binary point is kept between bits 15 and 16 and + * so the valid bits are leftmost. + * + * See ARM IHI0099B.a "MPAM system component specification", Section 9.3, + * "The fixed-point fractional format" for more information. + * + * Find the nearest percentage value to the upper bound of the selected band: + */ +static u32 mbw_max_to_percent(u16 mbw_max, struct mpam_props *cprops) +{ + u32 val = mbw_max; + + val >>= 16 - cprops->bwa_wd; + val += 1; + val *= MAX_MBA_BW; + val = DIV_ROUND_CLOSEST(val, 1 << cprops->bwa_wd); + + return val; +} + +/* + * Find the band whose upper bound is closest to the specified percentage. + * + * A round-to-nearest policy is followed here as a balanced compromise + * between unexpected under-commit of the resource (where the total of + * a set of resource allocations after conversion is less than the + * expected total, due to rounding of the individual converted + * percentages) and over-commit (where the total of the converted + * allocations is greater than expected). + */ +static u16 percent_to_mbw_max(u8 pc, struct mpam_props *cprops) +{ + u32 val = pc; + + val <<= cprops->bwa_wd; + val = DIV_ROUND_CLOSEST(val, MAX_MBA_BW); + val = max(val, 1) - 1; + val <<= 16 - cprops->bwa_wd; + + return val; +} + /* Test whether we can export MPAM_CLASS_CACHE:{2,3}? */ static void mpam_resctrl_pick_caches(void) { -- 2.43.0