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 EB42B3EAC8D for ; Wed, 15 Jul 2026 09:11:10 +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=1784106673; cv=none; b=LRQBlt3HAITXs+Zc9p2xoeNGyp4nNmL56P3UtzpxqqRKoXYpSnVRUwam63Wly3RSRnjHuQ1w4gwFIYG0nrEUAOZSfXoSeNvs8Yz/bhPUUv0GfBL2S8D99w2e4vWbGDiZBrc5VeFZ3f7wvqBHGsVJ1EOeIaJ6rWXA2rLiZwqV4ac= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784106673; c=relaxed/simple; bh=NWRGhRQrsMTVwpVRHjf73I+9DQBOHVtwuNXynKGyA/M=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ajDAyPJjINQv+vSGY7UELwu5VGVuV1GG1LSWC/QrGWvuhn44VlgvEZfBoxG7PQNgTMOlyC2uYlOAINjmJ03O0G1lkulgQZlwf/VkVBZo8wxxbxyYScZvaU72VQIsVnCZH5wr5YmKRFaxshUIo8w9GCEm8L3BNOOeJJpH+g4G+Pw= 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=VkCtGFX9; 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="VkCtGFX9" 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 1A4271477; Wed, 15 Jul 2026 02:11:06 -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 65C813F915; Wed, 15 Jul 2026 02:11:09 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1784106670; bh=NWRGhRQrsMTVwpVRHjf73I+9DQBOHVtwuNXynKGyA/M=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=VkCtGFX9fHLkn8ZF/ukOGPFLNQK99tA0c50s0cXnzxHb4NbVKWN2aIuEyJsrLh8Zv Pej5WNdfk3oQEXQoLM5RQrQknoOzPKHv/VQiJJyFXLwFuhubiEZTH435P95u8EHn9q ltN9Gp1L8Pln4FDaxgeXf3ixDNMgDqsQoqMqGnIM= Message-ID: <81b32767-442f-498a-bf85-d448b5cdece3@arm.com> Date: Wed, 15 Jul 2026 10:11:08 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Thunderbird Daily Subject: Re: [PATCH v1 03/11] arm_mpam: Set mpam_feat_msmon_mbwu_31counter when there are bandwidth counters To: "Shaopeng Tan (Fujitsu)" Cc: "james.morse@arm.com" , "reinette.chatre@intel.com" , "fenghuay@nvidia.com" , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "dave.martin@arm.com" , "andre.przywara@arm.com" References: <20260710115546.29644-4-ben.horgan@arm.com> Content-Language: en-US From: Ben Horgan In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Hi Shaopeng, On 7/15/26 07:34, Shaopeng Tan (Fujitsu) wrote: > Hello Ben, > >> If there are memory bandwidth counters then there are 31 bit counters even >> if there are also 44 bit counters or 63 bit counters. > > Although 31-bit counters are always exist, aren't they never used simultaneously with 44-bit or 63-bit counters? > If the `mpam_feat_msmon_mbwu_31counter` feature is set to always be enabled, could that potentially cause a bug? Sure, potentially, any change of meaning of a feature flag can be a source of confusion and so bugs but based on my analysis this patch causes no change of behaviour in the driver other than in the lines it changes. I do, however, think it's clearer to have feature bits just indicate whether the feature is present or not rather than adding extra meaning. In a mismatched system, a class may end up using 31 bit counters even if some of the RIS support long counters. Thanks, Ben > > Best regards, > Shaopeng TAN > > >> Set the 31 bit bandwidth counter feature bit whenever there are bandwidth >> counters. >> >> Fixes: fdc29a141d63 ("arm_mpam: Probe for long/lwd mbwu counters") >> Signed-off-by: Ben Horgan >> --- >>  drivers/resctrl/mpam_devices.c | 4 ++-- >>  1 file changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c >> index acfa9a4dc2fc..11b10c3bc334 100644 >> --- a/drivers/resctrl/mpam_devices.c >> +++ b/drivers/resctrl/mpam_devices.c >> @@ -930,9 +930,9 @@ static void mpam_ris_hw_probe(struct mpam_msc_ris *ris) >>                                                  mpam_set_feature(mpam_feat_msmon_mbwu_63counter, props); >>                                          else >>                                                  mpam_set_feature(mpam_feat_msmon_mbwu_44counter, props); >> -                               } else { >> -                                       mpam_set_feature(mpam_feat_msmon_mbwu_31counter, props); >>                                  } >> + >> +                               mpam_set_feature(mpam_feat_msmon_mbwu_31counter, props); >>                          } >>                  } >>          } >> -- >> 2.43.0 >>