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 AD69CC43458 for ; Wed, 1 Jul 2026 12:06:45 +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: Content-Type:In-Reply-To:From:References:CC:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=wb7A/TS/HEDvAZgwyCH1DqONn9Dswjv2acmk5jyqSNo=; b=zf5WDhJfAfQL8GQobJd4zMU1Hj 15YCoQDlVHjZ1gyVSJXBw0fzT9Qbsn5wD3rIdo1h+dXX5R2ilf6tC5DLoovUHAgFX1PBiIYceXYUC k+nTVS8JgXDLVl492u9NWgYV0Jwj15iYmbNXZZnBIYCnvxyDSFdNCHLTbtRRxsSKJAmspeiwHP1sb 8oT0KyXWMg2fYmhLzgc0VnQCSkoExKD5TCz99zoLRJe5CY47msunTAq9iwaihFlh/DsY9/i8231UD m+c+FC5IHmnvw2Z3Oj0uWWNtWePlyBP70TFeVRhXGK3Vv4M1RtnC6PYWoBZzrMGyeMrNg+QOV8nPL sDlx6uiA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wetiA-00000001kNJ-2p5D; Wed, 01 Jul 2026 12:06:38 +0000 Received: from canpmsgout10.his.huawei.com ([113.46.200.225]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1wetcz-00000001WgM-3zKn for linux-arm-kernel@lists.infradead.org; Wed, 01 Jul 2026 12:01:20 +0000 dkim-signature: v=1; a=rsa-sha256; d=huawei.com; s=dkim; c=relaxed/relaxed; q=dns/txt; h=From; bh=wb7A/TS/HEDvAZgwyCH1DqONn9Dswjv2acmk5jyqSNo=; b=3ahc3ltqmkkXN9QOuiqpU41Hl9c7g10bPEsmpLbdkxKl22rY8Ydsv3Y7DuF/IsXfToBelOvol G9z6KYaKaF1ZDJEg+drbNGABLUE41nf239pKGy6A898SbEduRuZUdGZMmCMTzDG3r1JMeIkSjv1 swsO0K9vl0hnPnhv2DueDpQ= Received: from mail.maildlp.com (unknown [172.19.163.200]) by canpmsgout10.his.huawei.com (SkyGuard) with ESMTPS id 4gqyzb4XVxz1K96Z; Wed, 1 Jul 2026 19:51:55 +0800 (CST) Received: from kwepemr200004.china.huawei.com (unknown [7.202.195.241]) by mail.maildlp.com (Postfix) with ESMTPS id 28B134055B; Wed, 1 Jul 2026 20:01:04 +0800 (CST) Received: from [10.67.121.62] (10.67.121.62) by kwepemr200004.china.huawei.com (7.202.195.241) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Wed, 1 Jul 2026 20:01:03 +0800 Message-ID: Date: Wed, 1 Jul 2026 20:01:02 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] ACPI: CPPC: add paired FFH feedback-counter read hook To: Beata Michalska CC: , , , , , , , , , , , , , , , , , , , , References: <20260410094145.4132082-1-zhangpengjie2@huawei.com> <20260410094145.4132082-2-zhangpengjie2@huawei.com> From: Pengjie Zhang In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.67.121.62] X-ClientProxiedBy: kwepems100001.china.huawei.com (7.221.188.238) To kwepemr200004.china.huawei.com (7.202.195.241) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260701_050118_624129_18F73758 X-CRM114-Status: GOOD ( 27.94 ) 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 Hi Beata, Thanks for taking the time to review this patch. Please see my inline comments below. On 6/30/2026 3:37 PM, Beata Michalska wrote: > Gonna be a bit picky with wording so do bear with me ... > > On Fri, Apr 10, 2026 at 05:41:44PM +0800, Pengjie Zhang wrote: >> cppc_get_perf_ctrs() reads the delivered and reference performance >> counters one at a time. >> >> Allow architectures to provide both FFH feedback counters in one >> operation when that either narrows the sampling window or avoids extra >> cross-CPU reads. Add a small FFH-specific hook for that case and fall >> back to the existing per-register reads when unsupported. >> >> Signed-off-by: Pengjie Zhang >> --- >> drivers/acpi/cppc_acpi.c | 58 ++++++++++++++++++++++++++++++++++++---- >> include/acpi/cppc_acpi.h | 7 +++++ >> 2 files changed, 60 insertions(+), 5 deletions(-) >> >> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c >> index 2e91c5a97761..7b3e8b0597dc 100644 >> --- a/drivers/acpi/cppc_acpi.c >> +++ b/drivers/acpi/cppc_acpi.c >> @@ -988,6 +988,23 @@ int __weak cpc_read_ffh(int cpunum, struct cpc_reg *reg, u64 *val) >> return -ENOTSUPP; >> } >> >> +/** >> + * cpc_read_ffh_fb_ctrs() - Read FFH feedback counters together >> + * @cpunum: CPU number to read > This reads bit awkward. Target CPU maybe ? >> + * @reg1: first CPPC register information >> + * @val1: place holder for first return value >> + * @reg2: second CPPC register information >> + * @val2: place holder for second return value >> + * >> + * Return: 0 for success and error code > 0 on success, error code otherwise ? Will update the wording as suggested. >> + */ >> +int __weak cpc_read_ffh_fb_ctrs(int cpunum, struct cpc_reg *reg1, >> + u64 *val1, struct cpc_reg *reg2, u64 *val2) >> +{ >> + return -EOPNOTSUPP; >> +} >> + >> + >> /** >> * cpc_write_ffh() - Write FFH register >> * @cpunum: CPU number to write >> @@ -1504,6 +1521,40 @@ bool cppc_perf_ctrs_in_pcc(void) >> } >> EXPORT_SYMBOL_GPL(cppc_perf_ctrs_in_pcc); >> >> +static int cppc_read_perf_fb_ctrs(int cpunum, >> + struct cpc_register_resource *delivered_reg, >> + struct cpc_register_resource *reference_reg, >> + u64 *delivered, u64 *reference) > The signature here differs from cpc_read_ffh_fb_ctrs. > It's not an issue but it might be good idea to stay consistent maybe ? > Also ... was about to suggest to stick to either perf_ctrs or feedback_ctrs > in naming but it seems the is no clear pattern withint the file > ... You're right about the mixed naming. I will use the _fb_ctrs suffix for all new functions in v2. >> +{ >> + int ret; >> + >> + /* >> + * For FFH feedback counters, try a paired read first to reduce >> + * sampling skew between delivered and reference counters. Fall >> + * back to the existing per-register reads if unsupported. >> + */ >> + if (CPC_IN_FFH(delivered_reg) && CPC_IN_FFH(reference_reg)) { >> + ret = cpc_read_ffh_fb_ctrs(cpunum, >> + &delivered_reg->cpc_entry.reg, delivered, >> + &reference_reg->cpc_entry.reg, reference); >> + if (!ret) >> + return 0; >> + >> + if (ret != -EOPNOTSUPP) >> + return ret; > Shouldn't this one be enough ? Don't think you need the first condition. right，I will drop the redundant if (!ret) check in v2 >> + } >> + >> + ret = cpc_read(cpunum, delivered_reg, delivered); >> + if (ret) >> + return ret; >> + >> + ret = cpc_read(cpunum, reference_reg, reference); >> + if (ret) >> + return ret; > As you are not doing anything with 'ret' this could just be: > ret = cpc_read(cpunum, delivered_reg, delivered); > if (ret) return ret; > return cpc_read(cpunum, reference_reg, reference); > > Though that's minor. Good catch, this is much cleaner. I will apply this change. Thanks again for the constructive feedback! Best regards,  Pengjie > > --- > BR > Beata >> + >> + return 0; >> +} >> + >> /** >> * cppc_get_perf_ctrs - Read a CPU's performance feedback counters. >> * @cpunum: CPU from which to read counters. >> @@ -1547,11 +1598,8 @@ int cppc_get_perf_ctrs(int cpunum, struct cppc_perf_fb_ctrs *perf_fb_ctrs) >> } >> } >> >> - ret = cpc_read(cpunum, delivered_reg, &delivered); >> - if (ret) >> - goto out_err; >> - >> - ret = cpc_read(cpunum, reference_reg, &reference); >> + ret = cppc_read_perf_fb_ctrs(cpunum, delivered_reg, reference_reg, >> + &delivered, &reference); >> if (ret) >> goto out_err; >> >> diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h >> index d1f02ceec4f9..006b42dbbd4b 100644 >> --- a/include/acpi/cppc_acpi.h >> +++ b/include/acpi/cppc_acpi.h >> @@ -172,6 +172,8 @@ extern int cppc_get_transition_latency(int cpu); >> extern bool cpc_ffh_supported(void); >> extern bool cpc_supported_by_cpu(void); >> extern int cpc_read_ffh(int cpunum, struct cpc_reg *reg, u64 *val); >> +extern int cpc_read_ffh_fb_ctrs(int cpu, struct cpc_reg *reg1, u64 *val1, >> + struct cpc_reg *reg2, u64 *val2); >> extern int cpc_write_ffh(int cpunum, struct cpc_reg *reg, u64 val); >> extern int cppc_get_epp_perf(int cpunum, u64 *epp_perf); >> extern int cppc_set_epp_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls, bool enable); >> @@ -246,6 +248,11 @@ static inline int cpc_read_ffh(int cpunum, struct cpc_reg *reg, u64 *val) >> { >> return -EOPNOTSUPP; >> } >> +static inline int cpc_read_ffh_fb_ctrs(int cpu, struct cpc_reg *reg1, u64 *val1, >> + struct cpc_reg *reg2, u64 *val2) >> +{ >> + return -EOPNOTSUPP; >> +} >> static inline int cpc_write_ffh(int cpunum, struct cpc_reg *reg, u64 val) >> { >> return -EOPNOTSUPP; >> -- >> 2.33.0 >>