From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (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 6B7C3320A0A; Thu, 18 Dec 2025 12:29:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766060951; cv=none; b=ImdCJlyAROIR3srFR7Q0heL0Oj9FkTVYqIowOgNsZ5WE9z8w/R+ME3TkaC0LobfmVJqEDrpluLj05H6aZ045GYn9VQYoeg8mAC2uF/Iby8ZKWjjgtySUAZWvWw6VALhbCCAgfv/nO/L0H3cN06mQ40eTwkDoM/CyFUB0SKNc9zQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766060951; c=relaxed/simple; bh=adds845lQRzFbwztriWqeWtBph+cSPN49gnHz9Vn/uA=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=n/DmuNIdB+KT7bocA0+gaPpDJTv7KpqBHz/QQyLD1T/zEFY4GV+5KoBZEdMHWT9fmNHt6E550oLda7rDFR0QPHXV3THSzHA7qV+mnEmOmlEmBGIEhsg8gVElcqVSWT4XsauTbiJWUnMs8n4mp6jN4tFsJno0q4QbzbFAz48359I= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=desiato.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=YxQGNVn8; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=desiato.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="YxQGNVn8" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=MIME-Version:Content-Type:References: In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=adds845lQRzFbwztriWqeWtBph+cSPN49gnHz9Vn/uA=; b=YxQGNVn86ggBcisbQCv52xMUG2 1Om8gf71IBlF5R09MYuZItNrVOwrZxnPXSyHDE7FdbAUOBDhRNP1854CIhtLet0aA4sINe3sOATG+ 04HLYyCez+eirGvswEDiPw0WALu4h86lYSR/KlbGT4GW0hr+5tRyUgPOHoUCeTS42gKt1a8BfFEqx tTXVJlucb6WPRXuuQ9I0umSb3MJQKrPqMGNGodZTv5/sruUjqi6ZrqN1bQKQtQaI5n4ViEt7aFtD/ VR160SM2015fP5XzGAwWCWJbB16/yzkCCiMyZk1Oh/wZzP0fdsYPtVxGnOzaOZc+q15b6ibX5giy4 zmITVEyA==; Received: from [172.31.31.148] (helo=u09cd745991455d.ant.amazon.com) by desiato.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1vWCGE-00000008kPV-0MlH; Thu, 18 Dec 2025 11:33:36 +0000 Message-ID: Subject: Re: [PATCH net-next v5 1/2] ptp: introduce Alibaba CIPU PHC driver From: David Woodhouse To: Jakub Kicinski , Wen Gu , Thomas =?ISO-8859-1?Q?Wei=DFschuh?= , Thomas Gleixner Cc: richardcochran@gmail.com, andrew+netdev@lunn.ch, davem@davemloft.net, edumazet@google.com, pabeni@redhat.com, xuanzhuo@linux.alibaba.com, dust.li@linux.alibaba.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Date: Thu, 18 Dec 2025 12:28:47 +0000 In-Reply-To: <20251105162429.37127978@kernel.org> References: <20251030121314.56729-1-guwen@linux.alibaba.com> <20251030121314.56729-2-guwen@linux.alibaba.com> <20251031165820.70353b68@kernel.org> <8a74f801-1de5-4a1d-adc7-66a91221485d@linux.alibaba.com> <20251105162429.37127978@kernel.org> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-9mlBANSO3VJCDFimpUOw" User-Agent: Evolution 3.52.3-0ubuntu1.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by desiato.infradead.org. See http://www.infradead.org/rpr.html --=-9mlBANSO3VJCDFimpUOw Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, 2025-11-05 at 16:24 -0800, Jakub Kicinski wrote: > On Wed, 5 Nov 2025 18:22:19 +0800 Wen Gu wrote: > > On 2025/11/1 07:58, Jakub Kicinski wrote: > > > On Thu, 30 Oct 2025 20:13:13 +0800 Wen Gu wrote:=C2=A0=20 > > > > This adds a driver for Alibaba CIPU PTP clock. The CIPU, an underly= ing > > > > infrastructure of Alibaba Cloud, synchronizes time with atomic cloc= ks > > > > via the network and provides microsecond or sub-microsecond precisi= on > > > > timestamps for VMs and bare metals on cloud. > > > >=20 > > > > User space processes, such as chrony, running in VMs or on bare met= als > > > > can get the high precision time through the PTP device exposed by t= his > > > > driver.=C2=A0=20 > > >=20 > > > As mentioned on previous revisions this is a pure clock device which = has > > > nothing to do with networking and PTP.=C2=A0=20 > >=20 > > I don't quite agree that this has nothing to do with PTP. > >=20 > > What is the difference between this CIPU PTP driver and other PTP drive= rs > > under drivers/ptp? such as ptp_s390, ptp_vmw, ptp_pch, and others. Most= of > > these PTP drivers do not directly involve IEEE 1588 or networking as we= ll. >=20 > We can't delete existing drivers. It used to be far less annoying > until every cloud vendor under the sun decided to hack up their own > implementation of something as simple as the clock. Heh. In my defence, I hacked up a new one because none of the existing options (including the KVM abomination) were any use. None of them allow guests to rely on accurate time across live migration. VMClock is designed specifically to solve that problem. It's now published at https://uapi-group.org/specifications/specs/vmclock/ and although the primary target is virtual machines, it discusses how it could be used to build a hardware implementation using PCIe PTM. As well as obviously implementing it in $DAYJOB, we added it to QEMU. Although it *can* be used as a PHC providing a paired TAI timestamp, it actually provides a y=3Dmx+c relationship between the CPU counter (e.g. TSC) and real time, not just a timestamp at a given point in time. I'd like to integrate it as a first-class citizen in kernel timekeeping, so that the kernel can directly both consume it, *and* export the kernel's CLOCK_REALTIME to KVM guests. I don't care what happens to the legacy snapshot-only ones though; those can all go away as far as I'm concerned. I'd suggest that now it's possible to do it *right*, there shouldn't be any *more* of the legacy ones. Having said that, it does seem rather harsh to refuse to accept this one when there are so many other examples already in the tree. I'd suggest that we accept it and then it can be moved to the new setup, whatever that is, along with the other legacy snapshot-only PHCs. --=-9mlBANSO3VJCDFimpUOw Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCD9Aw ggSOMIIDdqADAgECAhAOmiw0ECVD4cWj5DqVrT9PMA0GCSqGSIb3DQEBCwUAMGUxCzAJBgNVBAYT AlVTMRUwEwYDVQQKEwxEaWdpQ2VydCBJbmMxGTAXBgNVBAsTEHd3dy5kaWdpY2VydC5jb20xJDAi BgNVBAMTG0RpZ2lDZXJ0IEFzc3VyZWQgSUQgUm9vdCBDQTAeFw0yNDAxMzAwMDAwMDBaFw0zMTEx MDkyMzU5NTlaMEExCzAJBgNVBAYTAkFVMRAwDgYDVQQKEwdWZXJva2V5MSAwHgYDVQQDExdWZXJv a2V5IFNlY3VyZSBFbWFpbCBHMjCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAMjvgLKj jfhCFqxYyRiW8g3cNFAvltDbK5AzcOaR7yVzVGadr4YcCVxjKrEJOgi7WEOH8rUgCNB5cTD8N/Et GfZI+LGqSv0YtNa54T9D1AWJy08ZKkWvfGGIXN9UFAPMJ6OLLH/UUEgFa+7KlrEvMUupDFGnnR06 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