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 DD7F2CD4F5E for ; Thu, 21 May 2026 08:25:58 +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:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=edsBSL+SaPE67HXzxXKqJpO41lDkEnVkc2jVW/R7AaQ=; b=jVlRsEtcoZQr+GulLX7bu0ATzD GmC7p7Yp/0wOiASyu/Zji9pGYXBrGgx0DA3l4O1J2y1RwujV628ImpVKZXIv3tXV/IxmtSqzPVZvG 10ciA9KVLkxuUfJ1E2e2jcNlD7M4w17p8HX2v/RKDWCyswWbYlEEyCkCZ4UEHWKi7QB4/EyfS23GI RuolBliXcfmCPneW/RuKLE1m0dlFbBsDRTf3hjQRSECBvnNS/MeHFzt1rZ1GYn5wg1/QVNxbni/mN 1QGAag99lo+4Dk2i+iHeoW3cOTiy8dViHNtyZLIbyyKekMEGDmOHMYwUVOv0xmFaI+NjXezOt42KV AiinIAFg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wPyj7-0000000787u-0fZe; Thu, 21 May 2026 08:25:57 +0000 Received: from verein.lst.de ([213.95.11.211]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1wPyj5-0000000785X-0DDU for linux-nvme@lists.infradead.org; Thu, 21 May 2026 08:25:56 +0000 Received: by verein.lst.de (Postfix, from userid 2407) id C179268BFE; Thu, 21 May 2026 10:25:49 +0200 (CEST) Date: Thu, 21 May 2026 10:25:49 +0200 From: Christoph Hellwig To: Keith Busch Cc: Chao Shi , linux-nvme@lists.infradead.org, Christoph Hellwig , Sagi Grimberg , Jens Axboe , Tatsuya Sasaki , Maurizio Lombardi , linux-kernel@vger.kernel.org, Sungwoo Kim , Dave Tian , Weidong Zhu Subject: Re: [PATCH v2] nvme: reserve a keep-alive admin tag for all transports Message-ID: <20260521082549.GA11208@lst.de> References: <20260515071248.2689513-1-coshi036@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260521_012555_248200_5B6D67FB X-CRM114-Status: GOOD ( 22.55 ) X-BeenThere: linux-nvme@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-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org On Wed, May 20, 2026 at 02:26:13PM -0600, Keith Busch wrote: > On Fri, May 15, 2026 at 03:12:48AM -0400, Chao Shi wrote: > > Per NVMe 2.0a section 5.27.1.12 and the transport binding wording, > > PCIe MAY support KATO. Reserve one admin tag on all transports so > > the host is ready when a controller accepts the feature. Fabrics > > keeps two, the second being for the connect command. > > > > A quirk-based approach was considered but no PCIe controller > > documented to declare KAS != 0 was found (two enterprise SSDs tested > > locally report KAS=0), so an allowlist has no entries today. > > I totally get it's optional for PCIe, but that also means it's the > host's option on whether it wants to use it, and there's no requirement > we have to. We just need the driver react correctly when someone tries > to do it. > > I am skeptical anyone would produce a PCIe device that supports it, but > let's say someone does: what is the use case motivating enabling this > optional feature in this driver? If it's just because the option is > there, then I think we can just reject the user command submitting the > feature for PCIe transports, like I earlier suggested. Requiring an > active command will just harm idle power states. I don't think that's quite the point. We'd have to add special filtering to fix the reproducer. Compared to that just reserving a tag and officially supporting the feature is much easier and a much better story.