From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) (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 DA2921DF248 for ; Thu, 21 May 2026 08:26:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=213.95.11.211 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779351963; cv=none; b=Ll1wXOo+Clo54r+iH2qCbsduCHkDXB6mygfmTQoTzZiR4pkLHAQRg9B1ooyd+2VsWQF3vCR+w1VvnnrzQpKQ3B+//QkmnwEL4qilNGxmffKQpqILax4xTRxbuZrfDgDsmCCJNcOBo/AbUdPyxgZoxzacsav1wlUsrtYlEUobuMo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779351963; c=relaxed/simple; bh=ayvWvUIWHNwsgyCxgq+wSSlrvJpc2d/9mybsjAdf+uY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Si7aVqa5yMSxGt9xVIwYrOocLF8lM5bIB0mpKBB9eE4dA99gPOpo2Y2iS/VlIuLwAa11Rr4F6+PxBON5EhWsCibsM1mjw34D34c8KaA+HXXDVlPXBAmm7V6/chEJfYWbziv19u8oDRbHZu0JeKfYEi/VB7J19D3Bxw2dWqPQB9E= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=lst.de; spf=pass smtp.mailfrom=lst.de; arc=none smtp.client-ip=213.95.11.211 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=lst.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=lst.de 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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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) 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.