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 X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B6257C47404 for ; Mon, 7 Oct 2019 12:27:46 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id 876DD2070B for ; Mon, 7 Oct 2019 12:27:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="sOAIg9Z9" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 876DD2070B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=JHAp0uD2ixdLUAhnVYU25lvRFoQQx6Lmiipq7R2dCI4=; b=sOAIg9Z9en6Zgi Gdl5DRTbHUWqduGOSCU3GSxELwS7tbnWzukbFkqEPbzFxXw4Xj41BoE94fwQqngnnmddDNUxLMeSR aqChhwsOtWWGUPLgqlPDrqft7n4XC4cTwr/1O2t7iUHpmyFnxznRZamTnbL6bNizX5DdX4tC+c6MN 56cxgZNLRu3wOIMz7IpyY6Z31+X7i5zz625GeKyKPX/GkqNzp8WxvqnCzP+/um/1o1jnBrtdrwiBu Ek1dtLq0IaVPYOPOwRMl28cMvkC6b7PAq/dusaJs1amklbdVyZ+sPDLXdibbz6hMbw3JZ6tOYnGdD S9P/WVR1xJVulI8Jch9w==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.2 #3 (Red Hat Linux)) id 1iHS77-000570-EG; Mon, 07 Oct 2019 12:27:45 +0000 Received: from verein.lst.de ([213.95.11.211]) by bombadil.infradead.org with esmtps (Exim 4.92.2 #3 (Red Hat Linux)) id 1iHS74-00056e-Cb for linux-nvme@lists.infradead.org; Mon, 07 Oct 2019 12:27:43 +0000 Received: by verein.lst.de (Postfix, from userid 2407) id 7D0AE68B20; Mon, 7 Oct 2019 14:27:38 +0200 (CEST) Date: Mon, 7 Oct 2019 14:27:38 +0200 From: Christoph Hellwig To: Ard Biesheuvel Subject: Re: [PATCH v3] nvme: retain split access workaround for capability reads Message-ID: <20191007122738.GA24804@lst.de> References: <20191007114253.30735-1-ard.biesheuvel@linaro.org> <20191007120721.GA21060@lst.de> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20191007_052742_571665_4DE4EC9E X-CRM114-Status: GOOD ( 12.97 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: sagi@grimberg.me, Ilias Apalodimas , linux-nvme@lists.infradead.org, axboe@fb.com, Keith Busch , Christoph Hellwig Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org On Mon, Oct 07, 2019 at 02:24:58PM +0200, Ard Biesheuvel wrote: > > If you interconnect doesn't support 8-byte MMIO read/write TLPs you > > have a much deeper problem, as this will break all drivers using > > readq/writeq. And we currently only have compile time detection for > > readq/writeq, not runtime so you'll have to invent a scheme if this > > works at all or not. > > Sure. But the practical reality is that the hardware in question > (including the Apple controller) worked perfectly fine until commit > 7fd8930f26be4 introduced a readq() call into a file that had > deliberately been switched to using lo_hi_readq() because readq() > doesn't work reliably for all hardware we would like it to support. > Theorizing about *why* readq() doesn't work reliably in which > particular case doesn't seem that useful to me, given how trivial the > fix is. My point here is that if it isn't the PCIe device that is broken like in the apple case, but your interconnect you have a problem that can't be fixed just in the nvme driver. We have tons of other drivers relying in readq/writeq working if it is available. You'll need to find a more general workaround, independent of the fact that we have a few NVMe controllers that always need this workaround. And at least for NVMe the spec specically allows split 32-bit access at least. _______________________________________________ Linux-nvme mailing list Linux-nvme@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-nvme