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=-7.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_2 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 1C1E6C2BBD1 for ; Mon, 14 Sep 2020 23:28:08 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (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 C3BBF20936 for ; Mon, 14 Sep 2020 23:28:07 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="Qq94PY3E" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C3BBF20936 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:Mime-Version:References:In-Reply-To:Date:To:From: Subject:Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=gDlE+W/Y5oa5myAy5zgKn4GqzQwZkBBVuRNzxb2Vsos=; b=Qq94PY3E5/FxFxW5nPeG7aYL1 nOrk8XKp4AbytkCs76ADgXdEZZqrN94aff9CUFt1KdNtvuM6HxPcOtE1B91AyN6bjxOSqeRmeZrcD YkF2BrUmVK6bKq8PGyVQNrx+amtyT8UEGOSjoeEUY/r6dAgsmR74JabQE4kQp4uC8lkF8QDqElw3F D8jxjxRT0EKO2QSSPFsLFi6uYWS/HF3CV6sKLfd2MujNMJpRI2I/oQBjsbrcFDneu751waKPHfZtS zWUpGxS187aqAeewOr7QDfXnXkOeBeT/c6JQoJs1cTX899tWO/PJnh+SZQlYt5JNZpGUL+S14zlBy A8WU7NJKw==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kHxre-00013o-6K; Mon, 14 Sep 2020 23:26:26 +0000 Received: from kernel.crashing.org ([76.164.61.194]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kHxrX-000135-9y for linux-arm-kernel@lists.infradead.org; Mon, 14 Sep 2020 23:26:22 +0000 Received: from localhost (gate.crashing.org [63.228.1.57]) (authenticated bits=0) by kernel.crashing.org (8.14.7/8.14.7) with ESMTP id 08ENPwuf006195 (version=TLSv1/SSLv3 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Mon, 14 Sep 2020 18:26:01 -0500 Message-ID: <2b539df4c9ec703458e46da2fc879ee3b310b31c.camel@kernel.crashing.org> Subject: Re: [PATCH] arm64: Enable PCI write-combine resources under sysfs From: Benjamin Herrenschmidt To: Jason Gunthorpe Date: Tue, 15 Sep 2020 09:25:57 +1000 In-Reply-To: <20200914225740.GP904879@nvidia.com> References: <20200910171033.GG904879@nvidia.com> <44acc22377958a57c738f5139c5b5df2841c2544.camel@kernel.crashing.org> <20200910232938.GJ904879@nvidia.com> <3110e00a1f4df7b7359ba4f2b7f86a35aa47405e.camel@kernel.crashing.org> <20200911214225.hml2wbbq2rofn4re@amazon.com> <20200914141726.GA904879@nvidia.com> <20200914142406.k44zrnp2wdsandsp@amazon.com> <20200914143819.GC904879@nvidia.com> <375c478593945a416f3180c3773bcb5240d2e36c.camel@kernel.crashing.org> <1d6f2ceb8d3538c906a1fdb8cd3d4c74ccffa42e.camel@kernel.crashing.org> <20200914225740.GP904879@nvidia.com> X-Mailer: Evolution 3.28.5-0ubuntu0.18.04.2 Mime-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200914_192622_322172_F74CBD04 X-CRM114-Status: GOOD ( 22.02 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Lorenzo Pieralisi , Leon Romanovsky , linux-pci@vger.kernel.org, Bjorn Helgaas , catalin.marinas@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org, Clint Sbisa Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, 2020-09-14 at 19:57 -0300, Jason Gunthorpe wrote: > On Tue, Sep 15, 2020 at 08:00:27AM +1000, Benjamin Herrenschmidt wrote: > > On Tue, 2020-09-15 at 07:42 +1000, Benjamin Herrenschmidt wrote: > > > > > > > which is back to my original question, how do you do DMA using > > > > /sys/xx/resources? Why not use VFIO like everything else? > > > > > > Note: All this doesnt' change the fact that sys/xx/resources_wc > > > exists > > > for other archs and I see no reasons so far not to have it on ARM... > > > > Also... it looks like VFIO also doesn't provide a way to do WC yet > > unfortunately :-( > > Yes, but if the driving reason for this patch is because a VFIO user > like EFA DPDK is trying to work around VFIO limitations, then I'd say > the VFIO mmap should be amended, and not so much worring about sysfs. I don't think the two are exclusive. > While there is no reason for ARM to not show the sysfs, it really > should never be used. Modern kernels in secure boot don't even show > it, for instance. It's useful for random things, I've used it quite a bit in a previous life for things like in-lab hw testing etc... There's tooling out there, esp. in the more 'embedded' side of thing that uses this, I don't see a good reason not to provide the same level of functionality. So Lorenzo, imho, we should merge the patch. As for fixing VFIO, definitely something to revive. The main contention point was which "interface" to use to request write combine. Let's restart that conversation with the appropriate folks, the last I remember, the question was to figure out what interface to provide userspace for the functionality. Clint, do you want to drive this as well ? Cheers, Ben. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel