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=-5.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT autolearn=unavailable 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 B8CF8C04AB4 for ; Tue, 21 May 2019 13:15:30 +0000 (UTC) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org [140.211.169.12]) (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 97A0F20856 for ; Tue, 21 May 2019 13:15:30 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 97A0F20856 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from mail.linux-foundation.org (localhost [127.0.0.1]) by mail.linuxfoundation.org (Postfix) with ESMTP id 59B69C3E; Tue, 21 May 2019 13:15:30 +0000 (UTC) Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id AB191C03 for ; Tue, 21 May 2019 13:15:28 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from newverein.lst.de (verein.lst.de [213.95.11.211]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id 5A05287A for ; Tue, 21 May 2019 13:15:27 +0000 (UTC) Received: by newverein.lst.de (Postfix, from userid 2407) id 4C85168AFE; Tue, 21 May 2019 15:15:04 +0200 (CEST) Date: Tue, 21 May 2019 15:15:03 +0200 From: Christoph Hellwig To: Russell King - ARM Linux admin Subject: Re: [PATCH 1/2] dma-mapping: truncate dma masks to what dma_addr_t can hold Message-ID: <20190521131503.GA5258@lst.de> References: <20190521124729.23559-1-hch@lst.de> <20190521124729.23559-2-hch@lst.de> <20190521130436.bgt53bf7nshz62ip@shell.armlinux.org.uk> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20190521130436.bgt53bf7nshz62ip@shell.armlinux.org.uk> User-Agent: Mutt/1.5.17 (2007-11-01) Cc: linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org, Robin Murphy , Christoph Hellwig X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: iommu-bounces@lists.linux-foundation.org Errors-To: iommu-bounces@lists.linux-foundation.org On Tue, May 21, 2019 at 02:04:37PM +0100, Russell King - ARM Linux admin wrote: > So how does the driver negotiation for >32bit addresses work if we don't > fail for large masks? > > I'm thinking about all those PCI drivers that need DAC cycles for >32bit > addresses, such as e1000, which negotiate via (eg): > > /* there is a workaround being applied below that limits > * 64-bit DMA addresses to 64-bit hardware. There are some > * 32-bit adapters that Tx hang when given 64-bit DMA addresses > */ > pci_using_dac = 0; > if ((hw->bus_type == e1000_bus_type_pcix) && > !dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(64))) { > pci_using_dac = 1; > } else { > err = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(32)); > if (err) { > pr_err("No usable DMA config, aborting\n"); > goto err_dma; > } > } > > and similar. If we blindly trunate the 64-bit to 32-bit, aren't we > going to end up with PCI cards using DAC cycles to a host bridge that > do not support DAC cycles? In general PCI devices just use DAC cycles when they need it. I only know of about a handful of devices that need to negotiate their addressing mode, and those already use the proper API for that, which is dma_get_required_mask. The e1000 example is a good case of how the old API confused people. First it only sets the 64-bit mask for devices which can support it, which is good, but then it sets the NETIF_F_HIGHDMA flag only if we set a 64-bit mask, which is completely unrelated to the DMA mask, it just means the driver can handle sk_buff fragments that do not have a kernel mapping, which really is a driver and not a hardware issue. So what this driver really should do is something like: diff --git a/drivers/net/ethernet/intel/e1000/e1000_main.c b/drivers/net/ethernet/intel/e1000/e1000_main.c index 551de8c2fef2..d9236083da94 100644 --- a/drivers/net/ethernet/intel/e1000/e1000_main.c +++ b/drivers/net/ethernet/intel/e1000/e1000_main.c @@ -925,7 +925,7 @@ static int e1000_probe(struct pci_dev *pdev, const struct pci_device_id *ent) static int cards_found; static int global_quad_port_a; /* global ksp3 port a indication */ - int i, err, pci_using_dac; + int i, err; u16 eeprom_data = 0; u16 tmp = 0; u16 eeprom_apme_mask = E1000_EEPROM_APME; @@ -996,16 +996,11 @@ static int e1000_probe(struct pci_dev *pdev, const struct pci_device_id *ent) * 64-bit DMA addresses to 64-bit hardware. There are some * 32-bit adapters that Tx hang when given 64-bit DMA addresses */ - pci_using_dac = 0; - if ((hw->bus_type == e1000_bus_type_pcix) && - !dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(64))) { - pci_using_dac = 1; - } else { - err = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(32)); - if (err) { - pr_err("No usable DMA config, aborting\n"); - goto err_dma; - } + err = dma_set_mask_and_coherent(&pdev->dev, + DMA_BIT_MASK(hw->bus_type == e1000_bus_type_pcix ? 64 : 32)); + if (err) { + pr_err("No usable DMA config, aborting\n"); + goto err_dma; } netdev->netdev_ops = &e1000_netdev_ops; @@ -1047,19 +1042,15 @@ static int e1000_probe(struct pci_dev *pdev, const struct pci_device_id *ent) netdev->priv_flags |= IFF_SUPP_NOFCS; - netdev->features |= netdev->hw_features; + netdev->features |= netdev->hw_features | NETIF_F_HIGHDMA; netdev->hw_features |= (NETIF_F_RXCSUM | NETIF_F_RXALL | NETIF_F_RXFCS); - if (pci_using_dac) { - netdev->features |= NETIF_F_HIGHDMA; - netdev->vlan_features |= NETIF_F_HIGHDMA; - } - netdev->vlan_features |= (NETIF_F_TSO | NETIF_F_HW_CSUM | - NETIF_F_SG); + NETIF_F_SG | + NETIF_F_HIGHDMA); /* Do not set IFF_UNICAST_FLT for VMWare's 82545EM */ if (hw->device_id != E1000_DEV_ID_82545EM_COPPER || _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu