From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-f53.google.com ([209.85.215.53]:36779 "EHLO mail-lf0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753560AbcL3Jqx (ORCPT ); Fri, 30 Dec 2016 04:46:53 -0500 Received: by mail-lf0-f53.google.com with SMTP id t196so234704841lff.3 for ; Fri, 30 Dec 2016 01:46:52 -0800 (PST) Subject: Re: [PATCH 1/2] arm64: dma_mapping: allow PCI host driver to limit DMA mask To: Nikita Yushchenko , Catalin Marinas , Will Deacon , Arnd Bergmann , linux-arm-kernel@lists.infradead.org, Simon Horman , Bjorn Helgaas , linux-pci@vger.kernel.org, linux-renesas-soc@vger.kernel.org References: <1483044304-2085-1-git-send-email-nikita.yoush@cogentembedded.com> Cc: artemi.ivanov@cogentembedded.com, linux-kernel@vger.kernel.org From: Sergei Shtylyov Message-ID: Date: Fri, 30 Dec 2016 12:46:49 +0300 MIME-Version: 1.0 In-Reply-To: <1483044304-2085-1-git-send-email-nikita.yoush@cogentembedded.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-renesas-soc-owner@vger.kernel.org List-ID: Hello! On 12/29/2016 11:45 PM, Nikita Yushchenko wrote: > It is possible that PCI device supports 64-bit DMA addressing, and thus > it's driver sets device's dma_mask to DMA_BIT_MASK(64), however PCI host Its. > bridge has limitations on inbound transactions addressing. Example of > such setup is NVME Isn't it called NVMe? > SSD device connected to RCAR PCIe controller. R=Car. > Previously there was attempt to handle this via bus notifier: after > driver is attached to PCI device, bridge driver gets notifier callback, > and resets dma_mask from there. However, this is racy: PCI device driver > could already allocate buffers and/or start i/o in probe routine. > In NVME case, i/o is started in workqueue context, and this race gives > "sometimes works, sometimes not" effect. > > Proper solution should make driver's dma_set_mask() call to fail if host > bridge can't support mask being set. > > This patch makes __swiotlb_dma_supported() to check mask being set for "To" not needed here. > PCI device against dma_mask of struct device corresponding to PCI host > bridge (one with name "pciXXXX:YY"), if that dma_mask is set. > > This is the least destructive approach: currently dma_mask of that device > object is not used anyhow, thus all existing setups will work as before, > and modification is required only in actually affected components - > driver of particular PCI host bridge, and dma_map_ops of particular > platform. > > Signed-off-by: Nikita Yushchenko > --- > arch/arm64/mm/dma-mapping.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c > index 290a84f..49645277 100644 > --- a/arch/arm64/mm/dma-mapping.c > +++ b/arch/arm64/mm/dma-mapping.c [...] > @@ -347,6 +348,16 @@ static int __swiotlb_get_sgtable(struct device *dev, struct sg_table *sgt, > > static int __swiotlb_dma_supported(struct device *hwdev, u64 mask) > { > +#ifdef CONFIG_PCI > + if (dev_is_pci(hwdev)) { > + struct pci_dev *pdev = to_pci_dev(hwdev); > + struct pci_host_bridge *br = pci_find_host_bridge(pdev->bus); > + > + if (br->dev.dma_mask && (*br->dev.dma_mask) && > + (mask & (*br->dev.dma_mask)) != mask) Hum, inner parens not necessary? [...] MBR, Sergei