From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.kernel.org ([198.145.29.99]:41352 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965340AbdEWTop (ORCPT ); Tue, 23 May 2017 15:44:45 -0400 Date: Tue, 23 May 2017 14:44:44 -0500 From: Bjorn Helgaas To: Shawn Lin Cc: Bjorn Helgaas , linux-pci@vger.kernel.org, linux-rockchip@lists.infradead.org, Brian Norris , Jeffy Chen Subject: Re: [PATCH] PCI: rockchip: check link status when validating device Message-ID: <20170523194443.GD7241@bhelgaas-glaptop.roam.corp.google.com> References: <1495177107-203736-1-git-send-email-shawn.lin@rock-chips.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <1495177107-203736-1-git-send-email-shawn.lin@rock-chips.com> Sender: linux-pci-owner@vger.kernel.org List-ID: On Fri, May 19, 2017 at 02:58:27PM +0800, Shawn Lin wrote: > This patch checks the link status before reading and > writing configure space of devices attached to the RC. > If the link status is down, we shouldn't try to access > the devices. What bad things happen without this patch? It's racy to check the link status, then do the config access. The link might go down after we check but before we can perform the access. > Signed-off-by: Shawn Lin > --- > > drivers/pci/host/pcie-rockchip.c | 12 ++++++++++++ > 1 file changed, 12 insertions(+) > > diff --git a/drivers/pci/host/pcie-rockchip.c b/drivers/pci/host/pcie-rockchip.c > index 0e020b6..1e64227 100644 > --- a/drivers/pci/host/pcie-rockchip.c > +++ b/drivers/pci/host/pcie-rockchip.c > @@ -275,9 +275,21 @@ static void rockchip_pcie_update_txcredit_mui(struct rockchip_pcie *rockchip) > rockchip_pcie_write(rockchip, val, PCIE_CORE_TXCREDIT_CFG1); > } > > +static inline bool rockchip_pcie_link_up(struct rockchip_pcie *rockchip) > +{ > + return PCIE_LINK_UP(rockchip_pcie_read(rockchip, > + PCIE_CLIENT_BASIC_STATUS1)); > +} > + > static int rockchip_pcie_valid_device(struct rockchip_pcie *rockchip, > struct pci_bus *bus, int dev) > { > + /* do not access the devices if the link isn't completed */ > + if (bus->number != rockchip->root_bus_nr) { > + if (!rockchip_pcie_link_up(rockchip)) > + return 0; > + } > + > /* access only one slot on each root port */ > if (bus->number == rockchip->root_bus_nr && dev > 0) > return 0; > -- > 1.9.1 > >