Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757166Ab3JKHai (ORCPT ); Fri, 11 Oct 2013 03:30:38 -0400 Received: from szxga01-in.huawei.com ([119.145.14.64]:17227 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755677Ab3JKHah (ORCPT ); Fri, 11 Oct 2013 03:30:37 -0400 Message-ID: <5257A882.1070809@huawei.com> Date: Fri, 11 Oct 2013 15:28:02 +0800 From: Yijing Wang User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:17.0) Gecko/20130801 Thunderbird/17.0.8 MIME-Version: 1.0 To: Gavin Shan CC: Benjamin Herrenschmidt , Bjorn Helgaas , "James E.J. Bottomley" , , , Hanjun Guo , Paul Mackerras , Subject: Re: [PATCH v2 3/6] powerpc/pci: use pci_is_pcie() to simplify code References: <1378367730-25996-1-git-send-email-wangyijing@huawei.com> <1378367730-25996-3-git-send-email-wangyijing@huawei.com> <20130906203035.GA27940@google.com> <1381470596.5630.61.camel@pasglop> <20131011061654.GA561@shangw.(null)> <52579BD6.40802@huawei.com> <20131011065329.GA5013@shangw.(null)> In-Reply-To: <20131011065329.GA5013@shangw.(null)> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.135.76.69] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3428 Lines: 106 On 2013/10/11 14:53, Gavin Shan wrote: > On Fri, Oct 11, 2013 at 02:33:58PM +0800, Yijing Wang wrote: >> On 2013/10/11 14:16, Gavin Shan wrote: >>> On Fri, Oct 11, 2013 at 04:49:56PM +1100, Benjamin Herrenschmidt wrote: >>>> On Fri, 2013-09-06 at 14:30 -0600, Bjorn Helgaas wrote: >>>>> On Thu, Sep 05, 2013 at 03:55:27PM +0800, Yijing Wang wrote: > > .../... > >>>>>> Use pci_is_pcie() to simplify code. >>>>>> diff --git a/arch/powerpc/kernel/eeh.c b/arch/powerpc/kernel/eeh.c >>>>>> index 55593ee..6ebbe54 100644 >>>>>> --- a/arch/powerpc/kernel/eeh.c >>>>>> +++ b/arch/powerpc/kernel/eeh.c >>>>>> @@ -189,8 +189,7 @@ static size_t eeh_gather_pci_data(struct eeh_dev *edev, char * buf, size_t len) >>>>>> } >>>>>> >>>>>> /* If PCI-E capable, dump PCI-E cap 10, and the AER */ >>>>>> - cap = pci_find_capability(dev, PCI_CAP_ID_EXP); >>>>>> - if (cap) { >>>>>> + if (pci_is_pcie(dev)) { >>>>>> n += scnprintf(buf+n, len-n, "pci-e cap10:\n"); >>>>>> printk(KERN_WARNING >>>>>> "EEH: PCI-E capabilities and status follow:\n"); >>>> >>>> So we remove reading of "cap", but slightly further down the code does: >>>> >>>> for (i=0; i<=8; i++) { >>>> eeh_ops->read_config(dn, cap+4*i, 4, &cfg); >>>> n += scnprintf(buf+n, len-n, "%02x:%x\n", 4*i, cfg); >>>> printk(KERN_WARNING "EEH: PCI-E %02x: %08x\n", i, cfg); >>>> } >>>> >>>> Which actually *uses* the value of "cap" ... oops :-) >>>> >>> >>> It's my fault and I should have looked into the changes more closely. >>> How about changing it like this: >>> >>> cap = pci_is_pcie(dev) ? pci_pcie_cap(dev) : >>> pci_find_capability(dev, PCI_CAP_ID_EXP); >>> if (cap) { >>> ... >>> } >>> >>> It would save some PCI-CFG access cycles for most cases :-) >> >> Hi Gavin, it's not your fault, it's my fault. :) >> >> Because pci_pcie_cap(dev) == dev->pcie_cap == pci_find_capability(dev, PCI_CAP_ID_EXP); >> >> so I think it's ok to use dev->pcie_cap instead of stale "cap". >> > > Yijing, There has one exception: dev->pcie_cap isn't updated yet. In my idea, dev->pcie_cap(here is pci_dev->pcie_cap) will update in set_pcie_port_type() function, and this function always be called after allocate pci device. We get pci_dev by eeh_dev_to_pci_dev(), I think pci_dev has been initialized completely. > This function has possibility to be invoked before that. However, > we don't have the binding (eeh device <-> PCI device) for the case. > So the piece of code shouldn't be running In PCI core, I knew pci_scan_device() pci_setup_device() set_pcie_port_type() pci_dev->pcie_cap = pci_find_capability(pdev, PCI_CAP_ID_EXP); In powerpc, I also found of_scan_pci_dev() of_create_pci_dev() set_pcie_port_type() pci_dev->pcie_cap = pci_find_capability(pdev, PCI_CAP_ID_EXP); > > However, it's a bit safer to have pci_find_capability(dev, PCI_CAP_ID_EXP) > as well even though we needn't it for 99.9% cases if you agree :-) I agree, this function is not the performance bottleneck, safety is more important. :) So if Bjorn and Benjamin think it's not safe, it's ok to drop it. :) Thanks! Yijing. > > Thanks, > Gavin > > > . > -- Thanks! Yijing -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/