From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932509AbdLOPt6 (ORCPT ); Fri, 15 Dec 2017 10:49:58 -0500 Received: from userp2130.oracle.com ([156.151.31.86]:46206 "EHLO userp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932405AbdLOPtz (ORCPT ); Fri, 15 Dec 2017 10:49:55 -0500 Subject: Re: [Xen-devel] [PATCH V3 1/2] Drivers/PCI: Export pcie_has_flr() interface To: Bjorn Helgaas , Christoph Hellwig Cc: jgross@suse.com, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, JBeulich@suse.com, bhelgaas@google.com, xen-devel@lists.xenproject.org, boris.ostrovsky@Oracle.COM, roger.pau@citrix.com References: <20171207222145.9769-1-Govinda.Tatti@Oracle.COM> <20171207222145.9769-2-Govinda.Tatti@Oracle.COM> <20171208202424.GC12367@bhelgaas-glaptop.roam.corp.google.com> <426eeeab-0dcd-8de3-9c5f-a166acf2c130@Oracle.COM> <20171212005919.GB30595@bhelgaas-glaptop.roam.corp.google.com> <49956aaf-5fd5-939d-5fc7-231ffdb98b70@Oracle.COM> <20171213212420.GH30595@bhelgaas-glaptop.roam.corp.google.com> From: Govinda Tatti Organization: Oracle Corporation Message-ID: Date: Fri, 15 Dec 2017 09:48:02 -0600 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0 MIME-Version: 1.0 In-Reply-To: <20171213212420.GH30595@bhelgaas-glaptop.roam.corp.google.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=8745 signatures=668648 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1711220000 definitions=main-1712150222 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Thanks Bjorn and Christophfor your response. Please see below for my comments. On 12/13/2017 3:24 PM, Bjorn Helgaas wrote: > [+cc Christoph] > > On Wed, Dec 13, 2017 at 02:46:57PM -0600, Govinda Tatti wrote: >>>>>> -static bool pcie_has_flr(struct pci_dev *dev) >>>>>> +bool pcie_has_flr(struct pci_dev *dev) >>>>>> { >>>>>> u32 cap; >>>>>> @@ -3882,6 +3882,7 @@ static bool pcie_has_flr(struct pci_dev *dev) >>>>>> pcie_capability_read_dword(dev, PCI_EXP_DEVCAP, &cap); >>>>>> return cap & PCI_EXP_DEVCAP_FLR; >>>>>> } >>>>>> +EXPORT_SYMBOL_GPL(pcie_has_flr); >>>>> I'd rather change pcie_flr() so you could *always* call it, and it >>>>> would return 0, -ENOTTY, or whatever, based on whether FLR is >>>>> supported. Is that feasible? >>>> Sure, I will add pcie_has_flr() logic inside pcie_flr() and return >>>> appropriate >>>> values as suggested by you. Do we still want to retain pcie_has_flr() and >>>> its usage inside pci.c?.Otherwise, I will remove it and do required cleanup. >>> If you can restructure the code and remove pcie_has_flr() while >>> retaining the existing behavior of its callers, that would be great. >> I checked the current usage of pcie_has_flr() and pcie_flr(). I have >> a couple >> of questions or need some clarification. >> >> 1. pcie_has_flr() usage inside pci_probe_reset_function(). >> >>    This function is only calling pcie_has_flr() but not pcie_flr(). >>    Rest of the code is trying to do specific type of reset except >> pcie_flr(). >> >>         rc = pci_dev_specific_reset(dev, 1); >>         if (rc != -ENOTTY) >>                 return rc; >>         if (pcie_has_flr(dev)) >>                 return 0; >>         rc = pci_af_flr(dev, 1); >>         if (rc != -ENOTTY) >>                 return rc; >> >>    In other-words, I can remove usage of pcie_has_flr() in all other places >>    in pci.c except in above function. > I think we should keep the EXPORT_SYMBOL_GPL() part of a60a2b73ba69 > ("PCI: Export pcie_flr()"), but revert the restructuring part. > > Prior to a60a2b73ba69, we had > > int pcie_flr(struct pci_dev *dev, int probe); > > like all the other reset methods. AFAICT, the addition of > pcie_has_flr() was to optimize the path slightly because when drivers > call pcie_flr(), they should already know that their hardware supports > FLR. But I don't think that optimization is worth the extra code > complexity. If we do need to optimize it, we can check this in the > core during enumeration and set PCI_DEV_FLAGS_NO_FLR_RESET > accordingly. > > Christoph, chime in if I'm missing something here. Not all code paths are aware of FLR capability and also, not using pcie_flr().  For example, arch/powerpc/platforms/powernv/eeh-powernv.c drivers/crypto/cavium/nitrox/nitrox_main.c drivers/net/ethernet/cavium/liquidio/octeon_mailbox.c So, we should consider one of these options. - set PCI_DEV_FLAGS_NO_FLR_RESET if it is not supported. - pcie_flr() should return if it is not supported If we modify pcie_flr() to return error codes, then we need to modify all existing modules that are calling this function. Please let me know your preference, so that I can move accordingly. Thanks. Cheers GOVINDA