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From: Bjorn Helgaas <helgaas@kernel.org>
To: Zhangfei Gao <zhangfei.gao@linaro.org>
Cc: Joerg Roedel <joro@8bytes.org>,
	Bjorn Helgaas <bhelgaas@google.com>,
	Arnd Bergmann <arnd@arndb.de>,
	Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	Hanjun Guo <guohanjun@huawei.com>,
	Sudeep Holla <sudeep.holla@arm.com>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Len Brown <lenb@kernel.org>,
	jean-philippe <jean-philippe@linaro.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Herbert Xu <herbert@gondor.apana.org.au>,
	kenneth-lee-2012@foxmail.com, Wangzhou <wangzhou1@hisilicon.com>,
	linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org,
	iommu@lists.linux-foundation.org, linux-acpi@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, linux-pci@vger.kernel.org
Subject: Re: [PATCH 0/2] Introduce PCI_FIXUP_IOMMU
Date: Fri, 5 Jun 2020 18:19:09 -0500	[thread overview]
Message-ID: <20200605231909.GA1155454@bjorn-Precision-5520> (raw)
In-Reply-To: <779f4044-cf6a-b0d3-916f-0274450c07d3@linaro.org>

On Thu, Jun 04, 2020 at 09:33:07PM +0800, Zhangfei Gao wrote:
> On 2020/6/2 上午1:41, Bjorn Helgaas wrote:
> > On Thu, May 28, 2020 at 09:33:44AM +0200, Joerg Roedel wrote:
> > > On Wed, May 27, 2020 at 01:18:42PM -0500, Bjorn Helgaas wrote:
> > > > Is this slowdown significant?  We already iterate over every device
> > > > when applying PCI_FIXUP_FINAL quirks, so if we used the existing
> > > > PCI_FIXUP_FINAL, we wouldn't be adding a new loop.  We would only be
> > > > adding two more iterations to the loop in pci_do_fixups() that tries
> > > > to match quirks against the current device.  I doubt that would be a
> > > > measurable slowdown.
> > > I don't know how significant it is, but I remember people complaining
> > > about adding new PCI quirks because it takes too long for them to run
> > > them all. That was in the discussion about the quirk disabling ATS on
> > > AMD Stoney systems.
> > > 
> > > So it probably depends on how many PCI devices are in the system whether
> > > it causes any measureable slowdown.
> > I found this [1] from Paul Menzel, which was a slowdown caused by
> > quirk_usb_early_handoff().  I think the real problem is individual
> > quirks that take a long time.
> > 
> > The PCI_FIXUP_IOMMU things we're talking about should be fast, and of
> > course, they're only run for matching devices anyway.  So I'd rather
> > keep them as PCI_FIXUP_FINAL than add a whole new phase.
> > 
> Thanks Bjorn for taking time for this.
> If so, it would be much simpler.
> 
> +++ b/drivers/iommu/iommu.c
> @@ -2418,6 +2418,10 @@ int iommu_fwspec_init(struct device *dev, struct
> fwnode_handle *iommu_fwnode,
>         fwspec->iommu_fwnode = iommu_fwnode;
>         fwspec->ops = ops;
>         dev_iommu_fwspec_set(dev, fwspec);
> +
> +       if (dev_is_pci(dev))
> +               pci_fixup_device(pci_fixup_final, to_pci_dev(dev));
> +
> 
> Then pci_fixup_final will be called twice, the first in pci_bus_add_device.
> Here in iommu_fwspec_init is the second time, specifically for iommu_fwspec.
> Will send this when 5.8-rc1 is open.

Wait, this whole fixup approach seems wrong to me.  No matter how you
do the fixup, it's still a fixup, which means it requires ongoing
maintenance.  Surely we don't want to have to add the Vendor/Device ID
for every new AMBA device that comes along, do we?

Bjorn

  reply	other threads:[~2020-06-05 23:19 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-26 11:49 [PATCH 0/2] Introduce PCI_FIXUP_IOMMU Zhangfei Gao
2020-05-26 11:49 ` [PATCH 1/2] PCI: " Zhangfei Gao
2020-05-26 14:46   ` Christoph Hellwig
2020-05-26 15:09     ` Zhangfei Gao
2020-05-27  9:01       ` Greg Kroah-Hartman
2020-05-26 11:49 ` [PATCH 2/2] iommu: calling pci_fixup_iommu in iommu_fwspec_init Zhangfei Gao
2020-05-27  9:01   ` Greg Kroah-Hartman
2020-05-28  6:53     ` Zhangfei Gao
2020-05-27  9:00 ` [PATCH 0/2] Introduce PCI_FIXUP_IOMMU Greg Kroah-Hartman
2020-05-27  9:53   ` Arnd Bergmann
2020-05-27 13:51     ` Zhangfei Gao
2020-05-27 18:18 ` Bjorn Helgaas
2020-05-28  6:46   ` Zhangfei Gao
2020-05-28  7:33   ` Joerg Roedel
2020-06-01 17:41     ` Bjorn Helgaas
2020-06-04 13:33       ` Zhangfei Gao
2020-06-05 23:19         ` Bjorn Helgaas [this message]
2020-06-08  2:54           ` Zhangfei Gao
2020-06-08 16:41             ` Bjorn Helgaas
2020-06-09  4:01               ` Zhangfei Gao
2020-06-09  9:15                 ` Arnd Bergmann
2020-06-09 16:49                   ` Bjorn Helgaas
2020-06-11  2:54                     ` Zhangfei Gao
2020-06-11 13:44                       ` Bjorn Helgaas
2020-06-13 14:30                         ` Zhangfei Gao
2020-06-15 23:52                           ` Bjorn Helgaas
2020-06-19  2:26                             ` Zhangfei Gao
2020-06-23 15:04                               ` Bjorn Helgaas
2020-12-16 11:24                                 ` Zhou Wang
2020-12-17 20:38                                   ` Bjorn Helgaas
2020-06-22 11:55         ` Joerg Roedel
2020-06-23  7:48           ` Zhangfei Gao
2020-06-22 11:53       ` Joerg Roedel

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