From: Bjorn Helgaas <helgaas@kernel.org>
To: Jon Derrick <jonathan.derrick@intel.com>
Cc: linux-pci@vger.kernel.org,
Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
Yinghai Lu <yinghai@kernel.org>
Subject: Re: [PATCH v2] PCI: Configure MPS on rescan
Date: Fri, 1 Feb 2019 16:54:27 -0600 [thread overview]
Message-ID: <20190201225427.GU229773@google.com> (raw)
In-Reply-To: <20181106201242.2862-1-jonathan.derrick@intel.com>
On Tue, Nov 06, 2018 at 01:12:42PM -0700, Jon Derrick wrote:
> During pci_rescan_bus(), we may encounter new buses and devices which
> don't have MPS set for compatibility. Using this path, newly discovered
> buses and devices would then require their MPS to be configured after
> driver attachment, which may be too late for drivers which do memory
> transactions on probe.
This definitely looks like something we need to do. Have you tripped
over an actual problem? If so, it might be interesting to include a
symptom here, e.g., Unsupported Request error for hot-added device, or
whatever it is.
Can you clarify the "would then require their MPS to be configured"
part? Is there some path where we *do* configure MPS after driver
attachment? Or is this just a way of saying that "if we don't
configure MPS *before* driver attachment, we would have to do it
after"?
I'm thinking we could simply say something like:
During pci_rescan_bus(), we may encounter new devices which haven't
had MPS configured. Their MPS must be configured before we make the
devices available for driver attachment by calling
pci_bus_add_devices().
> This additionally ensures that any pcie_bus_config kernel settings will
> be applied to the buses and devices discovered through this path prior
> to driver attachment.
>
> Signed-off-by: Jon Derrick <jonathan.derrick@intel.com>
> ---
> v1: https://patchwork.kernel.org/patch/10642019/
>
> drivers/pci/probe.c | 29 +++++++++++++++++++++++++++++
> 1 file changed, 29 insertions(+)
>
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index b1c05b5054a0..126cd426b6f2 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -3156,6 +3156,34 @@ unsigned int pci_rescan_bus_bridge_resize(struct pci_dev *bridge)
> return max;
> }
>
> +/*
> + * Walks the PCI/PCIe tree to find the first instance of a PCIe device and
> + * hands off the PCIe bus to pcie_bus_configure_settings to walk the rest.
> + */
> +static int pcie_rescan_bus_configure_settings(struct pci_dev *dev, void *data)
> +{
> + if (pci_is_pcie(dev)) {
> + struct pci_bus *child, *bus = dev->bus;
> +
> + list_for_each_entry(child, &bus->children, node)
> + pcie_bus_configure_settings(child);
It looks possible that this could call pcie_bus_configure_settings()
a second time for a device that we've already configured. For
example, it's legal to call pci_rescan_bus() on an arbitrary bus even
if there has been no hot-add event.
Is there something that prevents us from touching this
already-configured device? *Probably* we would configure it the same
way the second time, but a driver is likely already attached to it,
and we shouldn't do anything to it. Even if
pcie_bus_configure_settings() happens to be idempotent, that seems
like it would be hard to verify and keep true indefinitely.
Bjorn
> +
> + return 1;
> + }
> + return 0;
> +}
> +
> +/**
> + * pci_bus_configure_settings - Configure bus settings
> + * @bus: PCI/PCIE bus to configure
> + *
> + * Currently only configures PCIe bus settings related to MPS and MRRS.
> + */
> +static void pci_bus_configure_settings(struct pci_bus *bus)
> +{
> + pci_walk_bus(bus, pcie_rescan_bus_configure_settings, NULL);
> +}
> +
> /**
> * pci_rescan_bus - Scan a PCI bus for devices
> * @bus: PCI bus to scan
> @@ -3171,6 +3199,7 @@ unsigned int pci_rescan_bus(struct pci_bus *bus)
>
> max = pci_scan_child_bus(bus);
> pci_assign_unassigned_bus_resources(bus);
> + pci_bus_configure_settings(bus);
> pci_bus_add_devices(bus);
>
> return max;
> --
> 2.14.4
>
next prev parent reply other threads:[~2019-02-01 22:54 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-06 20:12 [PATCH v2] PCI: Configure MPS on rescan Jon Derrick
2019-02-01 22:54 ` Bjorn Helgaas [this message]
2019-02-01 23:18 ` Derrick, Jonathan
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