On 04/24/2013 12:58 AM, Takao Indoh wrote:
> This patch resets PCIe devices on boot to stop ongoing DMA. When
> "pci=pcie_reset_devices" is specified, a hot reset is triggered on each
> PCIe root port and downstream port to reset its downstream endpoint.
>
> Problem:
> This patch solves the problem that kdump can fail when intel_iommu=on is
> specified. When intel_iommu=on is specified, many dma-remapping errors
> occur in second kernel and it causes problems like driver error or PCI
> SERR, at last kdump fails. This problem is caused as follows.
> 1) Devices are working on first kernel.
> 2) Switch to second kernel(kdump kernel). The devices are still working
> and its DMA continues during this switch.
> 3) iommu is initialized during second kernel boot and ongoing DMA causes
> dma-remapping errors.
>
> Solution:
> All DMA transactions have to be stopped before iommu is initialized. By
> this patch devices are reset and in-flight DMA is stopped before
> pci_iommu_init.
>
> To invoke hot reset on an endpoint, its upstream link need to be reset.
> reset_pcie_devices() is called from fs_initcall_sync, and it finds root
> port/downstream port whose child is PCIe endpoint, and then reset link
> between them. If the endpoint is VGA device, it is skipped because the
> monitor blacks out if VGA controller is reset.
>
Couple questions wrt VGA device:
(1) Many graphics devices are multi-function, one function being VGA;
is the VGA always function 0, so this scan sees it first & doesn't
do a reset on that PCIe link? if the VGA is not function 0, won't
this logic break (will reset b/c function 0 is non-VGA graphics) ?
(2) I'm hearing VGA will soon not be the a required console; this logic
assumes it is, and why it isn't blanked.
Q: Should the filter be based on a device having a device-class of display ?
> Actually this is v8 patch but quite different from v7 and it's been so
> long since previous post, so I start over again.
Thanks for this re-start. I need to continue reviewing the rest.
Q: Why not force IOMMU off when re-booting a kexec kernel to perform a crash
dump? After the crash dump, the system is rebooting to previous (iommu=on) setting.
That logic, along w/your previous patch to disable the IOMMU if iommu=off
is set, would remove this (relatively slow) PCI init sequencing ?
> Previous post:
> [PATCH v7 0/5] Reset PCIe devices to address DMA problem on kdump
> https://lkml.org/lkml/2012/11/26/814
>
> Signed-off-by: Takao Indoh<indou.takao at jp.fujitsu.com>
> ---
> Documentation/kernel-parameters.txt | 2 +
> drivers/pci/pci.c | 103 +++++++++++++++++++++++++++++++++++
> 2 files changed, 105 insertions(+), 0 deletions(-)
>
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 4609e81..2a31ade 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -2250,6 +2250,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
> any pair of devices, possibly at the cost of
> reduced performance. This also guarantees
> that hot-added devices will work.
> + pcie_reset_devices Reset PCIe endpoint on boot by hot
> + reset
> cbiosize=nn[KMG] The fixed amount of bus space which is
> reserved for the CardBus bridge's IO window.
> The default value is 256 bytes.
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index b099e00..42385c9 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -3878,6 +3878,107 @@ void __weak pci_fixup_cardbus(struct pci_bus *bus)
> }
> EXPORT_SYMBOL(pci_fixup_cardbus);
>
> +/*
> + * Return true if dev is PCIe root port or downstream port whose child is PCIe
> + * endpoint except VGA device.
> + */
> +static int __init need_reset(struct pci_dev *dev)
> +{
> + struct pci_bus *subordinate;
> + struct pci_dev *child;
> +
> + if (!pci_is_pcie(dev) || !dev->subordinate ||
> + list_empty(&dev->subordinate->devices) ||
> + ((pci_pcie_type(dev) != PCI_EXP_TYPE_ROOT_PORT)&&
> + (pci_pcie_type(dev) != PCI_EXP_TYPE_DOWNSTREAM)))
> + return 0;
> +
> + subordinate = dev->subordinate;
> + list_for_each_entry(child,&subordinate->devices, bus_list) {
> + if ((pci_pcie_type(child) == PCI_EXP_TYPE_UPSTREAM) ||
> + (pci_pcie_type(child) == PCI_EXP_TYPE_PCI_BRIDGE) ||
> + ((child->class>> 16) == PCI_BASE_CLASS_DISPLAY))
> + /* Don't reset switch, bridge, VGA device */
> + return 0;
> + }
> +
> + return 1;
> +}
> +
> +static void __init save_config(struct pci_dev *dev)
> +{
> + struct pci_bus *subordinate;
> + struct pci_dev *child;
> +
> + if (!need_reset(dev))
> + return;
> +
> + subordinate = dev->subordinate;
> + list_for_each_entry(child,&subordinate->devices, bus_list) {
> + dev_info(&child->dev, "save state\n");
> + pci_save_state(child);
> + }
> +}
> +
> +static void __init restore_config(struct pci_dev *dev)
> +{
> + struct pci_bus *subordinate;
> + struct pci_dev *child;
> +
> + if (!need_reset(dev))
> + return;
> +
> + subordinate = dev->subordinate;
> + list_for_each_entry(child,&subordinate->devices, bus_list) {
> + dev_info(&child->dev, "restore state\n");
> + pci_restore_state(child);
> + }
> +}
> +
> +static void __init do_device_reset(struct pci_dev *dev)
> +{
> + u16 ctrl;
> +
> + if (!need_reset(dev))
> + return;
> +
> + dev_info(&dev->dev, "Reset Secondary bus\n");
> +
> + /* Assert Secondary Bus Reset */
> + pci_read_config_word(dev, PCI_BRIDGE_CONTROL,&ctrl);
> + ctrl |= PCI_BRIDGE_CTL_BUS_RESET;
> + pci_write_config_word(dev, PCI_BRIDGE_CONTROL, ctrl);
> +
> + msleep(2);
> +
> + /* De-assert Secondary Bus Reset */
> + ctrl&= ~PCI_BRIDGE_CTL_BUS_RESET;
> + pci_write_config_word(dev, PCI_BRIDGE_CONTROL, ctrl);
> +}
> +
> +static int __initdata pcie_reset_devices;
> +static int __init reset_pcie_devices(void)
> +{
> + struct pci_dev *dev = NULL;
> +
> + if (!pcie_reset_devices)
> + return 0;
> +
> + for_each_pci_dev(dev)
> + save_config(dev);
> +
> + for_each_pci_dev(dev)
> + do_device_reset(dev);
> +
> + msleep(1000);
> +
> + for_each_pci_dev(dev)
> + restore_config(dev);
> +
> + return 0;
> +}
> +fs_initcall_sync(reset_pcie_devices);
> +
> static int __init pci_setup(char *str)
> {
> while (str) {
> @@ -3920,6 +4021,8 @@ static int __init pci_setup(char *str)
> pcie_bus_config = PCIE_BUS_PEER2PEER;
> } else if (!strncmp(str, "pcie_scan_all", 13)) {
> pci_add_flags(PCI_SCAN_ALL_PCIE_DEVS);
> + } else if (!strncmp(str, "pcie_reset_devices", 18)) {
> + pcie_reset_devices = 1;
> } else {
> printk(KERN_ERR "PCI: Unknown option `%s'\n",
> str);
