The patch below does not apply to the 4.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From ea401499e943c307e6d44af6c2b4e068643e7884 Mon Sep 17 00:00:00 2001
From: Lukas Wunner lukas@wunner.de Date: Sat, 31 Jul 2021 14:39:01 +0200 Subject: [PATCH] PCI: pciehp: Ignore Link Down/Up caused by error-induced Hot Reset
Stuart Hayes reports that an error handled by DPC at a Root Port results in pciehp gratuitously bringing down a subordinate hotplug port:
RP -- UP -- DP -- UP -- DP (hotplug) -- EP
pciehp brings the slot down because the Link to the Endpoint goes down. That is caused by a Hot Reset being propagated as a result of DPC. Per PCIe Base Spec 5.0, section 6.6.1 "Conventional Reset":
For a Switch, the following must cause a hot reset to be sent on all Downstream Ports: [...]
* The Data Link Layer of the Upstream Port reporting DL_Down status. In Switches that support Link speeds greater than 5.0 GT/s, the Upstream Port must direct the LTSSM of each Downstream Port to the Hot Reset state, but not hold the LTSSMs in that state. This permits each Downstream Port to begin Link training immediately after its hot reset completes. This behavior is recommended for all Switches.
* Receiving a hot reset on the Upstream Port.
Once DPC recovers, pcie_do_recovery() walks down the hierarchy and invokes pcie_portdrv_slot_reset() to restore each port's config space. At that point, a hotplug interrupt is signaled per PCIe Base Spec r5.0, section 6.7.3.4 "Software Notification of Hot-Plug Events":
If the Port is enabled for edge-triggered interrupt signaling using MSI or MSI-X, an interrupt message must be sent every time the logical AND of the following conditions transitions from FALSE to TRUE: [...]
* The Hot-Plug Interrupt Enable bit in the Slot Control register is set to 1b.
* At least one hot-plug event status bit in the Slot Status register and its associated enable bit in the Slot Control register are both set to 1b.
Prevent pciehp from gratuitously bringing down the slot by clearing the error-induced Data Link Layer State Changed event before restoring config space. Afterwards, check whether the link has unexpectedly failed to retrain and synthesize a DLLSC event if so.
Allow each pcie_port_service_driver (one of them being pciehp) to define a slot_reset callback and re-use the existing pm_iter() function to iterate over the callbacks.
Thereby, the Endpoint driver remains bound throughout error recovery and may restore the device to working state.
Surprise removal during error recovery is detected through a Presence Detect Changed event. The hotplug port is expected to not signal that event as a result of a Hot Reset.
The issue isn't DPC-specific, it also occurs when an error is handled by AER through aer_root_reset(). So while the issue was noticed only now, it's been around since 2006 when AER support was first introduced.
[bhelgaas: drop PCI_ERROR_RECOVERY Kconfig, split pm_iter() rename to preparatory patch] Link: https://lore.kernel.org/linux-pci/08c046b0-c9f2-3489-eeef-7e7aca435bb9@gmail... Fixes: 6c2b374d7485 ("PCI-Express AER implemetation: AER core and aerdriver") Link: https://lore.kernel.org/r/251f4edcc04c14f873ff1c967bc686169cd07d2d.162763818... Reported-by: Stuart Hayes stuart.w.hayes@gmail.com Tested-by: Stuart Hayes stuart.w.hayes@gmail.com Signed-off-by: Lukas Wunner lukas@wunner.de Signed-off-by: Bjorn Helgaas bhelgaas@google.com Cc: stable@vger.kernel.org # v2.6.19+: ba952824e6c1: PCI/portdrv: Report reset for frozen channel Cc: Keith Busch kbusch@kernel.org
diff --git a/drivers/pci/hotplug/pciehp.h b/drivers/pci/hotplug/pciehp.h index 69fd401691be..918dccbc74b6 100644 --- a/drivers/pci/hotplug/pciehp.h +++ b/drivers/pci/hotplug/pciehp.h @@ -189,6 +189,8 @@ int pciehp_get_attention_status(struct hotplug_slot *hotplug_slot, u8 *status); int pciehp_set_raw_indicator_status(struct hotplug_slot *h_slot, u8 status); int pciehp_get_raw_indicator_status(struct hotplug_slot *h_slot, u8 *status);
+int pciehp_slot_reset(struct pcie_device *dev); + static inline const char *slot_name(struct controller *ctrl) { return hotplug_slot_name(&ctrl->hotplug_slot); diff --git a/drivers/pci/hotplug/pciehp_core.c b/drivers/pci/hotplug/pciehp_core.c index ad3393930ecb..f34114d45259 100644 --- a/drivers/pci/hotplug/pciehp_core.c +++ b/drivers/pci/hotplug/pciehp_core.c @@ -351,6 +351,8 @@ static struct pcie_port_service_driver hpdriver_portdrv = { .runtime_suspend = pciehp_runtime_suspend, .runtime_resume = pciehp_runtime_resume, #endif /* PM */ + + .slot_reset = pciehp_slot_reset, };
int __init pcie_hp_init(void) diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c index 3024d7e85e6a..83a0fa119cae 100644 --- a/drivers/pci/hotplug/pciehp_hpc.c +++ b/drivers/pci/hotplug/pciehp_hpc.c @@ -862,6 +862,32 @@ void pcie_disable_interrupt(struct controller *ctrl) pcie_write_cmd(ctrl, 0, mask); }
+/** + * pciehp_slot_reset() - ignore link event caused by error-induced hot reset + * @dev: PCI Express port service device + * + * Called from pcie_portdrv_slot_reset() after AER or DPC initiated a reset + * further up in the hierarchy to recover from an error. The reset was + * propagated down to this hotplug port. Ignore the resulting link flap. + * If the link failed to retrain successfully, synthesize the ignored event. + * Surprise removal during reset is detected through Presence Detect Changed. + */ +int pciehp_slot_reset(struct pcie_device *dev) +{ + struct controller *ctrl = get_service_data(dev); + + if (ctrl->state != ON_STATE) + return 0; + + pcie_capability_write_word(dev->port, PCI_EXP_SLTSTA, + PCI_EXP_SLTSTA_DLLSC); + + if (!pciehp_check_link_active(ctrl)) + pciehp_request(ctrl, PCI_EXP_SLTSTA_DLLSC); + + return 0; +} + /* * pciehp has a 1:1 bus:slot relationship so we ultimately want a secondary * bus reset of the bridge, but at the same time we want to ensure that it is diff --git a/drivers/pci/pcie/portdrv.h b/drivers/pci/pcie/portdrv.h index 6126ee4676a7..41fe1ffd5907 100644 --- a/drivers/pci/pcie/portdrv.h +++ b/drivers/pci/pcie/portdrv.h @@ -85,6 +85,8 @@ struct pcie_port_service_driver { int (*runtime_suspend)(struct pcie_device *dev); int (*runtime_resume)(struct pcie_device *dev);
+ int (*slot_reset)(struct pcie_device *dev); + /* Device driver may resume normal operations */ void (*error_resume)(struct pci_dev *dev);
diff --git a/drivers/pci/pcie/portdrv_pci.c b/drivers/pci/pcie/portdrv_pci.c index c7ff1eea225a..1af74c3d9d5d 100644 --- a/drivers/pci/pcie/portdrv_pci.c +++ b/drivers/pci/pcie/portdrv_pci.c @@ -160,6 +160,9 @@ static pci_ers_result_t pcie_portdrv_error_detected(struct pci_dev *dev,
static pci_ers_result_t pcie_portdrv_slot_reset(struct pci_dev *dev) { + size_t off = offsetof(struct pcie_port_service_driver, slot_reset); + device_for_each_child(&dev->dev, &off, pcie_port_device_iter); + pci_restore_state(dev); pci_save_state(dev); return PCI_ERS_RESULT_RECOVERED;