Downstream Port Containment (PCIe Base Spec, sec. 6.2.10) disables the link upon an error and attempts to re-enable it when instructed by the DPC driver. A slot which is both DPC- and hotplug-capable is currently brought down by pciehp once DPC is triggered (due to the link change) and brought up on successful recovery. That's undesirable, the slot should remain up so that the hotplugged device remains bound to its driver. DPC notifies the driver of the error and of successful recovery in pcie_do_recovery() and the driver may then restore the device to working state. Moreover, Sinan points out that turning off slot power by pciehp may foil recovery by DPC: Power off/on is a cold reset concurrently to DPC's warm reset. Sathyanarayanan reports extended delays or failure in link retraining by DPC if pciehp brings down the slot. Fix by detecting whether a Link Down event is caused by DPC and awaiting recovery if so. On successful recovery, ignore both the Link Down and the subsequent Link Up event. Afterwards, check whether the link is down to detect surprise-removal or another DPC event immediately after DPC recovery. Ensure that the corresponding DLLSC event is not ignored by synthesizing it and invoking irq_wake_thread() to trigger a re-run of pciehp_ist(). The IRQ threads of the hotplug and DPC drivers, pciehp_ist() and dpc_handler(), race against each other. If pciehp is faster than DPC, it will wait until DPC recovery completes. Recovery consists of two steps: The first step (waiting for link disablement) is recognizable by pciehp through a set DPC Trigger Status bit. The second step (waiting for link retraining) is recognizable through a newly introduced PCI_DPC_RECOVERING flag. If DPC is faster than pciehp, neither of the two flags will be set and pciehp may glean the recovery status from the new PCI_DPC_RECOVERED flag. The flag is zero if DPC didn't occur at all, hence DLLSC events are not ignored by default. pciehp waits up to 4 seconds before assuming that DPC recovery failed and bringing down the slot. This timeout is not taken from the spec (it doesn't mandate one) but based on a report from Yicong Yang that DPC may take a bit more than 3 seconds on HiSilicon's Kunpeng platform. The timeout is necessary because the DPC Trigger Status bit may never clear: On Root Ports which support RP Extensions for DPC, the DPC driver polls the DPC RP Busy bit for up to 1 second before giving up on DPC recovery. Without the timeout, pciehp would then wait indefinitely for DPC to complete. This commit draws inspiration from previous attempts to synchronize DPC with pciehp: By Sinan Kaya, August 2018: https://lore.kernel.org/linux-pci/20180818065126.77912-1-okaya@xxxxxxxxxx/ By Ethan Zhao, October 2020: https://lore.kernel.org/linux-pci/20201007113158.48933-1-haifeng.zhao@xxxxxxxxx/ By Kuppuswamy Sathyanarayanan, March 2021: https://lore.kernel.org/linux-pci/59cb30f5e5ac6d65427ceaadf1012b2ba8dbf66c.1615606143.git.sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx/ Reported-by: Sinan Kaya <okaya@xxxxxxxxxx> Reported-by: Ethan Zhao <haifeng.zhao@xxxxxxxxx> Reported-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx> Tested-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx> Tested-by: Yicong Yang <yangyicong@xxxxxxxxxxxxx> Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx> Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx> Cc: Dan Williams <dan.j.williams@xxxxxxxxx> Cc: Ashok Raj <ashok.raj@xxxxxxxxx> Cc: Keith Busch <kbusch@xxxxxxxxxx> --- drivers/pci/hotplug/pciehp_hpc.c | 36 ++++++++++++++++ drivers/pci/pci.h | 4 ++ drivers/pci/pcie/dpc.c | 74 +++++++++++++++++++++++++++++--- 3 files changed, 109 insertions(+), 5 deletions(-) diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c index fb3840e222ad..9d06939736c0 100644 --- a/drivers/pci/hotplug/pciehp_hpc.c +++ b/drivers/pci/hotplug/pciehp_hpc.c @@ -563,6 +563,32 @@ void pciehp_power_off_slot(struct controller *ctrl) PCI_EXP_SLTCTL_PWR_OFF); } +static void pciehp_ignore_dpc_link_change(struct controller *ctrl, + struct pci_dev *pdev, int irq) +{ + /* + * Ignore link changes which occurred while waiting for DPC recovery. + * Could be several if DPC triggered multiple times consecutively. + */ + synchronize_hardirq(irq); + atomic_and(~PCI_EXP_SLTSTA_DLLSC, &ctrl->pending_events); + if (pciehp_poll_mode) + pcie_capability_write_word(pdev, PCI_EXP_SLTSTA, + PCI_EXP_SLTSTA_DLLSC); + ctrl_info(ctrl, "Slot(%s): Link Down/Up ignored (recovered by DPC)\n", + slot_name(ctrl)); + + /* + * If the link is unexpectedly down after successful recovery, + * the corresponding link change may have been ignored above. + * Synthesize it to ensure that it is acted on. + */ + down_read(&ctrl->reset_lock); + if (!pciehp_check_link_active(ctrl)) + pciehp_request(ctrl, PCI_EXP_SLTSTA_DLLSC); + up_read(&ctrl->reset_lock); +} + static irqreturn_t pciehp_isr(int irq, void *dev_id) { struct controller *ctrl = (struct controller *)dev_id; @@ -706,6 +732,16 @@ static irqreturn_t pciehp_ist(int irq, void *dev_id) PCI_EXP_SLTCTL_ATTN_IND_ON); } + /* + * Ignore Link Down/Up events caused by Downstream Port Containment + * if recovery from the error succeeded. + */ + if ((events & PCI_EXP_SLTSTA_DLLSC) && pci_dpc_recovered(pdev) && + ctrl->state == ON_STATE) { + events &= ~PCI_EXP_SLTSTA_DLLSC; + pciehp_ignore_dpc_link_change(ctrl, pdev, irq); + } + /* * Disable requests have higher priority than Presence Detect Changed * or Data Link Layer State Changed events. diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h index 4c13e2ff05eb..587cc92e182d 100644 --- a/drivers/pci/pci.h +++ b/drivers/pci/pci.h @@ -385,6 +385,8 @@ static inline bool pci_dev_is_disconnected(const struct pci_dev *dev) /* pci_dev priv_flags */ #define PCI_DEV_ADDED 0 +#define PCI_DPC_RECOVERED 1 +#define PCI_DPC_RECOVERING 2 static inline void pci_dev_assign_added(struct pci_dev *dev, bool added) { @@ -439,10 +441,12 @@ void pci_restore_dpc_state(struct pci_dev *dev); void pci_dpc_init(struct pci_dev *pdev); void dpc_process_error(struct pci_dev *pdev); pci_ers_result_t dpc_reset_link(struct pci_dev *pdev); +bool pci_dpc_recovered(struct pci_dev *pdev); #else static inline void pci_save_dpc_state(struct pci_dev *dev) {} static inline void pci_restore_dpc_state(struct pci_dev *dev) {} static inline void pci_dpc_init(struct pci_dev *pdev) {} +static inline bool pci_dpc_recovered(struct pci_dev *pdev) { return false; } #endif #ifdef CONFIG_PCIEPORTBUS diff --git a/drivers/pci/pcie/dpc.c b/drivers/pci/pcie/dpc.c index e05aba86a317..c556e7beafe3 100644 --- a/drivers/pci/pcie/dpc.c +++ b/drivers/pci/pcie/dpc.c @@ -71,6 +71,58 @@ void pci_restore_dpc_state(struct pci_dev *dev) pci_write_config_word(dev, dev->dpc_cap + PCI_EXP_DPC_CTL, *cap); } +static DECLARE_WAIT_QUEUE_HEAD(dpc_completed_waitqueue); + +#ifdef CONFIG_HOTPLUG_PCI_PCIE +static bool dpc_completed(struct pci_dev *pdev) +{ + u16 status; + + pci_read_config_word(pdev, pdev->dpc_cap + PCI_EXP_DPC_STATUS, &status); + if ((status != 0xffff) && (status & PCI_EXP_DPC_STATUS_TRIGGER)) + return false; + + if (test_bit(PCI_DPC_RECOVERING, &pdev->priv_flags)) + return false; + + return true; +} + +/** + * pci_dpc_recovered - whether DPC triggered and has recovered successfully + * @pdev: PCI device + * + * Return true if DPC was triggered for @pdev and has recovered successfully. + * Wait for recovery if it hasn't completed yet. Called from the PCIe hotplug + * driver to recognize and ignore Link Down/Up events caused by DPC. + */ +bool pci_dpc_recovered(struct pci_dev *pdev) +{ + struct pci_host_bridge *host; + + if (!pdev->dpc_cap) + return false; + + /* + * Synchronization between hotplug and DPC is not supported + * if DPC is owned by firmware and EDR is not enabled. + */ + host = pci_find_host_bridge(pdev->bus); + if (!host->native_dpc && !IS_ENABLED(CONFIG_PCIE_EDR)) + return false; + + /* + * Need a timeout in case DPC never completes due to failure of + * dpc_wait_rp_inactive(). The spec doesn't mandate a time limit, + * but reports indicate that DPC completes within 4 seconds. + */ + wait_event_timeout(dpc_completed_waitqueue, dpc_completed(pdev), + msecs_to_jiffies(4000)); + + return test_and_clear_bit(PCI_DPC_RECOVERED, &pdev->priv_flags); +} +#endif /* CONFIG_HOTPLUG_PCI_PCIE */ + static int dpc_wait_rp_inactive(struct pci_dev *pdev) { unsigned long timeout = jiffies + HZ; @@ -91,8 +143,11 @@ static int dpc_wait_rp_inactive(struct pci_dev *pdev) pci_ers_result_t dpc_reset_link(struct pci_dev *pdev) { + pci_ers_result_t ret; u16 cap; + set_bit(PCI_DPC_RECOVERING, &pdev->priv_flags); + /* * DPC disables the Link automatically in hardware, so it has * already been reset by the time we get here. @@ -106,18 +161,27 @@ pci_ers_result_t dpc_reset_link(struct pci_dev *pdev) if (!pcie_wait_for_link(pdev, false)) pci_info(pdev, "Data Link Layer Link Active not cleared in 1000 msec\n"); - if (pdev->dpc_rp_extensions && dpc_wait_rp_inactive(pdev)) - return PCI_ERS_RESULT_DISCONNECT; + if (pdev->dpc_rp_extensions && dpc_wait_rp_inactive(pdev)) { + clear_bit(PCI_DPC_RECOVERED, &pdev->priv_flags); + ret = PCI_ERS_RESULT_DISCONNECT; + goto out; + } pci_write_config_word(pdev, cap + PCI_EXP_DPC_STATUS, PCI_EXP_DPC_STATUS_TRIGGER); if (!pcie_wait_for_link(pdev, true)) { pci_info(pdev, "Data Link Layer Link Active not set in 1000 msec\n"); - return PCI_ERS_RESULT_DISCONNECT; + clear_bit(PCI_DPC_RECOVERED, &pdev->priv_flags); + ret = PCI_ERS_RESULT_DISCONNECT; + } else { + set_bit(PCI_DPC_RECOVERED, &pdev->priv_flags); + ret = PCI_ERS_RESULT_RECOVERED; } - - return PCI_ERS_RESULT_RECOVERED; +out: + clear_bit(PCI_DPC_RECOVERING, &pdev->priv_flags); + wake_up_all(&dpc_completed_waitqueue); + return ret; } static void dpc_process_rp_pio_error(struct pci_dev *pdev) -- 2.30.2
