Messages in this thread | | | Subject | Re: [PATCH v2 1/1] PCI: pciehp: Skip DLLSC handling if DPC is triggered | From | "Kuppuswamy, Sathyanarayanan" <> | Date | Sat, 27 Mar 2021 22:49:45 -0700 |
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On 3/16/21 9:13 PM, Lukas Wunner wrote: > On Fri, Mar 12, 2021 at 07:32:08PM -0800, sathyanarayanan.kuppuswamy@linux.intel.com wrote: >> + if ((events == PCI_EXP_SLTSTA_DLLSC) && is_dpc_reset_active(pdev)) { >> + ctrl_info(ctrl, "Slot(%s): DLLSC event(DPC), skipped\n", >> + slot_name(ctrl)); >> + ret = IRQ_HANDLED; >> + goto out; >> + } > > Two problems here: > > (1) If recovery fails, the link will *remain* down, so there'll be > no Link Up event. You've filtered the Link Down event, thus the > slot will remain in ON_STATE even though the device in the slot is > no longer accessible. That's not good, the slot should be brought > down in this case. > > (2) If recovery succeeds, there's a race where pciehp may call > is_dpc_reset_active() *after* dpc_reset_link() has finished. > So both the DPC Trigger Status bit as well as pdev->dpc_reset_active > will be cleared. Thus, the Link Up event is not filtered by pciehp > and the slot is brought down and back up even though DPC recovery > was succesful, which seems undesirable. > > The only viable solution I see is to wait until DPC has completed. > Sinan (+cc) proposed something along those lines a couple years back: > > https://patchwork.ozlabs.org/project/linux-pci/patch/20180818065126.77912-1-okaya@kernel.org/ > > Included below please find my suggestion for how to fix this. > I've sort of combined yours and Sinan's approach, but I'm > using a waitqueue (Sinan used polling) and I'm using atomic bitops > on pdev->priv_flags (you're using an atomic_t instead, which needs > additionally space in struct pci_dev). Note: It's compile-tested > only, I don't have any DPC-capable hardware at my disposal. > > Would this work for you? If so, I can add a commit message to the > patch and submit it properly. Let me know what you think. Thanks!
> > -- >8 -- > Subject: [PATCH] PCI: pciehp: Ignore Link Down/Up caused by DPC > > Signed-off-by: Lukas Wunner <lukas@wunner.de> > --- > drivers/pci/hotplug/pciehp_hpc.c | 11 +++++++++ > drivers/pci/pci.h | 4 ++++ > drivers/pci/pcie/dpc.c | 51 ++++++++++++++++++++++++++++++++++++++-- > 3 files changed, 64 insertions(+), 2 deletions(-) > > diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c > index fb3840e..bcc018e 100644 > --- a/drivers/pci/hotplug/pciehp_hpc.c > +++ b/drivers/pci/hotplug/pciehp_hpc.c > @@ -707,6 +707,17 @@ static irqreturn_t pciehp_ist(int irq, void *dev_id) > } > > /* > + * Ignore Link Down/Up 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) { > + atomic_and(~PCI_EXP_SLTSTA_DLLSC, &ctrl->pending_events); Why modify pending_events here. It should be already be zero right? > + if (pciehp_check_link_active(ctrl) > 0) > + events &= ~PCI_EXP_SLTSTA_DLLSC; > + } > + > + /* > * 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 9684b46..e5ae5e8 100644 > --- a/drivers/pci/pci.h > +++ b/drivers/pci/pci.h > @@ -392,6 +392,8 @@ 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) > { > @@ -446,10 +448,12 @@ struct rcec_ea { > 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 e05aba8..7328d9c4 100644 > --- a/drivers/pci/pcie/dpc.c > +++ b/drivers/pci/pcie/dpc.c > @@ -71,6 +71,44 @@ void pci_restore_dpc_state(struct pci_dev *dev) > pci_write_config_word(dev, dev->dpc_cap + PCI_EXP_DPC_CTL, *cap); > } > > +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 & PCI_EXP_DPC_STATUS_TRIGGER) > + return false; > + > + if (test_bit(PCI_DPC_RECOVERING, &pdev->priv_flags)) > + return false; > + > + return true; > +} > + > +static DECLARE_WAIT_QUEUE_HEAD(dpc_completed_waitqueue); > + > +bool pci_dpc_recovered(struct pci_dev *pdev) > +{ > + struct pci_host_bridge *host; > + > + if (!pdev->dpc_cap) > + return false; > + > + /* > + * If DPC is owned by firmware and EDR is not supported, there is > + * no race between hotplug and DPC recovery handler. So return > + * false. > + */ > + host = pci_find_host_bridge(pdev->bus); > + if (!host->native_dpc && !IS_ENABLED(CONFIG_PCIE_EDR)) > + return false; > + > + wait_event_timeout(dpc_completed_waitqueue, dpc_completed(pdev), > + msecs_to_jiffies(5000)); > + > + return test_and_clear_bit(PCI_DPC_RECOVERED, &pdev->priv_flags); > +} > + > static int dpc_wait_rp_inactive(struct pci_dev *pdev) > { > unsigned long timeout = jiffies + HZ; > @@ -91,8 +129,12 @@ 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; > > + clear_bit(PCI_DPC_RECOVERED, &pdev->priv_flags); > + 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. > @@ -114,10 +156,15 @@ pci_ers_result_t dpc_reset_link(struct pci_dev *pdev) > > 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; > + ret = PCI_ERS_RESULT_DISCONNECT; > + } else { > + set_bit(PCI_DPC_RECOVERED, &pdev->priv_flags); > + ret = PCI_ERS_RESULT_RECOVERED; > } > > - return PCI_ERS_RESULT_RECOVERED; > + 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) >
-- Sathyanarayanan Kuppuswamy Linux Kernel Developer
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