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SubjectRe: [PATCH v8 2/6] PCI/DPC: define a function to check and wait till port finish DPC handling
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On 10/7/20 4:31 AM, Ethan Zhao wrote:
> Once root port DPC capability is enabled and triggered, at the beginning
> of DPC is triggered, the DPC status bits are set by hardware and then
> sends DPC/DLLSC/PDC interrupts to OS DPC and pciehp drivers, it will
> take the port and software DPC interrupt handler 10ms to 50ms (test data
> on ICS(Ice Lake SP platform, see
> https://en.wikichip.org/wiki/intel/microarchitectures/ice_lake_(server)
> & stable 5.9-rc6) to complete the DPC containment procedure
This data is based on one particular architecture. So using this
to create a timed loop in pci_wait_port_outdpc() looks incorrect.

I still recommend looking for some locking model to fix this
issue (may be atomic state flag or lock).
> till the DPC status is cleared at the end of the DPC interrupt handler.
>
> We use this function to check if the root port is in DPC handling status
> and wait till the hardware and software completed the procedure.
>
> Signed-off-by: Ethan Zhao <haifeng.zhao@intel.com>
> Tested-by: Wen Jin <wen.jin@intel.com>
> Tested-by: Shanshan Zhang <ShanshanX.Zhang@intel.com>
> ---
> changes:
> v2:align ICS code name to public doc.
> v3: no change.
> v4: response to Christoph's (Christoph Hellwig <hch@infradead.org>)
> tip, move pci_wait_port_outdpc() to DPC driver and its declaration
> to pci.h.
> v5: fix building issue reported by lkp@intel.com with some config.
> v6: move from [1/5] to [2/5].
> v7: no change.
> v8: no change.
>
> drivers/pci/pci.h | 2 ++
> drivers/pci/pcie/dpc.c | 27 +++++++++++++++++++++++++++
> 2 files changed, 29 insertions(+)
>
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index fa12f7cbc1a0..455b32187abd 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -455,10 +455,12 @@ 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_wait_port_outdpc(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_wait_port_outdpc(struct pci_dev *pdev) { return false; }
> #endif
>
> #ifdef CONFIG_PCI_ATS
> diff --git a/drivers/pci/pcie/dpc.c b/drivers/pci/pcie/dpc.c
> index daa9a4153776..2e0e091ce923 100644
> --- a/drivers/pci/pcie/dpc.c
> +++ b/drivers/pci/pcie/dpc.c
> @@ -71,6 +71,33 @@ void pci_restore_dpc_state(struct pci_dev *dev)
> pci_write_config_word(dev, dev->dpc_cap + PCI_EXP_DPC_CTL, *cap);
> }
>
> +bool pci_wait_port_outdpc(struct pci_dev *pdev)
> +{
> + u16 cap = pdev->dpc_cap, status;
> + u16 loop = 0;
> +
> + if (!cap) {
> + pci_WARN_ONCE(pdev, !cap, "No DPC capability initiated\n");
> + return false;
> + }
> + pci_read_config_word(pdev, cap + PCI_EXP_DPC_STATUS, &status);
> + pci_dbg(pdev, "DPC status %x, cap %x\n", status, cap);
> +
> + while (status & PCI_EXP_DPC_STATUS_TRIGGER && loop < 100) {
> + msleep(10);
> + loop++;
> + pci_read_config_word(pdev, cap + PCI_EXP_DPC_STATUS, &status);
> + }
> +
> + if (!(status & PCI_EXP_DPC_STATUS_TRIGGER)) {
> + pci_dbg(pdev, "Out of DPC %x, cost %d ms\n", status, loop*10);
> + return true;
> + }
> +
> + pci_dbg(pdev, "Timeout to wait port out of DPC status\n");
> + return false;
> +}
> +
> static int dpc_wait_rp_inactive(struct pci_dev *pdev)
> {
> unsigned long timeout = jiffies + HZ;

--
Sathyanarayanan Kuppuswamy
Linux Kernel Developer

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