linux-kernel - Re: [PATCH v8 2/6] PCI/DPC: define a function to check and wait till port finish DPC handling

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Date:   Wed, 7 Oct 2020 10:28:50 -0700
From:   "Kuppuswamy, Sathyanarayanan" <sathyanarayanan.kuppuswamy@...el.com>
To:     Ethan Zhao <haifeng.zhao@...el.com>, bhelgaas@...gle.com,
        oohall@...il.com, ruscur@...sell.cc, lukas@...ner.de,
        andriy.shevchenko@...ux.intel.com, stuart.w.hayes@...il.com,
        mr.nuke.me@...il.com, mika.westerberg@...ux.intel.com
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        ashok.raj@...ux.intel.com, xerces.zhao@...il.com
Subject: Re: [PATCH v8 2/6] PCI/DPC: define a function to check and wait till
 port finish DPC handling


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@...el.com>
> Tested-by: Wen Jin <wen.jin@...el.com>
> Tested-by: Shanshan Zhang <ShanshanX.Zhang@...el.com>
> ---
> changes:
>   v2：align ICS code name to public doc.
>   v3: no change.
>   v4: response to Christoph's (Christoph Hellwig <hch@...radead.org>)
>       tip, move pci_wait_port_outdpc() to DPC driver and its declaration
>       to pci.h.
>   v5: fix building issue reported by lkp@...el.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