linux-kernel - Re: [PATCH v3 2/4] PCI/portdrv: Add necessary wait for disabling hotplug events

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Message-ID: <abb50795-df83-511a-8850-cdf30f187935@linux.intel.com>
Date: Mon, 24 Feb 2025 17:00:03 +0200 (EET)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: Feng Tang <feng.tang@...ux.alibaba.com>
cc: Bjorn Helgaas <bhelgaas@...gle.com>, Lukas Wunner <lukas@...ner.de>, 
    Sathyanarayanan Kuppuswamy <sathyanarayanan.kuppuswamy@...ux.intel.com>, 
    Liguang Zhang <zhangliguang@...ux.alibaba.com>, 
    Guanghui Feng <guanghuifeng@...ux.alibaba.com>, 
    "Rafael J. Wysocki" <rafael@...nel.org>, 
    Markus Elfring <Markus.Elfring@....de>, lkp@...el.com, 
    Jonathan Cameron <Jonathan.Cameron@...wei.com>, linux-pci@...r.kernel.org, 
    LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 2/4] PCI/portdrv: Add necessary wait for disabling
 hotplug events

On Mon, 24 Feb 2025, Feng Tang wrote:

> There was problem reported by firmware developers that they received
> two PCIe hotplug commands in very short intervals on an ARM server,
> which doesn't comply with PCIe spec, and broke their state machine and
> work flow. According to PCIe 6.1 spec, section 6.7.3.2, software needs
> to wait at least 1 second for the command-complete event, before
> resending the command or sending a new command.
> 
> In the failure case, the first PCIe hotplug command firmware received
> is from get_port_device_capability(), which sends command to disable
> PCIe hotplug interrupts without waiting for its completion, and the
> second command comes from pcie_enable_notification() of pciehp driver,
> which enables hotplug interrupts again.
> 
> Fix it by adding the necessary wait to comply with PCIe spec.
> 
> Fixes: 2bd50dd800b5 ("PCI: PCIe: Disable PCIe port services during port initialization")
> Originally-by: Liguang Zhang <zhangliguang@...ux.alibaba.com>
> Signed-off-by: Feng Tang <feng.tang@...ux.alibaba.com>
> ---
>  drivers/pci/pci.h          |  2 ++
>  drivers/pci/pcie/portdrv.c | 19 +++++++++++++++++--
>  2 files changed, 19 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index 4c94a589de4a..a1138ebc2689 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -760,6 +760,7 @@ static inline void pcie_ecrc_get_policy(char *str) { }
>  void pcie_reset_lbms_count(struct pci_dev *port);
>  int pcie_lbms_count(struct pci_dev *port, unsigned long *val);
>  int pcie_poll_sltctl_cmd(struct pci_dev *dev, int timeout_ms);
> +void pcie_disable_hp_interrupts_early(struct pci_dev *dev);
>  #else
>  static inline void pcie_reset_lbms_count(struct pci_dev *port) {}
>  static inline int pcie_lbms_count(struct pci_dev *port, unsigned long *val)
> @@ -770,6 +771,7 @@ static inline int pcie_poll_sltctl_cmd(struct pci_dev *dev, int timeout_ms)
>  {
>  	return 0;
>  }
> +static inline void pcie_disable_hp_interrupts_early(struct pci_dev *dev) {}
>  #endif
>  
>  struct pci_dev_reset_methods {
> diff --git a/drivers/pci/pcie/portdrv.c b/drivers/pci/pcie/portdrv.c
> index bb00ba45ee51..ca4f21dff486 100644
> --- a/drivers/pci/pcie/portdrv.c
> +++ b/drivers/pci/pcie/portdrv.c
> @@ -230,6 +230,22 @@ int pcie_poll_sltctl_cmd(struct pci_dev *dev, int timeout_ms)
>  	return  ret;
>  }
>  
> +void pcie_disable_hp_interrupts_early(struct pci_dev *dev)
> +{
> +	u16 slot_ctrl = 0;

Unnecessary initialization

> +
> +	pcie_capability_read_word(dev, PCI_EXP_SLTCTL, &slot_ctrl);
> +	/* Bail out early if it is already disabled */
> +	if (!(slot_ctrl & (PCI_EXP_SLTCTL_CCIE | PCI_EXP_SLTCTL_HPIE)))
> +		return;
> +
> +	pcie_capability_clear_word(dev, PCI_EXP_SLTCTL,
> +		  PCI_EXP_SLTCTL_CCIE | PCI_EXP_SLTCTL_HPIE);

Align to (. You might need to put the bits to own lines.

> +
> +	if (pcie_poll_sltctl_cmd(dev, 1000))
> +		pci_info(dev, "Timeout on disabling PCIe hot-plug interrupt\n");
> +}
> +
>  /**
>   * get_port_device_capability - discover capabilities of a PCI Express port
>   * @dev: PCI Express port to examine
> @@ -255,8 +271,7 @@ static int get_port_device_capability(struct pci_dev *dev)
>  		 * Disable hot-plug interrupts in case they have been enabled
>  		 * by the BIOS and the hot-plug service driver is not loaded.
>  		 */
> -		pcie_capability_clear_word(dev, PCI_EXP_SLTCTL,
> -			  PCI_EXP_SLTCTL_CCIE | PCI_EXP_SLTCTL_HPIE);
> +		pcie_disable_hp_interrupts_early(dev);

Doesn't calling this here delay setup for all portdrv services, not just 
hotplug? And the delay can be relatively long.

>  	}
>  
>  #ifdef CONFIG_PCIEAER
> 

-- 
 i.