Re: [PATCH v5 3/9] PCI: pciehp: Clear Presence Detect and Data Link Layer Status Changed on resume

[Bjorn Helgaas <helgaas@kernel.org>]

Hi Mika,

On Mon, Apr 16, 2018 at 01:34:47PM +0300, Mika Westerberg wrote:
> After suspend/resume cycle the Presence Detect or Data Link Layer Status
> Changed bits might be set and if we don't clear them those events will
> not fire anymore and nothing happens for instance when a device is now
> hot-unplugged.
> 
> Fix this by clearing those bits in a newly introduced function
> pcie_reenable_notification(). This should be fine because immediately
> after we check if the adapter is still present by reading directly from
> the status register.
> 
> Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> Cc: stable@vger.kernel.org

I want to understand why we need to handle this differently between
the boot-time probe path and the resume path.

This patch clears PCI_EXP_SLTSTA_PDC and PCI_EXP_SLTSTA_DLLSC in the
resume path:

  pciehp_resume
    pcie_reenable_notification
      # clear PDC DLLSC
      pcie_enable_notification
        # set DLLSCE ABPE/PDCE HPIE CCIE
    pciehp_get_adapter_status
      # read PCI_EXP_SLTSTA

We used to clear PCI_EXP_SLTSTA_PDC and PCI_EXP_SLTSTA_DLLSC in the
probe path:

  pciehp_probe
    pcie_init
      # clear PDC ABP PFD MRLSC CC DLSCC
    pcie_init_notification
      pciehp_request_irq
      pcie_enable_notification
        # set DLLSCE ABPE/PDCE HPIE CCIE
    pciehp_get_adapter_status
      # read PCI_EXP_SLTSTA
    pciehp_get_power_status

db63d40017a5 ("PCI: pciehp: Do not clear Presence Detect Changed
during initialization") changed the probe path so we don't clear
PCI_EXP_SLTSTA_PDC there anymore.  This was so we wouldn't miss a PDC
interrupt that happened before probe.

Why can't we handle probe and resume the same way?  They look quite
similar.

You say this patch should be fine because we read SLTSTA immediately
after clearing PDC and DLLSC.  But we also read SLTSTA in the probe
path, so I'm not sure why we need to clear PDC and DLLSC for resume
but not for probe.

> ---
>  drivers/pci/hotplug/pciehp.h      |  2 +-
>  drivers/pci/hotplug/pciehp_core.c |  2 +-
>  drivers/pci/hotplug/pciehp_hpc.c  | 13 ++++++++++++-
>  3 files changed, 14 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/pci/hotplug/pciehp.h b/drivers/pci/hotplug/pciehp.h
> index 88e917c9120f..5f892065585e 100644
> --- a/drivers/pci/hotplug/pciehp.h
> +++ b/drivers/pci/hotplug/pciehp.h
> @@ -121,7 +121,7 @@ struct controller *pcie_init(struct pcie_device *dev);
>  int pcie_init_notification(struct controller *ctrl);
>  int pciehp_enable_slot(struct slot *p_slot);
>  int pciehp_disable_slot(struct slot *p_slot);
> -void pcie_enable_notification(struct controller *ctrl);
> +void pcie_reenable_notification(struct controller *ctrl);
>  int pciehp_power_on_slot(struct slot *slot);
>  void pciehp_power_off_slot(struct slot *slot);
>  void pciehp_get_power_status(struct slot *slot, u8 *status);
> diff --git a/drivers/pci/hotplug/pciehp_core.c b/drivers/pci/hotplug/pciehp_core.c
> index 332b723ff9e6..44a6a63802d5 100644
> --- a/drivers/pci/hotplug/pciehp_core.c
> +++ b/drivers/pci/hotplug/pciehp_core.c
> @@ -283,7 +283,7 @@ static int pciehp_resume(struct pcie_device *dev)
>  	ctrl = get_service_data(dev);
>  
>  	/* reinitialize the chipset's event detection logic */
> -	pcie_enable_notification(ctrl);
> +	pcie_reenable_notification(ctrl);
>  
>  	slot = ctrl->slot;
>  
> diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
> index 18a42f8f5dc5..98ea75aa32c7 100644
> --- a/drivers/pci/hotplug/pciehp_hpc.c
> +++ b/drivers/pci/hotplug/pciehp_hpc.c
> @@ -659,7 +659,7 @@ static irqreturn_t pcie_isr(int irq, void *dev_id)
>  	return handled;
>  }
>  
> -void pcie_enable_notification(struct controller *ctrl)
> +static void pcie_enable_notification(struct controller *ctrl)
>  {
>  	u16 cmd, mask;
>  
> @@ -697,6 +697,17 @@ void pcie_enable_notification(struct controller *ctrl)
>  		 pci_pcie_cap(ctrl->pcie->port) + PCI_EXP_SLTCTL, cmd);
>  }
>  
> +void pcie_reenable_notification(struct controller *ctrl)
> +{
> +	/*
> +	 * Clear both Presence and Data Link Layer Changed to make sure
> +	 * those events still fire after we have re-enabled them.
> +	 */
> +	pcie_capability_write_word(ctrl->pcie->port, PCI_EXP_SLTSTA,
> +				   PCI_EXP_SLTSTA_PDC | PCI_EXP_SLTSTA_DLLSC);
> +	pcie_enable_notification(ctrl);
> +}
> +
>  static void pcie_disable_notification(struct controller *ctrl)
>  {
>  	u16 mask;
> -- 
> 2.16.3
> 
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