linux-kernel - Re: [PATCH v13 1/3] PCI: make pci_dev_is_disconnected() helper public for other drivers

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Date: Thu, 22 Feb 2024 20:54:54 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Ethan Zhao <haifeng.zhao@...ux.intel.com>, bhelgaas@...gle.com,
 robin.murphy@....com, jgg@...pe.ca
Cc: baolu.lu@...ux.intel.com, kevin.tian@...el.com, dwmw2@...radead.org,
 will@...nel.org, lukas@...ner.de, yi.l.liu@...el.com,
 dan.carpenter@...aro.org, iommu@...ts.linux.dev,
 linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
 Haorong Ye <yehaorong@...edance.com>
Subject: Re: [PATCH v13 1/3] PCI: make pci_dev_is_disconnected() helper public
 for other drivers

On 2024/2/22 17:02, Ethan Zhao wrote:
> Make pci_dev_is_disconnected() public so that it can be called from
> Intel VT-d driver to quickly fix/workaround the surprise removal
> unplug hang issue for those ATS capable devices on PCIe switch downstream
> hotplug capable ports.
> 
> Beside pci_device_is_present() function, this one has no config space
> space access, so is light enough to optimize the normal pure surprise
> removal and safe removal flow.
> 
> Tested-by: Haorong Ye<yehaorong@...edance.com>
> Signed-off-by: Ethan Zhao<haifeng.zhao@...ux.intel.com>
> ---
>   drivers/pci/pci.h   | 5 -----
>   include/linux/pci.h | 5 +++++
>   2 files changed, 5 insertions(+), 5 deletions(-)

Hi PCI subsystem maintainers,

The iommu drivers (including, but not limited to, the Intel VT-d driver)
require a helper to check the physical presence of a PCI device in two
scenarios:

- During the iommu_release_device() path: This ensures the device is
   physically present before sending device TLB invalidation to device.

- During the device driver lifecycle when a device TLB invalidation
   timeout event is generated by the IOMMU hardware: This helps handle
   situations where the device might have been hot-removed.

While there may be some adjustments needed in patch 3/3, I'd like to
confirm with you whether it's feasible to expose this helper for general
use within the iommu subsystem.

If you agree with this change, I can route this patch to Linus through
the iommu tree with an "acked-by" or "reviewed-by" tag from you.

Best regards,
baolu