Re: [edk2-devel] [PATCH] MdeModulePkg/PciBusDxe: Fix hotplug functionality for USB4 bridge

["Ding, Feng (Sunnyvale) via groups.io" <feng1.ding=amd.com@groups.io>]

[AMD Official Use Only - General]

Hi Laszlo,

" MdeModulePkg/PciBusDxe: plug device hierarchy leak upon bridge hot-unplug " is perfect description for the issue.
"a root bridge" is "a (PCIe Hotplug) bridge", locating anywhere.

Thanks
feng

-----Original Message-----
From: Laszlo Ersek <lersek@redhat.com>
Sent: Wednesday, February 7, 2024 12:51 PM
To: devel@edk2.groups.io; Hsueh, Hong-Chih (Neo) <Hong-Chih.Hsueh@amd.com>
Cc: Ding, Feng (Sunnyvale) <feng1.ding@amd.com>; He, Jiangang <Jiangang.He@amd.com>; Chang, Abner <Abner.Chang@amd.com>; ray.ni@intel.com; gaoliming@byosoft.com.cn
Subject: Re: [edk2-devel] [PATCH] MdeModulePkg/PciBusDxe: Fix hotplug functionality for USB4 bridge

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On 2/6/24 23:34, Hsueh, Hong-Chih (Neo) via groups.io wrote:
> A USB4 or TBT bridge can be plugged or unplugged on USB4 port. The actions require PciHotPlugRequestNotify to add a root bridge or remove a root bridge completely.
> In the plug-unplug-plug scenerio, PciHotPlugRequestNotify will return with no-action on second plug because bridge tree shows configured.
> Destroy Pci Device Tree in function PciHotPlugRequestNotify for unplug event to fix this issue.
>
> Cc: Feng Ding <feng1.ding@amd.com>
> Cc: Jiangang He <jiangang.he@amd.com>
> Signed-off-by: Neo Hsueh <Hong-Chih.Hsueh@amd.com>
> ---
>  MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumerator.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumerator.c b/MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumerator.c
> index 3f8c6e6da7..2b7af60e0a 100644
> --- a/MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumerator.c
> +++ b/MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumerator.c
> @@ -2103,6 +2103,8 @@ PciHotPlugRequestNotify (
>        }
>      }
>
> +    DestroyPciDeviceTree (Bridge);
> +
>      //
>      // End for
>      //

I think the subject line is too specific. This patch appears to fix a general resource leak in the PCI hot-unplug functionality. Writing up the USB4 angle in the commit message is welcome in my opinion, but the subject should state something like:

MdeModulePkg/PciBusDxe: plug device hierarchy leak upon bridge hot-unplug

(And I think the bridge doesn't even have to be a *root* bridge for the leak to occur; is that right?)

Laszlo



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