Re: [PATCH V3] PCI: vmd: Fix secondary bus reset for Intel bridges

["Munoz Ruiz, Francisco" <francisco.munoz.ruiz@linux.intel.com>]

On 11/3/2022 1:14 PM, francisco.munoz.ruiz@linux.intel.com wrote:
> From: Francisco Munoz <francisco.munoz.ruiz@linux.intel.com>
> 
> The reset was never applied in the current implementation because Intel
> Bridges owned by VMD are parentless. Internally, pci_reset_bus() applies
> a reset to the parent of the PCI device supplied as argument, but in this
> case it failed because there wasn't a parent.
> 
> In more detail, this change allows the VMD driver to enumerate NVMe devices
> in pass-through configurations when guest reboots are performed. Commit id
> 6aab5622296b ("PCI: vmd: Clean up domain before enumeration") attempted to
> fix this, but later we discovered that the code inside pci_reset_bus() wasn’t
> triggering secondary bus resets.  Therefore, we updated the parameters passed
> to it, and now NVMe SSDs attached to VMD bridges are properly enumerated in
> VT-d pass-through scenarios.
> 
> Signed-off-by: Francisco Munoz <francisco.munoz.ruiz@linux.intel.com>
> Reviewed-by: Nirmal Patel <nirmal.patel@linux.intel.com>
> Reviewed-by: Jonathan Derrick <jonathan.derrick@linux.dev>
> ---
> V3:
>     - Add WARN_ON
>     - Include Jonathan as reviewer
>     - Update commit message
> V2:
>     - Update commit message
> 
>  drivers/pci/controller/vmd.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
> index e06e9f4fc50f..2406be6644f3 100644
> --- a/drivers/pci/controller/vmd.c
> +++ b/drivers/pci/controller/vmd.c
> @@ -859,8 +859,17 @@ static int vmd_enable_domain(struct vmd_dev *vmd, unsigned long features)
>  
>  	pci_scan_child_bus(vmd->bus);
>  	vmd_domain_reset(vmd);
> -	list_for_each_entry(child, &vmd->bus->children, node)
> -		pci_reset_bus(child->self);
> +
> +	list_for_each_entry(child, &vmd->bus->children, node) {
> +		if (!list_empty(&child->devices)) {
> +			ret = pci_reset_bus(list_first_entry(&child->devices,
> +							     struct pci_dev,
> +							     bus_list));
> +			WARN_ON(ret);
> +			break;
> +		}
> +	}
> +
>  	pci_assign_unassigned_bus_resources(vmd->bus);
>  
>  	/*


Hi,

Just a gentle reminder for this one

Best wishes,
Francisco.