Re: [PATCH] PCI/VMD: Configure MPS settings before adding devices

[Bjorn Helgaas <helgaas@kernel.org>]

On Thu, Dec 13, 2018 at 09:23:42AM -0700, Jon Derrick wrote:
> In order to provide the most performance and/or compatible settings,
> ensure VMD root buses observe the pcie bus tuning settings by
> configuring those settings prior to adding the devices to the pcie tree.
> 
> This patch open-codes pci_rescan_bus() and configures the buses prior to
> adding devices and attaching drivers.
> 
> Signed-off-by: Jon Derrick <jonathan.derrick@intel.com>

Sorry, Lorenzo takes care of drivers/pci/controller/*, but I had
mistakenly delegated this to myself, so it probably wasn't on his
radar.

My dream is that someday pcie_bus_configure_settings() will somehow be
done as part of enumeration and host bridge drivers won't need to care
about it, but that's obviously fanciful, so this looks fine to me.

> ---
>  drivers/pci/controller/vmd.c | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
> index e50b0b5..818dda8 100644
> --- a/drivers/pci/controller/vmd.c
> +++ b/drivers/pci/controller/vmd.c
> @@ -585,6 +585,7 @@ static int vmd_enable_domain(struct vmd_dev *vmd, unsigned long features)
>  	LIST_HEAD(resources);
>  	resource_size_t offset[2] = {0};
>  	resource_size_t membar2_offset = 0x2000, busn_start = 0;
> +	struct pci_bus *child;
>  
>  	/*
>  	 * Shadow registers may exist in certain VMD device ids which allow
> @@ -712,7 +713,19 @@ static int vmd_enable_domain(struct vmd_dev *vmd, unsigned long features)
>  	vmd_attach_resources(vmd);
>  	vmd_setup_dma_ops(vmd);
>  	dev_set_msi_domain(&vmd->bus->dev, vmd->irq_domain);
> -	pci_rescan_bus(vmd->bus);
> +
> +	pci_scan_child_bus(vmd->bus);
> +	pci_assign_unassigned_bus_resources(vmd->bus);
> +
> +	/*
> +	 * VMD root buses are virtual and don't return true on pci_is_pcie()
> +	 * and will fail pcie_bus_configure_settings() early. It can instead be
> +	 * run on each of the real root ports.
> +	 */
> +	list_for_each_entry(child, &vmd->bus->children, node)
> +		pcie_bus_configure_settings(child);
> +
> +	pci_bus_add_devices(vmd->bus);
>  
>  	WARN(sysfs_create_link(&vmd->dev->dev.kobj, &vmd->bus->dev.kobj,
>  			       "domain"), "Can't create symlink to domain\n");
> -- 
> 1.8.3.1
>