Commit 83cc54a6 authored by Keith Busch's avatar Keith Busch Committed by Bjorn Helgaas
Browse files

x86/PCI: VMD: Document code for maintainability 



Comment the less obvious portion of the code for setting up memory windows,
and the platform dependency for initializing the h/w with appropriate
resources.

Signed-off-by: default avatarKeith Busch <keith.busch@intel.com>
Signed-off-by: default avatarBjorn Helgaas <bhelgaas@google.com>
parent 92e963f5

arch/x86/pci/vmd.c

+17 −0
Original line number Diff line number Diff line
@@ -532,6 +532,23 @@ static int vmd_enable_domain(struct vmd_dev *vmd) 
		.flags = IORESOURCE_BUS | IORESOURCE_PCI_FIXED,

	};



	/*

	 * If the window is below 4GB, clear IORESOURCE_MEM_64 so we can

	 * put 32-bit resources in the window.

	 *

	 * There's no hardware reason why a 64-bit window *couldn't*

	 * contain a 32-bit resource, but pbus_size_mem() computes the

	 * bridge window size assuming a 64-bit window will contain no

	 * 32-bit resources.  __pci_assign_resource() enforces that

	 * artificial restriction to make sure everything will fit.

	 *

	 * The only way we could use a 64-bit non-prefechable MEMBAR is

	 * if its address is <4GB so that we can convert it to a 32-bit

	 * resource.  To be visible to the host OS, all VMD endpoints must

	 * be initially configured by platform BIOS, which includes setting

	 * up these resources.  We can assume the device is configured

	 * according to the platform needs.

	 */

	res = &vmd->dev->resource[VMD_MEMBAR1];

	upper_bits = upper_32_bits(res->end);

	flags = res->flags & ~IORESOURCE_SIZEALIGN;