Re: [PATCH 1/2] VMD: Document code for maintainability

[Bjorn Helgaas <helgaas@kernel.org>]

On Wed, Mar 02, 2016 at 03:31:03PM -0700, Keith Busch wrote:
> This comments 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: Keith Busch <keith.busch@intel.com>

I applied both patches to pci/host-vmd for v4.6, thanks, Keith!

> ---
>  arch/x86/pci/vmd.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/arch/x86/pci/vmd.c b/arch/x86/pci/vmd.c
> index d57e480..68faa5e 100644
> --- a/arch/x86/pci/vmd.c
> +++ b/arch/x86/pci/vmd.c
> @@ -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;
> -- 
> 2.7.2
> 
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