Re: [Qemu-devel] [qemu PATCH v2 3/4] nvdimm, acpi: support NFIT platform capabilities

[Elliott, Robert (Persistent Memory)]

...
> Would it help to show them in hex?
> 
>   As of ACPI 6.2 Errata A, the following values are valid for the bottom
>   two bits:
> 
>   0x2 - Memory Controller Flush to NVDIMM Durability on Power Loss Capable.
>   0x3 - CPU Cache Flush to NVDIMM Durability on Power Loss Capable.

Yes, that helps (unless the parser for that command-line does not 
accept hex values).

It would also help to make the text be:
        "CPU Cache and Memory Controller Flush"

...
> > So, there should be a way to specify a highest_cap value to convey that
> > some of the upper capabilities bits are valid and contain 0.
> 
> Right, I'll make this dynamic based on the capabilities value passed in by
> the user.  That's a much better solution, thanks.  This should cover all the
> same cases as you have outlined above, without burdening the user with yet
> another input value.

Automatically determining the highest bit that the user wants to set to 1
should be easy, and will probably be the most common case.

It's harder to let the user set some upper bits to 0 but also have them
within the highest_cap range.  Since this will be less common, the syntax
could be more convoluted, like an optional highest_cap argument
to override the automatically generated value.

For example, to report bits 7, 1 and 0 are all set to 1:
        -machine pc,accel=kvm,nvdimm,nvdimm-cap=0x83
would automatically set highest_cap to 7.

To report bit 7 set to 0 while bits 1 and 0 are set to 1:
        -machine pc,accel=kvm,nvdimm,nvdimm-cap=0x3,nvdimm-highest-cap=7