On Fri, May 18, 2018 at 04:37:10PM +0000, Elliott, Robert (Persistent Memory) wrote: > > > ... > > 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"
Yea, let me check on that. I'll update the wording regardless to try and make it more clear. > ... > > > 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 Yea, I agree that this is how we could do it, but I don't think this is necessary right now. We currently only have 3 bits in the Capabilities field, and right now there is never a case where there is a difference between "I don't know about this bit" and "I know about this bit, and it's value is 0". So, really for now we could essentially just say the highest_cap = 31 and be fine. Let's put off the nvdimm-highest-cap argument complexity until we actually have a use case where it adds value.
