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From: Ross Zwisler <ross.zwisler@linux.intel.com>
To: "Elliott, Robert (Persistent Memory)" <elliott@hpe.com>
Cc: Eduardo Habkost <ehabkost@redhat.com>,
	linux-nvdimm <linux-nvdimm@lists.01.org>,
	"Michael S . Tsirkin" <mst@redhat.com>,
	"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
	Stefan Hajnoczi <stefanha@redhat.com>,
	Igor Mammedov <imammedo@redhat.com>
Subject: Re: [qemu PATCH v2 3/4] nvdimm, acpi: support NFIT platform capabilities
Date: Fri, 18 May 2018 13:31:45 -0600	[thread overview]
Message-ID: <20180518193145.GA29547@linux.intel.com> (raw)
In-Reply-To: <AT5PR8401MB11694A7F7825A488105AEFADAB900@AT5PR8401MB1169.NAMPRD84.PROD.OUTLOOK.COM>

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.
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  reply	other threads:[~2018-05-18 19:31 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-17  5:00 [qemu PATCH v2 0/4] support NFIT platform capabilities Ross Zwisler
2018-05-17  5:00 ` [qemu PATCH v2 1/4] nvdimm: fix typo in label-size definition Ross Zwisler
2018-05-17  5:00 ` [qemu PATCH v2 2/4] tests/.gitignore: add entry for generated file Ross Zwisler
2018-05-17  5:00 ` [qemu PATCH v2 3/4] nvdimm, acpi: support NFIT platform capabilities Ross Zwisler
2018-05-17 22:06   ` Elliott, Robert (Persistent Memory)
2018-05-18 15:23     ` Ross Zwisler
2018-05-18 16:37       ` Elliott, Robert (Persistent Memory)
2018-05-18 19:31         ` Ross Zwisler [this message]
2018-05-21 15:54         ` Ross Zwisler
2018-05-17  5:00 ` [qemu PATCH v2 4/4] ACPI testing: test " Ross Zwisler
2018-05-17  5:08 ` [Qemu-devel] [qemu PATCH v2 0/4] support " no-reply
2018-05-17 15:32   ` [qemu PATCH v3 3/4] nvdimm, acpi: " Ross Zwisler

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