linux-kernel - Re: [PATCH v2 1/3] ACPI/NFIT: Update Control Region Structure to comply ACPI 6.1

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Date:	Tue, 01 Mar 2016 10:36:59 -0700
From:	Toshi Kani <toshi.kani@....com>
To:	"Moore, Robert" <robert.moore@...el.com>,
	"rjw@...ysocki.net" <rjw@...ysocki.net>,
	"Williams, Dan J" <dan.j.williams@...el.com>
Cc:	"Zheng, Lv" <lv.zheng@...el.com>,
	"elliott@....com" <elliott@....com>,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...ica.org" <devel@...ica.org>
Subject: Re: [PATCH v2 1/3] ACPI/NFIT: Update Control Region Structure to
 comply ACPI 6.1

On Tue, 2016-03-01 at 16:03 +0000, Moore, Robert wrote:
> We have a bunch of macros in include/acmacros.h -- like this:
> 
> ACPI_MOVE_16_TO_16(d, s)

There is a problem in using the ACPICA byte-swap macros.  ACPI is little-
endian arch, so the macros are set to perform byte-swappings when the CPU
arch is big-endian.  This case, however, is the other way around.  The
fields in question are defined & stored as arrays of bytes.  If you treat
them as multi-bytes numeric values, then you need to byte-swap them when
the CPU arch is little-endian because arrays of bytes have the same
addressing as big-endian.

Another issue is that it is not clear who needs to perform the byte-
swapping among ACPICA and drivers.  If ACPICA, drivers must agree that
these fields are always treated as multi-bytes numeric values despite of
the spec.  If drivers, we need to make sure that only a single driver
performs this byte-swapping one time as ACPI tables are global structures.

I think it is much clearer to define the structure according to the ACPI
spec.

Thanks,
-Toshi

> > -----Original Message-----
> > From: Toshi Kani [mailto:toshi.kani@....com]
> > Sent: Tuesday, March 01, 2016 8:38 AM
> > To: Moore, Robert; rjw@...ysocki.net; Williams, Dan J
> > Cc: Zheng, Lv; elliott@....com; linux-nvdimm@...ts.01.org; linux-
> > acpi@...r.kernel.org; linux-kernel@...r.kernel.org; devel@...ica.org
> > Subject: Re: [PATCH v2 1/3] ACPI/NFIT: Update Control Region Structure
> > to
> > comply ACPI 6.1
> > 
> > On Tue, 2016-03-01 at 15:13 +0000, Moore, Robert wrote:
> > > 
> > > > -----Original Message-----
> > > > From: Toshi Kani [mailto:toshi.kani@....com]
> > > > Sent: Monday, February 22, 2016 1:55 PM
> > > > To: rjw@...ysocki.net; Williams, Dan J
> > > > Cc: Moore, Robert; Zheng, Lv; elliott@....com;
> > > > linux-nvdimm@...ts.01.or g; linux-acpi@...r.kernel.org;
> > > > linux-kernel@...r.kernel.org; devel@...ica.org; Toshi Kani
> > > > Subject: [PATCH v2 1/3] ACPI/NFIT: Update Control Region Structure
> > > > to comply ACPI 6.1
> > > > 
> > > > ACPI 6.1, Table 5-133, updates NVDIMM Control Region Structure as
> > > > follows.
> > > >  - Valid Fields, Manufacturing Location, and Manufacturing Date
> > > >    are added from reserved range.  No change in the structure size.
> > > >  - IDs defined as SPD values are arrays of bytes.  The spec
> > > >    clarified that they need to be represented as arrays of bytes
> > > >    as well.
> > > > 
> > > > This patch makes the following changes to support this update.
> > > >  - Change 'struct acpi_nfit_control_region' to reflect the update.
> > > >    SPD IDs are defined as arrays of bytes, so that they can be
> > > >    treated in the same way regardless of CPU endianness and are
> > > >    not miss-treated as little-endian numeric values.
> > > 
> > > 
> > > I don't think we are going to start changing the ACPI tables defined
> > > in the ACPICA headers because of this. We do in fact have macros for
> > > this purpose.
> > 
> > Can you elaborate what macros you suggest to use for this purpose?
> > 
> > Thanks,
> > -Toshi
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