linux-kernel - RE: [PATCH 3/3] ACPI: Evaluate _CRS while creating device node objects

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Message-ID: <94F2FBAB4432B54E8AACC7DFDE6C92E346BD8CD0@ORSMSX101.amr.corp.intel.com>
Date:	Wed, 14 Nov 2012 14:20:00 +0000
From:	"Moore, Robert" <robert.moore@...el.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
CC:	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	"mathias.nyman@...ux.intel.com" <mathias.nyman@...ux.intel.com>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"lenb@...nel.org" <lenb@...nel.org>,
	"Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
	"broonie@...nsource.wolfsonmicro.com" 
	<broonie@...nsource.wolfsonmicro.com>,
	"grant.likely@...retlab.ca" <grant.likely@...retlab.ca>,
	"linus.walleij@...aro.org" <linus.walleij@...aro.org>,
	"khali@...ux-fr.org" <khali@...ux-fr.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"Zheng, Lv" <lv.zheng@...el.com>
Subject: RE: [PATCH 3/3] ACPI: Evaluate _CRS while creating device node
 objects

> And I can define acpi_free_buffer() in the Linux-specific code too.
> 
> Thanks,
> Rafael

I'll be glad to add an ACPI_FREE_BUFFER macro, although we've had complaints over the years that ACPICA uses too many macros. (Not so many complaints in the last 5 years, however.)

Bob


> -----Original Message-----
> From: Rafael J. Wysocki [mailto:rjw@...k.pl]
> Sent: Wednesday, November 14, 2012 1:33 AM
> To: Moore, Robert
> Cc: Mika Westerberg; mathias.nyman@...ux.intel.com; linux-
> acpi@...r.kernel.org; linux-kernel@...r.kernel.org; lenb@...nel.org;
> Wysocki, Rafael J; broonie@...nsource.wolfsonmicro.com;
> grant.likely@...retlab.ca; linus.walleij@...aro.org; khali@...ux-fr.org;
> Bjorn Helgaas; Zheng, Lv
> Subject: Re: [PATCH 3/3] ACPI: Evaluate _CRS while creating device node
> objects
> 
> On Wednesday, November 14, 2012 10:18:46 AM Rafael J. Wysocki wrote:
> > On Wednesday, November 14, 2012 02:23:51 AM Moore, Robert wrote:
> > > Rafael,
> > >
> > > I sounds like with a few changes, we can enhance this mechanism to
> > > be more useful to you and others. Some comments below. I need to
> > > look at the code in question a bit more, but I see no insurmountable
> issues.
> >
> > Great, thanks!
> >
> >
> > > > -----Original Message-----
> > > > From: Rafael J. Wysocki [mailto:rjw@...k.pl]
> > > > Sent: Tuesday, November 13, 2012 2:57 PM
> > > > To: Moore, Robert
> > > > Cc: Mika Westerberg; mathias.nyman@...ux.intel.com; linux-
> > > > acpi@...r.kernel.org; linux-kernel@...r.kernel.org;
> > > > lenb@...nel.org; Wysocki, Rafael J;
> > > > broonie@...nsource.wolfsonmicro.com;
> > > > grant.likely@...retlab.ca; linus.walleij@...aro.org;
> > > > khali@...ux-fr.org; Bjorn Helgaas; Zheng, Lv
> > > > Subject: Re: [PATCH 3/3] ACPI: Evaluate _CRS while creating device
> > > > node objects
> > > >
> > > > On Tuesday, November 13, 2012 10:06:03 PM Moore, Robert wrote:
> > > > > I may not quite understand what you are asking for, but I will
> try.
> > > > > It seems like we already have much of what you want/need, so
> > > > > maybe I'm missing something.
> > > >
> > > > I think all of the necessary pieces are there.
> > > >
> > > > > > So what I would like to have, in general terms, is something
> > > > > > like
> > > > > > acpi_walk_resources() split into three parts:
> > > > > >
> > > > > >  (1) One that processes the _CRS output and creates a list of
> > > > > >      struct acpi_resource objects for us to play with.  I
> suppose
> > > > > >      it's OK if that's just a buffer filled with resource
> objects,
> > > > > >      but a linked list might be more convenient.
> > > > > >
> > > > >
> > > > > This sounds like AcpiGetCurrentResources. It executes _CRS and
> > > > > formats the data into acpi_resource objects.
> > > >
> > > > Yes, it does.  However, it is not completely clear to me if/how
> > > > the caller is supposed to prepare the buffer object pointed to by
> the second arg.
> > > >
> > > > If the buffer is initialized by AcpiGetCurrentResources, then
> > > > that's what I need for (1).
> > >
> > >
> > > It looks to me that at least AcpiGetCurrentResources does not
> > > actually ever allocate a buffer for the resource template, it
> > > expects the caller to eventually provide one of at least the size of
> the returned resource template.
> > >
> > > This is really quite a bit out-of-date as far as the memory allocation
> model.
> > > It should also support the option to just allocate the buffer of the
> > > appropriate size before returning it to the caller.
> >
> > Yes, that would be really useful.
> >
> > Ideally, I'd like to be able to pass a pointer to an uninitialized
> > buffer structure to it (or to a wrapper around it) and get a buffer
> > full of struct acpi_resource objects (if _CRS returns any) back from
> > it. :-)
> 
> Of course, I can add such a wrapper in the Linux-specific code just fine.
> 
> 
> > > > > >  (2) One that allows us to access (read/write) resources in the
> > > > > >      list returned by (1).  We don't need to open code walking
> > > > > >      the list and I probably wouldn't event want to do that.
> What
> > > > > >      we need is to be able to walk the same list for a number of
> > > > > >      times and possibly to modify values in the resource objects
> > > > > >      if there are conflicts.
> > > > >
> > > > > This sounds like AcpiWalkResources. I suppose a possible issue
> > > > > is that currently, AcpiWalkResources actually invokes the _CRS,
> > > > > _PRS, or _AEI method on behalf of the caller.
> > > >
> > > > Yes, that exactly is the problem.
> > > >
> > > > > It might make more sense to allow the caller to pass in the
> > > > > resource buffer returned from a call to _CRS, etc.
> > > >
> > > > Yes! :-)
> > >
> > >
> > > I'll take a closer look at this tomorrow.
> >
> > Cool, thanks!
> >
> >
> > > > > >  (3) One allowing us to free the list returned by (1) if not
> needed
> > > > > >      any more.
> > > > > >
> > > > >
> > > > > AcpiGetCurrentResources: Currently, everything is returned in a
> > > > > single buffer to minimize the number of allocations. A buffer
> > > > > you can free when you are done with it.
> > > >
> > > > I suppose I should use ACPI_FREE(buffer.pointer) for that, but
> > > > isn't it for the ACPICA's internal use only?
> > > >
> > > > Besides, I would prefer to be able to pass just "buffer" for
> > > > freeing, without having to touch its internals.  No big deal, but
> > > > it would be nicer. :-)
> > >
> > >
> > > The ACPI_BUFFER type is in fact a public type that is meant to
> > > return both the buffer and the (actual) length. You will find many
> > > instances of
> > > ACPI_FREE(buffer.pointer) within existing linux code, since it also
> > > used for objects returned by control method execution/object
> evaluation.
> >
> > Well, I suppose I only wanted to say that acpi_free_buffer(buffer)
> > would look a bit more straightforward than ACPI_FREE(buffer.pointer).
> > :-)
> 
> And I can define acpi_free_buffer() in the Linux-specific code too.
> 
> Thanks,
> Rafael
> 
> 
> --
> I speak only for myself.
> Rafael J. Wysocki, Intel Open Source Technology Center.