linux-kernel - RE: [RFC] fdt:free the fdt reserved memory

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Date:	Fri, 5 Dec 2014 10:38:10 +0800
From:	"Wang, Yalin" <Yalin.Wang@...ymobile.com>
To:	'Grant Likely' <grant.likely@...aro.org>
CC:	"robh+dt@...nel.org" <robh+dt@...nel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"pawel.moll@....com" <pawel.moll@....com>,
	"mark.rutland@....com" <mark.rutland@....com>,
	"ijc+devicetree@...lion.org.uk" <ijc+devicetree@...lion.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [RFC] fdt:free the fdt reserved memory

> -----Original Message-----
> From: glikely@...retlab.ca [mailto:glikely@...retlab.ca] On Behalf Of Grant
> Likely
> Sent: Thursday, December 04, 2014 8:46 PM
> To: Wang, Yalin
> Cc: robh+dt@...nel.org; devicetree@...r.kernel.org; pawel.moll@....com;
> mark.rutland@....com; ijc+devicetree@...lion.org.uk; linux-
> kernel@...r.kernel.org
> Subject: Re: [RFC] fdt:free the fdt reserved memory
> 
> On Thu, Dec 4, 2014 at 10:23 AM, Wang, Yalin <Yalin.Wang@...ymobile.com>
> wrote:
> >> -----Original Message-----
> >> From: Grant Likely [mailto:glikely@...retlab.ca] On Behalf Of Grant
> >> Likely
> >> Sent: Thursday, December 04, 2014 6:05 PM
> >> To: Wang, Yalin; 'robh+dt@...nel.org'; 'devicetree@...r.kernel.org';
> >> 'pawel.moll@....com'; 'mark.rutland@....com';
> >> 'ijc+devicetree@...lion.org.uk'; 'linux-kernel@...r.kernel.org'
> >> Subject: RE: [RFC] fdt:free the fdt reserved memory
> >>
> >> On Thu, 4 Dec 2014 14:56:11 +0800
> >> , "Wang, Yalin" <Yalin.Wang@...ymobile.com>
> >>  wrote:
> >> > > -----Original Message-----
> >> > > From: Grant Likely [mailto:glikely@...retlab.ca] On Behalf Of
> >> > > Grant Likely
> >> > > Sent: Wednesday, September 24, 2014 10:45 PM
> >> > > To: Wang, Yalin; 'robh+dt@...nel.org';
> >> > > 'devicetree@...r.kernel.org'; 'pawel.moll@....com';
> >> > > 'mark.rutland@....com'; 'ijc+devicetree@...lion.org.uk'; 'linux-
> kernel@...r.kernel.org'
> >> > > Subject: Re: [RFC] fdt:free the fdt reserved memory
> >> > >
> >> > > On Thu, 18 Sep 2014 17:25:12 +0800, "Wang, Yalin"
> >> > > <Yalin.Wang@...ymobile.com> wrote:
> >> > > > This patch make some change to unflatten_dt_node(), make sure
> >> > > > the device_node don't reference to fdt raw blob memory, so that
> >> > > > we can free the raw blob reserved memory after initcalls.
> >> > > >
> >> > > > Signed-off-by: Yalin Wang <yalin.wang@...ymobile.com>
> >> > >
> >> > > Do you have any measurements showing a change in available memory
> >> > > before and after the patch?
> >> > >
> >> > Does anyone have a look at this patch?
> >> > It can save 12K on my platform,
> >> > My dtb is 164K
> >>
> >> Yes, I've been thinking about this one. Unfortunately there is a
> >> conflict with another feature that I'm merging for v3.19. See commit
> >> 08d53aa5,
> >> "of/fdt: export fdt blob as /sys/firmware/fdt" in linux-next.
> >> That commit requires the original blob to be kept around.
> >>
> >> In order to free the original dtb, the /sys/firmware/fdt feature will
> >> need to be changed to let it be configured out. All things
> >> considered, that is probably the right thing to do, but doing so
> >> increases the memory load for the platforms that want
> >> /sys/firmware/fdt. I'd like to see what the impact would be on the
> >> code to switch to this method when /sys/firmware/fdt is configured out.
> >>
> > Oh, I understand,
> > If enable /sys/firmware/fdt feature patch, doesn't need My patch is
> > fine, So need 2 method to unflatten dtb blob.
> 
> I don't want to duplicate the function. It would instead need to be a build
> time configuration to the function that if /sys/firmware/fdt is enabled,
> then copying the property on unflatten is disabled.
Yeah, seems a better way if you do like this.

BRs
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