[PATCH v2 2/3] arm/dt: tegra: add dts file for paz00

[PATCH v2 2/3] arm/dt: tegra: add dts file for paz00

[Stephen Warren]

Marc Dietrich wrote at Friday, October 28, 2011 4:30 AM:
> Am Donnerstag, 27. Oktober 2011, 09:50:03 schrieb Stephen Warren:
> > Marc Dietrich wrote at Wednesday, October 26, 2011 1:59 PM:
> > > This adds a dts file for paz00. As a side effect, this also enables
> > > the embedded controller which controls the keyboard, touchpad, power,
> > > leds, and some other functions.
> > ...
> > > +++ b/arch/arm/boot/dts/tegra-paz00.dts
> > > @@ -0,0 +1,70 @@
> > > +/dts-v1/;
> > > +
> > > +/memreserve/ 0x1c000000 0x04000000;
> > > +/include/ "tegra20.dtsi"
> > > +
> > > +/ {
> > > +	model = "Toshiba AC100 / Dynabook AZ";
> > > +	compatible = "compal,paz00", "nvidia,tegra20";
> > > +
> > > +	chosen {
> > > +		bootargs = "mem=448 at 0 console=ttyS0,115200n8 root=/dev/mmcblk1p1";
> >
> > You shouldn't need the mem= parameter here; it wasn't in your first patch set.
> 
> that's because I forgot it. Sorry, I didn't mentioned it in the changelog. I wonder
> why mem= is still needed.

I wonder if this is some conflict between ATAGs and the DT-specified
memory node.

As far as I can tell, the kernel's memory information typically comes
from ATAGs. Some boards override what's in the ATAGs in their machine
descriptor's fixup routine, e.g. see tegra_paz00_fixup(). Presumably,
this is because of buggy bootloaders sending incorrect memory information
in the ATAGs. Do you have any way to check the ATAGs that the bootloader
is sending? Probably, you could enable DEBUG_LL and using the low-level
debugging functions to dump some of that information to the UART early
during boot.

When boards boot from DT, there is no fixup function to override the
bootloader's ATAGs. I also see a bunch of code to set up the memory
information from DT e.g. setup_machine_fdt()'s call to:

	of_scan_flat_dt(early_init_dt_scan_memory, NULL);

... but I assume that happens before the ATAGs are processed, and the
buggy ATAGs end up overriding the information in the DT file. And further,
I assume that specifying "mem=" on the command-line overrides that, thus
solving the problem.

It'd be awesome if you could validate this; the simplest way is probably
to:

a) Remove mem= from the command-line
b) Modify arch/arm/kernel/setup.c:parse_tag_mem32() to do nothing;
   comment out the call to arm_add_memory()
c) Test booting, and check what RAM size the kernel thinks you have.

If that works, then ATAGs are the problem. We probably need to modify the
core ARM code not to use memory ATAGs when there is a DT?

I'm mainly pushing on this because adding "mem=" to the command-line in
the DT file isn't a great solution; when people start using bootloaders
that rewrite the DT to include the user-specified command-line, then every
user is going to have to start specifying "mem=" in their command-lines.

> I've seen patches on the chromeos tree which try to reserve the gpu
> memory on demand. While we are at it, what is the vmalloc=192M used
> by most other boards for?

I'm not sure what vmalloc= does exactly. I somewhat doubt it's necessary
until we have code that uses the GPU in mainline. The same goes for the
/memreserve/ DT entries. I've been thinking of submitting a patch to
remove this cruft, but haven't gotten around to it yet.

-- 
nvpublic

[PATCH v2 2/3] arm/dt: tegra: add dts file for paz00

[Russell King - ARM Linux]

On Fri, Oct 28, 2011 at 09:49:49AM -0700, Stephen Warren wrote:
> When boards boot from DT, there is no fixup function to override the
> bootloader's ATAGs. I also see a bunch of code to set up the memory
> information from DT e.g. setup_machine_fdt()'s call to:
> 
> 	of_scan_flat_dt(early_init_dt_scan_memory, NULL);
> 
> ... but I assume that happens before the ATAGs are processed, and the
> buggy ATAGs end up overriding the information in the DT file.

As far as the uncompressed kernel is concerned, there is either ATAG
or DT information, never both.  If the boot loader provides ATAGs and
the zImage has a DT appended to it, the zImage decompressor merges the
ATAGs into the appended DT and passes the DT to the kernel.

So anyone who currently 'fixes' their broken boot loader via the fixup
function by directly manipulating the ATAGS is going to hit the DT
image instead.

> > I've seen patches on the chromeos tree which try to reserve the gpu
> > memory on demand. While we are at it, what is the vmalloc=192M used
> > by most other boards for?
> 
> I'm not sure what vmalloc= does exactly. I somewhat doubt it's necessary
> until we have code that uses the GPU in mainline.

It defines the size of the vmalloc and ioremap area - and limits the
maximum amount of low memory (non-highmem) available to the kernel to
achieve the specified size of the vmalloc area.  Any additional memory
will be discarded, or in the presence of a highmem enabled kernel, will
be turned into highmem.

[PATCH v2 2/3] arm/dt: tegra: add dts file for paz00

[Grant Likely]

On Sat, Oct 29, 2011 at 09:43:30AM +0100, Russell King - ARM Linux wrote:
> On Fri, Oct 28, 2011 at 09:49:49AM -0700, Stephen Warren wrote:
> > When boards boot from DT, there is no fixup function to override the
> > bootloader's ATAGs. I also see a bunch of code to set up the memory
> > information from DT e.g. setup_machine_fdt()'s call to:
> > 
> > 	of_scan_flat_dt(early_init_dt_scan_memory, NULL);
> > 
> > ... but I assume that happens before the ATAGs are processed, and the
> > buggy ATAGs end up overriding the information in the DT file.
> 
> As far as the uncompressed kernel is concerned, there is either ATAG
> or DT information, never both.  If the boot loader provides ATAGs and
> the zImage has a DT appended to it, the zImage decompressor merges the
> ATAGs into the appended DT and passes the DT to the kernel.
> 
> So anyone who currently 'fixes' their broken boot loader via the fixup
> function by directly manipulating the ATAGS is going to hit the DT
> image instead.

Ugh.  Not pretty.  A platform could still have board specific fixup
code that matches on the compatible string that deals with broken
firmware ATAGs, but I don't think that is what we want to do.

We could handle it by filling the .dts file with an empty 'reg'
property for memory, and only push in the legacy ATAG data if reg is
indeed empty.  That gives the option of overriding ATAGs if the DT
already specifies memory.  Need to think about this more.

g.

[PATCH v2 2/3] arm/dt: tegra: add dts file for paz00

[Russell King - ARM Linux]

On Sat, Oct 29, 2011 at 01:03:20PM +0200, Grant Likely wrote:
> On Sat, Oct 29, 2011 at 09:43:30AM +0100, Russell King - ARM Linux wrote:
> > On Fri, Oct 28, 2011 at 09:49:49AM -0700, Stephen Warren wrote:
> > > When boards boot from DT, there is no fixup function to override the
> > > bootloader's ATAGs. I also see a bunch of code to set up the memory
> > > information from DT e.g. setup_machine_fdt()'s call to:
> > > 
> > > 	of_scan_flat_dt(early_init_dt_scan_memory, NULL);
> > > 
> > > ... but I assume that happens before the ATAGs are processed, and the
> > > buggy ATAGs end up overriding the information in the DT file.
> > 
> > As far as the uncompressed kernel is concerned, there is either ATAG
> > or DT information, never both.  If the boot loader provides ATAGs and
> > the zImage has a DT appended to it, the zImage decompressor merges the
> > ATAGs into the appended DT and passes the DT to the kernel.
> > 
> > So anyone who currently 'fixes' their broken boot loader via the fixup
> > function by directly manipulating the ATAGS is going to hit the DT
> > image instead.
> 
> Ugh.  Not pretty.  A platform could still have board specific fixup
> code that matches on the compatible string that deals with broken
> firmware ATAGs, but I don't think that is what we want to do.

No.  The point I was making is that by the time you get to the fixup
function with a DT or even into the uncompressed kernel, even if the
boot loader provided ATAGs, your ATAGs have long since been obliterated
and are no longer available.

[PATCH v2 2/3] arm/dt: tegra: add dts file for paz00

[Stephen Warren]

Russell King wrote at Saturday, October 29, 2011 2:44 AM:
> On Fri, Oct 28, 2011 at 09:49:49AM -0700, Stephen Warren wrote:
> > When boards boot from DT, there is no fixup function to override the
> > bootloader's ATAGs. I also see a bunch of code to set up the memory
> > information from DT e.g. setup_machine_fdt()'s call to:
> >
> > 	of_scan_flat_dt(early_init_dt_scan_memory, NULL);
> >
> > ... but I assume that happens before the ATAGs are processed, and the
> > buggy ATAGs end up overriding the information in the DT file.
> 
> As far as the uncompressed kernel is concerned, there is either ATAG
> or DT information, never both.  If the boot loader provides ATAGs and
> the zImage has a DT appended to it, the zImage decompressor merges the
> ATAGs into the appended DT and passes the DT to the kernel.
> 
> So anyone who currently 'fixes' their broken boot loader via the fixup
> function by directly manipulating the ATAGS is going to hit the DT
> image instead.

I believe the PAZ00 fixup function runs on the kernel's internal data-
structures, not the ATAGs directly, so the issue you point out isn't
a problem here:

static void __init tegra_paz00_fixup(struct tag *tags, char **cmdline,
        struct meminfo *mi)
{
        mi->nr_banks = 1;
        mi->bank[0].start = PHYS_OFFSET;
        mi->bank[0].size = 448 * SZ_1M;
}

-- 
nvpublic

[PATCH v2 2/3] arm/dt: tegra: add dts file for paz00

[Marc Dietrich]

On Friday 28 October 2011 09:49:49 Stephen Warren wrote:
> Marc Dietrich wrote at Friday, October 28, 2011 4:30 AM:
> > Am Donnerstag, 27. Oktober 2011, 09:50:03 schrieb Stephen Warren:
> > > Marc Dietrich wrote at Wednesday, October 26, 2011 1:59 PM:
> > > > This adds a dts file for paz00. As a side effect, this also
> > > > enables
> > > > the embedded controller which controls the keyboard, touchpad,
> > > > power,
> > > > leds, and some other functions.
> > > 
> > > ...
> > > 
> > > > +++ b/arch/arm/boot/dts/tegra-paz00.dts
> > > > @@ -0,0 +1,70 @@
> > > > +/dts-v1/;
> > > > +
> > > > +/memreserve/ 0x1c000000 0x04000000;
> > > > +/include/ "tegra20.dtsi"
> > > > +
> > > > +/ {
> > > > +	model = "Toshiba AC100 / Dynabook AZ";
> > > > +	compatible = "compal,paz00", "nvidia,tegra20";
> > > > +
> > > > +	chosen {
> > > > +		bootargs = "mem=448 at 0 console=ttyS0,115200n8
> > > > root=/dev/mmcblk1p1";
> > > 
> > > You shouldn't need the mem= parameter here; it wasn't in your first
> > > patch set.> 
> > that's because I forgot it. Sorry, I didn't mentioned it in the
> > changelog. I wonder why mem= is still needed.
> 
> I wonder if this is some conflict between ATAGs and the DT-specified
> memory node.
> 
> As far as I can tell, the kernel's memory information typically comes
> from ATAGs. Some boards override what's in the ATAGs in their machine
> descriptor's fixup routine, e.g. see tegra_paz00_fixup(). Presumably,
> this is because of buggy bootloaders sending incorrect memory information
> in the ATAGs. Do you have any way to check the ATAGs that the bootloader
> is sending? Probably, you could enable DEBUG_LL and using the low-level
> debugging functions to dump some of that information to the UART early
> during boot.

I got the ATAGS from /proc/atags and there is no memory entry there, only 
initrd and cmdline (which is the one from nvflash).

The machine also has a fixup routine, but it also boots without (I'm sure it 
was necessary in the past),

> When boards boot from DT, there is no fixup function to override the
> bootloader's ATAGs. 

... so I guess this is why it also works with DT.

> I also see a bunch of code to set up the memory
> information from DT e.g. setup_machine_fdt()'s call to:
> 
> 	of_scan_flat_dt(early_init_dt_scan_memory, NULL);
> 
> ... but I assume that happens before the ATAGs are processed, and the
> buggy ATAGs end up overriding the information in the DT file. And further,
> I assume that specifying "mem=" on the command-line overrides that, thus
> solving the problem.
> 
> It'd be awesome if you could validate this; the simplest way is probably
> to:
> 
> a) Remove mem= from the command-line

I tested several variations. Without DT, the fixup can compensate a missing 
mem entry in the kernel command line, but with a mem= from the kernel command 
line, a fixup is not needed.

With DT, the command line specified from nvflash is ignored and the one from 
DT comes into the game. If it is also missing there, system detects 512 MB 
(which is physical right, but we cannot reserve memory for the gpu). The fixup 
is indeed ignored in this case.

> b) Modify arch/arm/kernel/setup.c:parse_tag_mem32() to do nothing;
>    comment out the call to arm_add_memory()

I leave this out because the bootloader does not send memory info in the 
ATAGS.

> c) Test booting, and check what RAM size the kernel thinks you have.

see above. RAM detection works, but it's not what we want ...

> If that works, then ATAGs are the problem. We probably need to modify the
> core ARM code not to use memory ATAGs when there is a DT?
> 
> I'm mainly pushing on this because adding "mem=" to the command-line in
> the DT file isn't a great solution; when people start using bootloaders
> that rewrite the DT to include the user-specified command-line, then every
> user is going to have to start specifying "mem=" in their command-lines.

Well, I see two options for our case:

	a) use the mem=448M at 0 in the DT so the gpu can get its memory
	b) upstream the chromeos changes to reserve gpu memory "on the fly" from 
the autodetected 512M (as it should be IMHO).

> > I've seen patches on the chromeos tree which try to reserve the gpu
> > memory on demand. While we are at it, what is the vmalloc=192M used
> > by most other boards for?
> 
> I'm not sure what vmalloc= does exactly. I somewhat doubt it's necessary
> until we have code that uses the GPU in mainline. The same goes for the
> /memreserve/ DT entries. I've been thinking of submitting a patch to
> remove this cruft, but haven't gotten around to it yet.

[PATCH v2 2/3] arm/dt: tegra: add dts file for paz00

[Grant Likely]

On Sun, Oct 30, 2011 at 09:39:37PM +0100, Marc Dietrich wrote:
> On Friday 28 October 2011 09:49:49 Stephen Warren wrote:
> > I also see a bunch of code to set up the memory
> > information from DT e.g. setup_machine_fdt()'s call to:
> > 
> > 	of_scan_flat_dt(early_init_dt_scan_memory, NULL);
> > 
> > ... but I assume that happens before the ATAGs are processed, and the
> > buggy ATAGs end up overriding the information in the DT file. And further,
> > I assume that specifying "mem=" on the command-line overrides that, thus
> > solving the problem.
> > 
> > It'd be awesome if you could validate this; the simplest way is probably
> > to:
> > 
> > a) Remove mem= from the command-line
> 
> I tested several variations. Without DT, the fixup can compensate a missing 
> mem entry in the kernel command line, but with a mem= from the kernel command 
> line, a fixup is not needed.
> 
> With DT, the command line specified from nvflash is ignored and the one from 
> DT comes into the game. If it is also missing there, system detects 512 MB 
> (which is physical right, but we cannot reserve memory for the gpu). The fixup 
> is indeed ignored in this case.

The /memreserve/ fields are supposed to allow you to do this.

> 
> > b) Modify arch/arm/kernel/setup.c:parse_tag_mem32() to do nothing;
> >    comment out the call to arm_add_memory()
> 
> I leave this out because the bootloader does not send memory info in the 
> ATAGS.
> 
> > c) Test booting, and check what RAM size the kernel thinks you have.
> 
> see above. RAM detection works, but it's not what we want ...
> 
> > If that works, then ATAGs are the problem. We probably need to modify the
> > core ARM code not to use memory ATAGs when there is a DT?
> > 
> > I'm mainly pushing on this because adding "mem=" to the command-line in
> > the DT file isn't a great solution; when people start using bootloaders
> > that rewrite the DT to include the user-specified command-line, then every
> > user is going to have to start specifying "mem=" in their command-lines.
> 
> Well, I see two options for our case:
> 
> 	a) use the mem=448M at 0 in the DT so the gpu can get its memory
> 	b) upstream the chromeos changes to reserve gpu memory "on the fly" from 
> the autodetected 512M (as it should be IMHO).

b) is the ideal.  a) is absolutely wrong.  /memreserve/ should fix the
gpu memory problem when not passing a mem= parameter.  If /memreserve/
isn't working, then I'd like to know why.

g.

[PATCH v2 2/3] arm/dt: tegra: add dts file for paz00

[Stephen Warren]

Marc Dietrich wrote at Sunday, October 30, 2011 2:40 PM:
> On Friday 28 October 2011 09:49:49 Stephen Warren wrote:
> > Marc Dietrich wrote at Friday, October 28, 2011 4:30 AM:
> > > Am Donnerstag, 27. Oktober 2011, 09:50:03 schrieb Stephen Warren:
> > > > Marc Dietrich wrote at Wednesday, October 26, 2011 1:59 PM:
> > > > > This adds a dts file for paz00. As a side effect, this also
> > > > > enables
> > > > > the embedded controller which controls the keyboard, touchpad,
> > > > > power,
> > > > > leds, and some other functions.
> > > >
> > > > ...
> > > >
> > > > > +++ b/arch/arm/boot/dts/tegra-paz00.dts
> > > > > @@ -0,0 +1,70 @@
> > > > > +/dts-v1/;
> > > > > +
> > > > > +/memreserve/ 0x1c000000 0x04000000;
> > > > > +/include/ "tegra20.dtsi"
> > > > > +
> > > > > +/ {
> > > > > +	model = "Toshiba AC100 / Dynabook AZ";
> > > > > +	compatible = "compal,paz00", "nvidia,tegra20";
> > > > > +
> > > > > +	chosen {
> > > > > +		bootargs = "mem=448 at 0 console=ttyS0,115200n8
> > > > > root=/dev/mmcblk1p1";
> > > >
> > > > You shouldn't need the mem= parameter here; it wasn't in your first
> > > > patch set.
> > > that's because I forgot it. Sorry, I didn't mentioned it in the
> > > changelog. I wonder why mem= is still needed.
> >
> > I wonder if this is some conflict between ATAGs and the DT-specified
> > memory node.
> >
> > As far as I can tell, the kernel's memory information typically comes
> > from ATAGs. Some boards override what's in the ATAGs in their machine
> > descriptor's fixup routine, e.g. see tegra_paz00_fixup(). Presumably,
> > this is because of buggy bootloaders sending incorrect memory information
> > in the ATAGs. Do you have any way to check the ATAGs that the bootloader
> > is sending? Probably, you could enable DEBUG_LL and using the low-level
> > debugging functions to dump some of that information to the UART early
> > during boot.
> 
> I got the ATAGS from /proc/atags and there is no memory entry there, only
> initrd and cmdline (which is the one from nvflash).
> 
> The machine also has a fixup routine, but it also boots without (I'm sure it
> was necessary in the past),
...
> I tested several variations. Without DT, the fixup can compensate a missing
> mem entry in the kernel command line, but with a mem= from the kernel command
> line, a fixup is not needed.

OK, that makes sense.

> With DT, the command line specified from nvflash is ignored and the one from
> DT comes into the game.

I assume you're using CONFIG_ARM_APPENDED_DTB but not CONFIG_ARM_ATAG_DTB_COMPAT.

> If it is also missing there, system detects 512 MB.

That makes sense; that's the value in the .dts file you posted.

> (which is physical right, but we cannot reserve memory for the gpu). The fixup
> is indeed ignored in this case.

It's not "ignored" as such.

When booting without DT, the machine descriptor in board-paz00.c is used,
since the descriptor is selected based on the machine ID in the descriptor,
and that descriptor includes:

	.fixup          = tegra_paz00_fixup,

... which causes that fixup function to be called.

When booting with DT, the machine descriptor in board-dt.c is used, since
the descriptor is selected based on the DT's overall compatible property,
and that descriptor doesn't refer to tegra_paz00_fixup() at all, so it's
not called.

> > b) Modify arch/arm/kernel/setup.c:parse_tag_mem32() to do nothing;
> >    comment out the call to arm_add_memory()
> 
> I leave this out because the bootloader does not send memory info in the
> ATAGS.
> 
> > c) Test booting, and check what RAM size the kernel thinks you have.
> 
> see above. RAM detection works, but it's not what we want ...

At this point, I'd argue that exposing the full 512M to the kernel /is/
what we want. There is no Tegra GPU support in the mainline kernel at
present. As such, I'd argue that we should give the entire RAM space to
the kernel to use. As and when we add GPU support to the kernel, we can
use an appropriate mechanism to take RAM away from the kernel for that
purpose.

So, I'm planning to remove all the /memreserve/ entries from the Tegra
.dts files as soon as I can find a minute to do so.

But, as Grant mentioned, the /memreserve/ .dts directive should work
right now to reserve memory. I'm not sure if you'd tried that and it didn't
work? If so, it'd be good to debug that just to make sure the mechanism
works, even if we don't intend to use it.

-- 
nvpublic

[PATCH v2 2/3] arm/dt: tegra: add dts file for paz00

[Marc Dietrich]

ok, lets bring this to an end.

On Monday 31 October 2011 09:09:13 Stephen Warren wrote:
> Marc Dietrich wrote at Sunday, October 30, 2011 2:40 PM:
> > On Friday 28 October 2011 09:49:49 Stephen Warren wrote:
> > > Marc Dietrich wrote at Friday, October 28, 2011 4:30 AM:
> > > > Am Donnerstag, 27. Oktober 2011, 09:50:03 schrieb Stephen Warren:
> > > > > Marc Dietrich wrote at Wednesday, October 26, 2011 1:59 PM:
> > > > > > This adds a dts file for paz00. As a side effect, this
> > > > > > also enables the embedded controller which controls the keyboard,
> > > > > > touchpad, power, leds, and some other functions.
> > > > > > ...
> > > > > > +++ b/arch/arm/boot/dts/tegra-paz00.dts
> > > > > > @@ -0,0 +1,70 @@
> > > > > > +/dts-v1/;
> > > > > > +
> > > > > > +/memreserve/ 0x1c000000 0x04000000;
> > > > > > +/include/ "tegra20.dtsi"
> > > > > > +
> > > > > > +/ {
> > > > > > +	model = "Toshiba AC100 / Dynabook AZ";
> > > > > > +	compatible = "compal,paz00", "nvidia,tegra20";
> > > > > > +
> > > > > > +	chosen {
> > > > > > +		bootargs = "mem=448 at 0 console=ttyS0,115200n8
> > > > > > root=/dev/mmcblk1p1";
> > > > > 
> > > > > You shouldn't need the mem= parameter here; it wasn't in
> > > > > your first patch set.
> > > > 
> > > > that's because I forgot it. Sorry, I didn't mentioned it in the
> > > > changelog. I wonder why mem= is still needed.
> > > 
> > > I wonder if this is some conflict between ATAGs and the DT-specified
> > > memory node.
> > > 
> > > As far as I can tell, the kernel's memory information typically
> > > comes from ATAGs. Some boards override what's in the ATAGs in their
> > > machine descriptor's fixup routine, e.g. see tegra_paz00_fixup().
> > > Presumably, this is because of buggy bootloaders sending incorrect
> > > memory information in the ATAGs. Do you have any way to check the ATAGs
> > > that the bootloader is sending? Probably, you could enable DEBUG_LL
> > > and using the low-level debugging functions to dump some of that
> > > information to the UART early during boot.
> > 
> > I got the ATAGS from /proc/atags and there is no memory entry there,
> > only
> > initrd and cmdline (which is the one from nvflash).
> > 
> > The machine also has a fixup routine, but it also boots without (I'm
> > sure it was necessary in the past),
> 
> ...
> 
> > I tested several variations. Without DT, the fixup can compensate a
> > missing mem entry in the kernel command line, but with a mem= from the
> > kernel command line, a fixup is not needed.
> 
> OK, that makes sense.
> 
> > With DT, the command line specified from nvflash is ignored and the one
> > from DT comes into the game.
> 
> I assume you're using CONFIG_ARM_APPENDED_DTB but not
> CONFIG_ARM_ATAG_DTB_COMPAT.
> > If it is also missing there, system detects 512 MB.

correct.

> That makes sense; that's the value in the .dts file you posted.
> 
> > (which is physical right, but we cannot reserve memory for the gpu). The
> > fixup is indeed ignored in this case.
> 
> It's not "ignored" as such.
> 
> When booting without DT, the machine descriptor in board-paz00.c is used,
> since the descriptor is selected based on the machine ID in the descriptor,
> and that descriptor includes:
> 
> 	.fixup          = tegra_paz00_fixup,
> 
> ... which causes that fixup function to be called.
> 
> When booting with DT, the machine descriptor in board-dt.c is used, since
> the descriptor is selected based on the DT's overall compatible property,
> and that descriptor doesn't refer to tegra_paz00_fixup() at all, so it's
> not called.

ok, I think I understood now. Thanks for the detailed explanation.

> >  ...
> >
> > > c) Test booting, and check what RAM size the kernel thinks you have.
> > 
> > see above. RAM detection works, but it's not what we want ...
> 
> At this point, I'd argue that exposing the full 512M to the kernel /is/
> what we want. There is no Tegra GPU support in the mainline kernel at
> present. As such, I'd argue that we should give the entire RAM space to
> the kernel to use. As and when we add GPU support to the kernel, we can
> use an appropriate mechanism to take RAM away from the kernel for that
> purpose.

sound fine. I guess the vmalloc is also due to some gpu requirements...

> So, I'm planning to remove all the /memreserve/ entries from the Tegra
> .dts files as soon as I can find a minute to do so.
> 
> But, as Grant mentioned, the /memreserve/ .dts directive should work
> right now to reserve memory. I'm not sure if you'd tried that and it didn't
> work? If so, it'd be good to debug that just to make sure the mechanism
> works, even if we don't intend to use it.

actually, it works as Grant said. For some reasons it didn't worked here when 
I tested it. Maybe I just catched a bad setup of linux-next/bootloader/kernel 
arguments.

Thanks for you patience with me...

Marc