Re: [PATCH v24 9/9] Documentation: dt: chosen properties for arm64 kdump

[Mark Rutland]

Hi Rob,

Reviving an old thread -- "rock" and "hard place" come to mind.

On Fri, Aug 19, 2016 at 08:26:41AM -0500, Rob Herring wrote:
> On Tue, Aug 09, 2016 at 10:57:47AM +0900, AKASHI Takahiro wrote:
> > From: James Morse 

> > +linux,usable-memory-range
> > +-
> > +
> > +This property (currently used only on arm64) holds the memory range,
> > +the base address and the size, which can be used as system ram on
> > +the *current* kernel. Note that, if this property is present, any memory
> > +regions under "memory" nodes in DT blob or ones marked as "conventional
> > +memory" in EFI memory map should be ignored.
> > +e.g.
> > +
> > +/ {
> > +   chosen {
> > +   linux,usable-memory-range = <0x9 0xf000 0x0 0x1000>;
> > +   };
> > +};
> 
> I've read the discussion on this. I think you should use the existing 
> linux,usable-memory property in the memory nodes. If UEFI systems don't 
> have memory nodes, then you can find an UEFI way to describe this. DT is 
> not the dumping ground for what doesn't fit in UEFI. How do x86 systems 
> work?

Having looked at the proposals, I'm personally much keener on the approach
above (modulo naming and wording) than trying to bolt memory nodes onto a UEFI
system, or using reserved-memory to describe the inverse of the allowable
range.

I completely agree that we want one solution for DT-only and DT+UEFI.

While those approaches reuse existing infrastructure, they end up creating more
work, and I believe that they create more scope for painful problems. As kdump
is already a constrained case, I think that it's reasonable to have a
linux-specific property as above.

I also think we need to figure out how we expect this to work for the
kexec_file_load case, as that has a criticial impact on the above (e.g. what's
preferable out of cmdline options vs dt properties).

Can we try to sync at connect to discuss this?

Thanks,
Mark.

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Re: [PATCH v24 9/9] Documentation: dt: chosen properties for arm64 kdump

[AKASHI Takahiro]

Rob,

On Wed, Aug 31, 2016 at 02:02:16PM +0900, AKASHI Takahiro wrote:
> On Wed, Aug 31, 2016 at 08:45:46AM +0900, AKASHI Takahiro wrote:
> > Rob,
> > 
> > On Tue, Aug 30, 2016 at 11:34:10AM -0500, Rob Herring wrote:
> > > On Sun, Aug 21, 2016 at 11:28 PM, AKASHI Takahiro
> > >  wrote:
> > > > Rob,
> > > > [Cc: Mark]
> > > >
> > > > On Fri, Aug 19, 2016 at 08:26:41AM -0500, Rob Herring wrote:
> > > >> On Tue, Aug 09, 2016 at 10:57:47AM +0900, AKASHI Takahiro wrote:
> > > >> > From: James Morse 
> > > >> >
> > > >> > Add documentation for
> > > >> > linux,crashkernel-base and crashkernel-size,
> > > >> > linux,usable-memory-range, and
> > > >> > linux,elfcorehdr
> > > >> > used by arm64 kexec/kdump to decribe the kdump reserved area, and
> > > >> > the elfcorehdr's location within it.
> > > >> >
> > > >> > Signed-off-by: James Morse 
> > > >> > [takahiro.aka...@linaro.org:
> > > >> > renamed "usable-memory" to "usable-memory-range",
> > > >> > added "linux,crashkernel-base" and "-size" ]
> > > >> > Signed-off-by: AKASHI Takahiro 
> > > >> > ---
> > > >> >  Documentation/devicetree/bindings/chosen.txt | 50 
> > > >> > 
> > > >> >  1 file changed, 50 insertions(+)
> > > >> >
> > > >> > diff --git a/Documentation/devicetree/bindings/chosen.txt 
> > > >> > b/Documentation/devicetree/bindings/chosen.txt
> > > >> > index 6ae9d82..236188a 100644
> > > >> > --- a/Documentation/devicetree/bindings/chosen.txt
> > > >> > +++ b/Documentation/devicetree/bindings/chosen.txt
> > > >> > @@ -52,3 +52,53 @@ This property is set (currently only on PowerPC, 
> > > >> > and only needed on
> > > >> >  book3e) by some versions of kexec-tools to tell the new kernel that 
> > > >> > it
> > > >> >  is being booted by kexec, as the booting environment may differ 
> > > >> > (e.g.
> > > >> >  a different secondary CPU release mechanism)
> > > >> > +
> > > >> > +linux,crashkernel-base
> > > >> > +linux,crashkernel-size
> > > >> > +--
> > > >> > +These properties (currently used on PowerPC and arm64) indicates
> > > >> > +the base address and the size, respectively, of the reserved memory
> > > >> > +range for crash dump kernel.
> > > >> > +e.g.
> > > >> > +
> > > >> > +/ {
> > > >> > +   chosen {
> > > >> > +   linux,crashkernel-base = <0x9 0xf000>;
> > > >> > +   linux,crashkernel-size = <0x0 0x1000>;
> > > >> > +   };
> > > >> > +};
> > > >> > +
> > > >> > +linux,usable-memory-range
> > > >> > +-
> > > >> > +
> > > >> > +This property (currently used only on arm64) holds the memory range,
> > > >> > +the base address and the size, which can be used as system ram on
> > > >> > +the *current* kernel. Note that, if this property is present, any 
> > > >> > memory
> > > >> > +regions under "memory" nodes in DT blob or ones marked as 
> > > >> > "conventional
> > > >> > +memory" in EFI memory map should be ignored.
> > > >> > +e.g.
> > > >> > +
> > > >> > +/ {
> > > >> > +   chosen {
> > > >> > +   linux,usable-memory-range = <0x9 0xf000 0x0 
> > > >> > 0x1000>;
> > > >> > +   };
> > > >> > +};
> > > >>
> > > >> I've read the discussion on this. I think you should use the existing
> > > >> linux,usable-memory property in the memory nodes. If UEFI systems don't
> > > >> have memory nodes, then you can find an UEFI way to describe this. DT 
> > > >> is
> > > >> not the dumping ground for what doesn't fit in UEFI. How do x86 systems
> > > >> work?
> > > >
> > > > Kdump for x86 passes the range of usable memory to crash dump kernel
> > > > either via:
> > > > (a) "memmap=nn@ss" command line parameter, or
> > > > (b) faked BIOS e820 map (a sort of memory map table)
> > > >
> > > > (a) was rejected by Mark [1], and (b) is x86-specific.
> > > >
> > > > I believe that my approach is better because it works in the same way
> > > > either on UEFI systems or DT-based systems.
> > > 
> > > So we have a new way for both UEFI and DT. If UEFI folks can't come up
> > > with a standard way to do things in the UEFI standard, then we just
> > > dump them into DT?
> > 
> > No, I don't think so.
> > According to "Documentation/devicetree/bindings/chosen.txt,
> >   "The chosen node does not represent a real device, but serves as a place
> >for passing data between firmware and the operating system, like boot
> >arguments."
> > 
> > Since kexec/dump is some sort of boot loader, it all makes sense to
> > add a new property as an interface from the old kernel(kexec/dump)
> > to the new kernel. So my approach doesn't break any DT rules.
> > 
> > Please note that, even on UEFI/APCI systems, there are already a few
> > properties used under /chosen, like "linux,uefi-system-table" and 
> > "linux,mmap-*."
> > (Those properties are currently *not* defined in this document, though.)
> > 
> > > I'd rather see alignment with existing DT 

Re: [PATCH v24 9/9] Documentation: dt: chosen properties for arm64 kdump

[AKASHI Takahiro]

On Wed, Aug 31, 2016 at 08:45:46AM +0900, AKASHI Takahiro wrote:
> Rob,
> 
> On Tue, Aug 30, 2016 at 11:34:10AM -0500, Rob Herring wrote:
> > On Sun, Aug 21, 2016 at 11:28 PM, AKASHI Takahiro
> >  wrote:
> > > Rob,
> > > [Cc: Mark]
> > >
> > > On Fri, Aug 19, 2016 at 08:26:41AM -0500, Rob Herring wrote:
> > >> On Tue, Aug 09, 2016 at 10:57:47AM +0900, AKASHI Takahiro wrote:
> > >> > From: James Morse 
> > >> >
> > >> > Add documentation for
> > >> > linux,crashkernel-base and crashkernel-size,
> > >> > linux,usable-memory-range, and
> > >> > linux,elfcorehdr
> > >> > used by arm64 kexec/kdump to decribe the kdump reserved area, and
> > >> > the elfcorehdr's location within it.
> > >> >
> > >> > Signed-off-by: James Morse 
> > >> > [takahiro.aka...@linaro.org:
> > >> > renamed "usable-memory" to "usable-memory-range",
> > >> > added "linux,crashkernel-base" and "-size" ]
> > >> > Signed-off-by: AKASHI Takahiro 
> > >> > ---
> > >> >  Documentation/devicetree/bindings/chosen.txt | 50 
> > >> > 
> > >> >  1 file changed, 50 insertions(+)
> > >> >
> > >> > diff --git a/Documentation/devicetree/bindings/chosen.txt 
> > >> > b/Documentation/devicetree/bindings/chosen.txt
> > >> > index 6ae9d82..236188a 100644
> > >> > --- a/Documentation/devicetree/bindings/chosen.txt
> > >> > +++ b/Documentation/devicetree/bindings/chosen.txt
> > >> > @@ -52,3 +52,53 @@ This property is set (currently only on PowerPC, 
> > >> > and only needed on
> > >> >  book3e) by some versions of kexec-tools to tell the new kernel that it
> > >> >  is being booted by kexec, as the booting environment may differ (e.g.
> > >> >  a different secondary CPU release mechanism)
> > >> > +
> > >> > +linux,crashkernel-base
> > >> > +linux,crashkernel-size
> > >> > +--
> > >> > +These properties (currently used on PowerPC and arm64) indicates
> > >> > +the base address and the size, respectively, of the reserved memory
> > >> > +range for crash dump kernel.
> > >> > +e.g.
> > >> > +
> > >> > +/ {
> > >> > +   chosen {
> > >> > +   linux,crashkernel-base = <0x9 0xf000>;
> > >> > +   linux,crashkernel-size = <0x0 0x1000>;
> > >> > +   };
> > >> > +};
> > >> > +
> > >> > +linux,usable-memory-range
> > >> > +-
> > >> > +
> > >> > +This property (currently used only on arm64) holds the memory range,
> > >> > +the base address and the size, which can be used as system ram on
> > >> > +the *current* kernel. Note that, if this property is present, any 
> > >> > memory
> > >> > +regions under "memory" nodes in DT blob or ones marked as 
> > >> > "conventional
> > >> > +memory" in EFI memory map should be ignored.
> > >> > +e.g.
> > >> > +
> > >> > +/ {
> > >> > +   chosen {
> > >> > +   linux,usable-memory-range = <0x9 0xf000 0x0 
> > >> > 0x1000>;
> > >> > +   };
> > >> > +};
> > >>
> > >> I've read the discussion on this. I think you should use the existing
> > >> linux,usable-memory property in the memory nodes. If UEFI systems don't
> > >> have memory nodes, then you can find an UEFI way to describe this. DT is
> > >> not the dumping ground for what doesn't fit in UEFI. How do x86 systems
> > >> work?
> > >
> > > Kdump for x86 passes the range of usable memory to crash dump kernel
> > > either via:
> > > (a) "memmap=nn@ss" command line parameter, or
> > > (b) faked BIOS e820 map (a sort of memory map table)
> > >
> > > (a) was rejected by Mark [1], and (b) is x86-specific.
> > >
> > > I believe that my approach is better because it works in the same way
> > > either on UEFI systems or DT-based systems.
> > 
> > So we have a new way for both UEFI and DT. If UEFI folks can't come up
> > with a standard way to do things in the UEFI standard, then we just
> > dump them into DT?
> 
> No, I don't think so.
> According to "Documentation/devicetree/bindings/chosen.txt,
>   "The chosen node does not represent a real device, but serves as a place
>for passing data between firmware and the operating system, like boot
>arguments."
> 
> Since kexec/dump is some sort of boot loader, it all makes sense to
> add a new property as an interface from the old kernel(kexec/dump)
> to the new kernel. So my approach doesn't break any DT rules.
> 
> Please note that, even on UEFI/APCI systems, there are already a few
> properties used under /chosen, like "linux,uefi-system-table" and 
> "linux,mmap-*."
> (Those properties are currently *not* defined in this document, though.)
> 
> > I'd rather see alignment with existing DT systems
> > (PPC) and in particular the tools.
> 
> I'm not sure what you mean here, but I guess:
> 1) On DT-only systems, we should follow the way that PPC does.
>(That is, adding "usable-memory" property to each "memory" node.)
> 2) On UEFI/ACPI system, we must invent a new own way for our purpose
>because, as I 

Re: [PATCH v24 9/9] Documentation: dt: chosen properties for arm64 kdump

[AKASHI Takahiro]

Rob,

On Tue, Aug 30, 2016 at 11:34:10AM -0500, Rob Herring wrote:
> On Sun, Aug 21, 2016 at 11:28 PM, AKASHI Takahiro
>  wrote:
> > Rob,
> > [Cc: Mark]
> >
> > On Fri, Aug 19, 2016 at 08:26:41AM -0500, Rob Herring wrote:
> >> On Tue, Aug 09, 2016 at 10:57:47AM +0900, AKASHI Takahiro wrote:
> >> > From: James Morse 
> >> >
> >> > Add documentation for
> >> > linux,crashkernel-base and crashkernel-size,
> >> > linux,usable-memory-range, and
> >> > linux,elfcorehdr
> >> > used by arm64 kexec/kdump to decribe the kdump reserved area, and
> >> > the elfcorehdr's location within it.
> >> >
> >> > Signed-off-by: James Morse 
> >> > [takahiro.aka...@linaro.org:
> >> > renamed "usable-memory" to "usable-memory-range",
> >> > added "linux,crashkernel-base" and "-size" ]
> >> > Signed-off-by: AKASHI Takahiro 
> >> > ---
> >> >  Documentation/devicetree/bindings/chosen.txt | 50 
> >> > 
> >> >  1 file changed, 50 insertions(+)
> >> >
> >> > diff --git a/Documentation/devicetree/bindings/chosen.txt 
> >> > b/Documentation/devicetree/bindings/chosen.txt
> >> > index 6ae9d82..236188a 100644
> >> > --- a/Documentation/devicetree/bindings/chosen.txt
> >> > +++ b/Documentation/devicetree/bindings/chosen.txt
> >> > @@ -52,3 +52,53 @@ This property is set (currently only on PowerPC, and 
> >> > only needed on
> >> >  book3e) by some versions of kexec-tools to tell the new kernel that it
> >> >  is being booted by kexec, as the booting environment may differ (e.g.
> >> >  a different secondary CPU release mechanism)
> >> > +
> >> > +linux,crashkernel-base
> >> > +linux,crashkernel-size
> >> > +--
> >> > +These properties (currently used on PowerPC and arm64) indicates
> >> > +the base address and the size, respectively, of the reserved memory
> >> > +range for crash dump kernel.
> >> > +e.g.
> >> > +
> >> > +/ {
> >> > +   chosen {
> >> > +   linux,crashkernel-base = <0x9 0xf000>;
> >> > +   linux,crashkernel-size = <0x0 0x1000>;
> >> > +   };
> >> > +};
> >> > +
> >> > +linux,usable-memory-range
> >> > +-
> >> > +
> >> > +This property (currently used only on arm64) holds the memory range,
> >> > +the base address and the size, which can be used as system ram on
> >> > +the *current* kernel. Note that, if this property is present, any memory
> >> > +regions under "memory" nodes in DT blob or ones marked as "conventional
> >> > +memory" in EFI memory map should be ignored.
> >> > +e.g.
> >> > +
> >> > +/ {
> >> > +   chosen {
> >> > +   linux,usable-memory-range = <0x9 0xf000 0x0 0x1000>;
> >> > +   };
> >> > +};
> >>
> >> I've read the discussion on this. I think you should use the existing
> >> linux,usable-memory property in the memory nodes. If UEFI systems don't
> >> have memory nodes, then you can find an UEFI way to describe this. DT is
> >> not the dumping ground for what doesn't fit in UEFI. How do x86 systems
> >> work?
> >
> > Kdump for x86 passes the range of usable memory to crash dump kernel
> > either via:
> > (a) "memmap=nn@ss" command line parameter, or
> > (b) faked BIOS e820 map (a sort of memory map table)
> >
> > (a) was rejected by Mark [1], and (b) is x86-specific.
> >
> > I believe that my approach is better because it works in the same way
> > either on UEFI systems or DT-based systems.
> 
> So we have a new way for both UEFI and DT. If UEFI folks can't come up
> with a standard way to do things in the UEFI standard, then we just
> dump them into DT?

No, I don't think so.
According to "Documentation/devicetree/bindings/chosen.txt,
  "The chosen node does not represent a real device, but serves as a place
   for passing data between firmware and the operating system, like boot
   arguments."

Since kexec/dump is some sort of boot loader, it all makes sense to
add a new property as an interface from the old kernel(kexec/dump)
to the new kernel. So my approach doesn't break any DT rules.

Please note that, even on UEFI/APCI systems, there are already a few
properties used under /chosen, like "linux,uefi-system-table" and 
"linux,mmap-*."
(Those properties are currently *not* defined in this document, though.)

> I'd rather see alignment with existing DT systems
> (PPC) and in particular the tools.

I'm not sure what you mean here, but I guess:
1) On DT-only systems, we should follow the way that PPC does.
   (That is, adding "usable-memory" property to each "memory" node.)
2) On UEFI/ACPI system, we must invent a new own way for our purpose
   because, as I said before, there is no standard, but x86-specific way. 

Is this what you want to do?

If so,
do you agree to my approach of adding "linux,usable-memory-range" property
to /chosen *for UEFI/ACPI use*?

Thanks,
-Takahiro AKASHI

> Rob

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Re: [PATCH v24 9/9] Documentation: dt: chosen properties for arm64 kdump

[Rob Herring]

On Sun, Aug 21, 2016 at 11:28 PM, AKASHI Takahiro
 wrote:
> Rob,
> [Cc: Mark]
>
> On Fri, Aug 19, 2016 at 08:26:41AM -0500, Rob Herring wrote:
>> On Tue, Aug 09, 2016 at 10:57:47AM +0900, AKASHI Takahiro wrote:
>> > From: James Morse 
>> >
>> > Add documentation for
>> > linux,crashkernel-base and crashkernel-size,
>> > linux,usable-memory-range, and
>> > linux,elfcorehdr
>> > used by arm64 kexec/kdump to decribe the kdump reserved area, and
>> > the elfcorehdr's location within it.
>> >
>> > Signed-off-by: James Morse 
>> > [takahiro.aka...@linaro.org:
>> > renamed "usable-memory" to "usable-memory-range",
>> > added "linux,crashkernel-base" and "-size" ]
>> > Signed-off-by: AKASHI Takahiro 
>> > ---
>> >  Documentation/devicetree/bindings/chosen.txt | 50 
>> > 
>> >  1 file changed, 50 insertions(+)
>> >
>> > diff --git a/Documentation/devicetree/bindings/chosen.txt 
>> > b/Documentation/devicetree/bindings/chosen.txt
>> > index 6ae9d82..236188a 100644
>> > --- a/Documentation/devicetree/bindings/chosen.txt
>> > +++ b/Documentation/devicetree/bindings/chosen.txt
>> > @@ -52,3 +52,53 @@ This property is set (currently only on PowerPC, and 
>> > only needed on
>> >  book3e) by some versions of kexec-tools to tell the new kernel that it
>> >  is being booted by kexec, as the booting environment may differ (e.g.
>> >  a different secondary CPU release mechanism)
>> > +
>> > +linux,crashkernel-base
>> > +linux,crashkernel-size
>> > +--
>> > +These properties (currently used on PowerPC and arm64) indicates
>> > +the base address and the size, respectively, of the reserved memory
>> > +range for crash dump kernel.
>> > +e.g.
>> > +
>> > +/ {
>> > +   chosen {
>> > +   linux,crashkernel-base = <0x9 0xf000>;
>> > +   linux,crashkernel-size = <0x0 0x1000>;
>> > +   };
>> > +};
>> > +
>> > +linux,usable-memory-range
>> > +-
>> > +
>> > +This property (currently used only on arm64) holds the memory range,
>> > +the base address and the size, which can be used as system ram on
>> > +the *current* kernel. Note that, if this property is present, any memory
>> > +regions under "memory" nodes in DT blob or ones marked as "conventional
>> > +memory" in EFI memory map should be ignored.
>> > +e.g.
>> > +
>> > +/ {
>> > +   chosen {
>> > +   linux,usable-memory-range = <0x9 0xf000 0x0 0x1000>;
>> > +   };
>> > +};
>>
>> I've read the discussion on this. I think you should use the existing
>> linux,usable-memory property in the memory nodes. If UEFI systems don't
>> have memory nodes, then you can find an UEFI way to describe this. DT is
>> not the dumping ground for what doesn't fit in UEFI. How do x86 systems
>> work?
>
> Kdump for x86 passes the range of usable memory to crash dump kernel
> either via:
> (a) "memmap=nn@ss" command line parameter, or
> (b) faked BIOS e820 map (a sort of memory map table)
>
> (a) was rejected by Mark [1], and (b) is x86-specific.
>
> I believe that my approach is better because it works in the same way
> either on UEFI systems or DT-based systems.

So we have a new way for both UEFI and DT. If UEFI folks can't come up
with a standard way to do things in the UEFI standard, then we just
dump them into DT? I'd rather see alignment with existing DT systems
(PPC) and in particular the tools.

Rob

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Re: [PATCH v24 9/9] Documentation: dt: chosen properties for arm64 kdump

[AKASHI Takahiro]

Rob,
[Cc: Mark]

On Fri, Aug 19, 2016 at 08:26:41AM -0500, Rob Herring wrote:
> On Tue, Aug 09, 2016 at 10:57:47AM +0900, AKASHI Takahiro wrote:
> > From: James Morse 
> > 
> > Add documentation for
> > linux,crashkernel-base and crashkernel-size,
> > linux,usable-memory-range, and
> > linux,elfcorehdr
> > used by arm64 kexec/kdump to decribe the kdump reserved area, and
> > the elfcorehdr's location within it.
> > 
> > Signed-off-by: James Morse 
> > [takahiro.aka...@linaro.org:
> > renamed "usable-memory" to "usable-memory-range",
> > added "linux,crashkernel-base" and "-size" ]
> > Signed-off-by: AKASHI Takahiro 
> > ---
> >  Documentation/devicetree/bindings/chosen.txt | 50 
> > 
> >  1 file changed, 50 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/chosen.txt 
> > b/Documentation/devicetree/bindings/chosen.txt
> > index 6ae9d82..236188a 100644
> > --- a/Documentation/devicetree/bindings/chosen.txt
> > +++ b/Documentation/devicetree/bindings/chosen.txt
> > @@ -52,3 +52,53 @@ This property is set (currently only on PowerPC, and 
> > only needed on
> >  book3e) by some versions of kexec-tools to tell the new kernel that it
> >  is being booted by kexec, as the booting environment may differ (e.g.
> >  a different secondary CPU release mechanism)
> > +
> > +linux,crashkernel-base
> > +linux,crashkernel-size
> > +--
> > +These properties (currently used on PowerPC and arm64) indicates
> > +the base address and the size, respectively, of the reserved memory
> > +range for crash dump kernel.
> > +e.g.
> > +
> > +/ {
> > +   chosen {
> > +   linux,crashkernel-base = <0x9 0xf000>;
> > +   linux,crashkernel-size = <0x0 0x1000>;
> > +   };
> > +};
> > +
> > +linux,usable-memory-range
> > +-
> > +
> > +This property (currently used only on arm64) holds the memory range,
> > +the base address and the size, which can be used as system ram on
> > +the *current* kernel. Note that, if this property is present, any memory
> > +regions under "memory" nodes in DT blob or ones marked as "conventional
> > +memory" in EFI memory map should be ignored.
> > +e.g.
> > +
> > +/ {
> > +   chosen {
> > +   linux,usable-memory-range = <0x9 0xf000 0x0 0x1000>;
> > +   };
> > +};
> 
> I've read the discussion on this. I think you should use the existing 
> linux,usable-memory property in the memory nodes. If UEFI systems don't 
> have memory nodes, then you can find an UEFI way to describe this. DT is 
> not the dumping ground for what doesn't fit in UEFI. How do x86 systems 
> work?

Kdump for x86 passes the range of usable memory to crash dump kernel
either via:
(a) "memmap=nn@ss" command line parameter, or
(b) faked BIOS e820 map (a sort of memory map table)

(a) was rejected by Mark [1], and (b) is x86-specific.

I believe that my approach is better because it works in the same way
either on UEFI systems or DT-based systems.

[1] 
http://lists.infradead.org/pipermail/linux-arm-kernel/2016-January/400122.html

Thanks,
-Takahiro AKASHI

> Rob

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Re: [PATCH v24 9/9] Documentation: dt: chosen properties for arm64 kdump

[Rob Herring]

On Tue, Aug 09, 2016 at 10:57:47AM +0900, AKASHI Takahiro wrote:
> From: James Morse 
> 
> Add documentation for
>   linux,crashkernel-base and crashkernel-size,
>   linux,usable-memory-range, and
>   linux,elfcorehdr
> used by arm64 kexec/kdump to decribe the kdump reserved area, and
> the elfcorehdr's location within it.
> 
> Signed-off-by: James Morse 
> [takahiro.aka...@linaro.org:
> renamed "usable-memory" to "usable-memory-range",
> added "linux,crashkernel-base" and "-size" ]
> Signed-off-by: AKASHI Takahiro 
> ---
>  Documentation/devicetree/bindings/chosen.txt | 50 
> 
>  1 file changed, 50 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/chosen.txt 
> b/Documentation/devicetree/bindings/chosen.txt
> index 6ae9d82..236188a 100644
> --- a/Documentation/devicetree/bindings/chosen.txt
> +++ b/Documentation/devicetree/bindings/chosen.txt
> @@ -52,3 +52,53 @@ This property is set (currently only on PowerPC, and only 
> needed on
>  book3e) by some versions of kexec-tools to tell the new kernel that it
>  is being booted by kexec, as the booting environment may differ (e.g.
>  a different secondary CPU release mechanism)
> +
> +linux,crashkernel-base
> +linux,crashkernel-size
> +--
> +These properties (currently used on PowerPC and arm64) indicates
> +the base address and the size, respectively, of the reserved memory
> +range for crash dump kernel.
> +e.g.
> +
> +/ {
> + chosen {
> + linux,crashkernel-base = <0x9 0xf000>;
> + linux,crashkernel-size = <0x0 0x1000>;
> + };
> +};
> +
> +linux,usable-memory-range
> +-
> +
> +This property (currently used only on arm64) holds the memory range,
> +the base address and the size, which can be used as system ram on
> +the *current* kernel. Note that, if this property is present, any memory
> +regions under "memory" nodes in DT blob or ones marked as "conventional
> +memory" in EFI memory map should be ignored.
> +e.g.
> +
> +/ {
> + chosen {
> + linux,usable-memory-range = <0x9 0xf000 0x0 0x1000>;
> + };
> +};

I've read the discussion on this. I think you should use the existing 
linux,usable-memory property in the memory nodes. If UEFI systems don't 
have memory nodes, then you can find an UEFI way to describe this. DT is 
not the dumping ground for what doesn't fit in UEFI. How do x86 systems 
work?

Rob

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