Re: [PATCH v21 8/8] Documentation: dt: usable-memory and elfcorehdr nodes for arm64 kexec

Re: [PATCH v21 8/8] Documentation: dt: usable-memory and elfcorehdr nodes for arm64 kexec

[Thiago Jung Bauermann]

Hi,

Am Mittwoch, 06 Juli 2016, 16:52:26 schrieb AKASHI Takahiro:
> +linux,usable-memory
> +-------------------
> +
> +This property is set on PowerPC and arm64 by kexec-tools during kdump
> +to tell the crash kernel the base address of its reserved area of memory,
> and +the size. e.g.
> +
> +/ {
> +	chosen {
> +		linux,usable-memory = <0x9 0xf0000000 0x0 0x10000000>;
> +	};
> +};

Again, this description is wrong for PowerPC. See messages from myself and 
Michael Ellerman:

https://lists.infradead.org/pipermail/kexec/2016-June/016250.html

https://lists.infradead.org/pipermail/kexec/2016-June/016253.html

IMHO, it would be simpler if ARM used linux,usable-memory in the same way 
that PowerPC does, for consistency.

-- 
[]'s
Thiago Jung Bauermann
IBM Linux Technology Center

Re: [PATCH v21 8/8] Documentation: dt: usable-memory and elfcorehdr nodes for arm64 kexec

[AKASHI Takahiro]

On Wed, Jul 06, 2016 at 04:29:18PM -0300, Thiago Jung Bauermann wrote:
> Hi,
> 
> Am Mittwoch, 06 Juli 2016, 16:52:26 schrieb AKASHI Takahiro:
> > +linux,usable-memory
> > +-------------------
> > +
> > +This property is set on PowerPC and arm64 by kexec-tools during kdump
> > +to tell the crash kernel the base address of its reserved area of memory,
> > and +the size. e.g.
> > +
> > +/ {
> > +	chosen {
> > +		linux,usable-memory = <0x9 0xf0000000 0x0 0x10000000>;
> > +	};
> > +};
> 
> Again, this description is wrong for PowerPC. See messages from myself and 
> Michael Ellerman:
> 
> https://lists.infradead.org/pipermail/kexec/2016-June/016250.html
> 
> https://lists.infradead.org/pipermail/kexec/2016-June/016253.html

Oops, I must have missed your previous comments. Apologies.

Yes, I know that, and I used to implement the same functionality before.
It did work for dtb-based systems, but not for UEFI(ACPI)-based systems
because UEFI doesn't export memory regions information via a device tree,
but rather via ACPI table. So "/memory" node won't appear.
So I went back with "mem=" command line approach, and later this "/chosen/"
approach.

> IMHO, it would be simpler if ARM used linux,usable-memory in the same way 
> that PowerPC does, for consistency.

Well, this property won't conflict with per-"/memory" ones
if we take it that the former, if present, supersedes the latter.
Sophistic?
What about changing the name to usable-memory-limit?
(I know that you have another one, "memory-limit" though.)

Again, I would like to defer to arm64 maintainers.

Thanks,
-Takahiro AKASHI

> -- 
> []'s
> Thiago Jung Bauermann
> IBM Linux Technology Center
> 

Re: [PATCH v21 8/8] Documentation: dt: usable-memory and elfcorehdr nodes for arm64 kexec

[Thiago Jung Bauermann]

Am Donnerstag, 07 Juli 2016, 11:00:25 schrieb AKASHI Takahiro:
> On Wed, Jul 06, 2016 at 04:29:18PM -0300, Thiago Jung Bauermann wrote:
> > Hi,
> > 
> > Am Mittwoch, 06 Juli 2016, 16:52:26 schrieb AKASHI Takahiro:
> > > +linux,usable-memory
> > > +-------------------
> > > +
> > > +This property is set on PowerPC and arm64 by kexec-tools during kdump
> > > +to tell the crash kernel the base address of its reserved area of
> > > memory, and +the size. e.g.
> > > +
> > > +/ {
> > > +	chosen {
> > > +		linux,usable-memory = <0x9 0xf0000000 0x0 0x10000000>;
> > > +	};
> > > +};
> > 
> > Again, this description is wrong for PowerPC. See messages from myself
> > and Michael Ellerman:
> > 
> > https://lists.infradead.org/pipermail/kexec/2016-June/016250.html
> > 
> > https://lists.infradead.org/pipermail/kexec/2016-June/016253.html
> 
> Oops, I must have missed your previous comments. Apologies.

No problem.

> Yes, I know that, and I used to implement the same functionality before.
> It did work for dtb-based systems, but not for UEFI(ACPI)-based systems
> because UEFI doesn't export memory regions information via a device tree,
> but rather via ACPI table. So "/memory" node won't appear.
> So I went back with "mem=" command line approach, and later this
> "/chosen/" approach.

Ah, I didn't realize there could be dtb and UEFI systems.

> > IMHO, it would be simpler if ARM used linux,usable-memory in the same
> > way
> > that PowerPC does, for consistency.
> 
> Well, this property won't conflict with per-"/memory" ones
> if we take it that the former, if present, supersedes the latter.
> Sophistic?
> What about changing the name to usable-memory-limit?
> (I know that you have another one, "memory-limit" though.)
> 
> Again, I would like to defer to arm64 maintainers.

My personal opinion is that having a property with a different name would be 
less confusing, but it's not a strong opinion.

I would suggest calling it usable-memory-range, but I'm fine with whatever 
is decided by the maintainers.

-- 
[]'s
Thiago Jung Bauermann
IBM Linux Technology Center