Re: [RFC PATCH] xen/arm: arm32: Enable smpboot on Arm32 based systems

[Julien Grall <julien@xxxxxxx>]

Hi Ayan,

On 03/05/2023 17:49, Ayan Kumar Halder wrote:
> On 03/05/2023 08:40, Julien Grall wrote:
> > Hi,
> Hi Julien,
> > Title: Did you mean "Enable spin table"?
> Yes, that would be more concrete.
> > On 02/05/2023 11:58, Ayan Kumar Halder wrote:
> > > On some of the Arm32 based systems (eg Cortex-R52), smpboot is 
> > > supported.
> > Same here.
> Yes
> > > In these systems PSCI may not always be supported. In case of 
> > > Cortex-R52, there
> > > is no EL3 or secure mode. Thus, PSCI is not supported as it requires 
> > > EL3.
> > > Thus, we use 'spin-table' mechanism to boot the secondary cpus. The 
> > > primary
> > > cpu provides the startup address of the secondary cores. This address is
> > > provided using the 'cpu-release-addr' property.
> > >
> > > To support smpboot, we have copied the code from 
> > > xen/arch/arm/arm64/smpboot.c
> > I would rather prefer if we don't duplicate the code but instead move 
> > the logic in common code.
> Ack
> > > with the following changes :-
> > >
> > > 1. 'enable-method' is an optional property. Refer to the comment in
> > > https://www.kernel.org/doc/Documentation/devicetree/bindings/arm/cpus.yaml
> > > "      # On ARM 32-bit systems this property is optional"
> > Looking at this list, "spin-table" doesn't seem to be supported
> > for 32-bit systems. 
> However, looking at 
> https://developer.arm.com/documentation/den0013/d/Multi-core-processors/Booting-SMP-systems/SMP-boot-in-Linux , it seems "spin-table" is a valid boot mechanism for Armv7 cpus.
I am not able to find the associated code in Linux 32-bit. Do you have 
any pointer?
> > Can you point me to the discussion/patch where this would be added?
> Actually, this is the first discussion I am having with regards to 
> adding a "spin-table" support on Arm32.
I was asking for the discussion on the Device-Tree/Linux ML or code.
I don't really want to do a "spin-table" support if this is not even 
supported in Linux.
Cheers,

--
Julien Grall