Re: [PULL v2 40/61] hw/acpi: Update GED _EVT method AML with CPU scan

[Igor Mammedov <imammedo@redhat.com>]

On Mon, 14 Oct 2024 20:05:58 +0000
Salil Mehta <salil.mehta@huawei.com> wrote:

> Hi Igor,
> 
> >  From: qemu-devel-bounces+salil.mehta=huawei.com@nongnu.org <qemu-
> >  devel-bounces+salil.mehta=huawei.com@nongnu.org> On Behalf Of Igor
> >  Mammedov
> >  Sent: Monday, October 14, 2024 10:38 AM
> >  
> >  On Mon, 14 Oct 2024 16:52:55 +0800
> >  maobibo <maobibo@loongson.cn> wrote:
> >    
> >  > Hi Salil,
> >  >
> >  > When I debug cpu hotplug on LoongArch system, It reports error like this:
> >  >      ACPI BIOS Error (bug): Could not resolve symbol [\_SB.GED.CSCN],
> >  > AE_NOT_FOUND
> >  >      ACPI Error: Aborting method \_SB.GED._EVT due to previous error
> >  > (AE_NOT_FOUND)
> >  >      acpi-ged ACPI0013:00: IRQ method execution failed
> >  >
> >  >
> >  > With this patch, GED CPU call method is "\\_SB.GED.CSCN", however in
> >  > function build_cpus_aml(), its method name is "\\_SB.CPUS.CSCN".
> >  >      method = aml_method(event_handler_method, 0,  
> >  AML_NOTSERIALIZED);  
> >  >      aml_append(method, aml_call0("\\_SB.CPUS." CPU_SCAN_METHOD));
> >  >      aml_append(table, method);
> >  >
> >  > It seems that CPU scanning method name is not consistent between
> >  > function build_cpus_aml() and build_ged_aml().
> >  >
> >  > Regards
> >  > Bibo Mao
> >  >
> >  > On 2024/7/23 下午6:59, Michael S. Tsirkin wrote:  
> >  > > From: Salil Mehta <salil.mehta@huawei.com>
> >  > >
> >  > > OSPM evaluates _EVT method to map the event. The CPU hotplug  
> >  event  
> >  > > eventually results in start of the CPU scan. Scan figures out the
> >  > > CPU and the kind of
> >  > > event(plug/unplug) and notifies it back to the guest. Update the GED
> >  > > AML _EVT method with the call to method \\_SB.CPUS.CSCN (via
> >  > > \\_SB.GED.CSCN)
> >  > >
> >  > > Architecture specific code [1] might initialize its CPUs AML code by
> >  > > calling common function build_cpus_aml() like below for ARM:
> >  > >
> >  > > build_cpus_aml(scope, ms, opts, xx_madt_cpu_entry,  
> >  memmap[VIRT_CPUHP_ACPI].base,  
> >  > >                 "\\_SB", "\\_SB.GED.CSCN", AML_SYSTEM_MEMORY);  
> >  
> >  it should be \\_SB.CPUS.CSCN  
> 
> 
> I guess we are getting back to where we started then?
> 
> https://lore.kernel.org/qemu-devel/20240706162845.3baf5568@imammedo.users.ipa.redhat.com/
> 

Indeed, CSCN in name had me confused,
perhaps it would be better to rename that something else.
maybe something like s/_SB.GED.CSCN/_SB.GED.ECPU/

> Excerpt from above discussion and your suggestion:
> [...]
> 
> I don't particularly like exposing cpu hotplug internals for outside code
> and then making that code do plumbing hoping that nothing will explode
> in the future.
> 
> build_cpus_aml() takes event_handler_method to create a method that
> can be called by platform. What I suggest is to call that method here
> instead of trying to expose CPU hotplug internals and manually building
> call path here.
> aka:
>   build_cpus_aml(event_handler_method = PATH_TO_GED_DEVICE.CSCN)
> and then call here 
>   aml_append(if_ctx, aml_call0(CSCN));
> which will call  CSCN in GED scope, that was be populated by
> build_cpus_aml() to do cpu scan properly without need to expose
> cpu hotplug internal names and then trying to fixup conflicts caused by that.
> 
> PS:
> we should do the same for memory hotplug, we see in context above
> 
> [...]
> 
> 
> Solution:
> I've avoided above error in different way and keeping exactly what you
> suggested \_SB.PATH_TO_GED_DEVICE.CSCN i.e. \_SB.GED.CSCN
> Please have a look:
> 
> https://lore.kernel.org/qemu-devel/20241009031815.250096-16-salil.mehta@huawei.com/
> 
> Many thanks!
> 
> 
> Best regards
> Salil.
>