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Re: [PATCH for-5.0 8/8] acpi: cpuhp: spec: document procedure for enabli
Re: [PATCH for-5.0 8/8] acpi: cpuhp: spec: document procedure for enabling modern CPU hotplug
Fri, 6 Dec 2019 16:06:24 +0100
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1
On 12/06/19 14:49, Igor Mammedov wrote:
> On Thu, 5 Dec 2019 15:07:53 +0100
> Laszlo Ersek <address@hidden> wrote:
>> On 12/04/19 18:05, Igor Mammedov wrote:
>>> Describe how to enable and detect modern CPU hotplug interface.
>>> Detection part is based on new CPHP_GET_CPU_ID_CMD command,
>>> introduced by "acpi: cpuhp: add CPHP_GET_CPU_ID_CMD command" patch.
>>> Signed-off-by: Igor Mammedov <address@hidden>
>>> docs/specs/acpi_cpu_hotplug.txt | 22 ++++++++++++++++++++--
>>> 1 file changed, 20 insertions(+), 2 deletions(-)
>> Could we make this usecase / workflow independent of the new
>> CPHP_GET_CPU_ID_CMD command please?
>> I'd like to suggest the following:
>>> diff --git a/docs/specs/acpi_cpu_hotplug.txt
>>> index bb33144..667b264 100644
>>> --- a/docs/specs/acpi_cpu_hotplug.txt
>>> +++ b/docs/specs/acpi_cpu_hotplug.txt
>>> @@ -15,14 +15,14 @@ CPU present bitmap for:
>>> PIIX-PM (IO port 0xaf00-0xaf1f, 1-byte access)
>>> One bit per CPU. Bit position reflects corresponding CPU APIC ID.
>>> The first DWORD in bitmap is used in write mode to switch from legacy
>>> - to new CPU hotplug interface, write 0 into it to do switch.
>>> + to modern CPU hotplug interface, write 0 into it to do switch.
>>> QEMU sets corresponding CPU bit on hot-add event and issues SCI
>>> with GPE.2 event set. CPU present map is read by ACPI BIOS GPE.2 handler
>>> to notify OS about CPU hot-add events. CPU hot-remove isn't supported.
>>> -ACPI CPU hotplug interface registers:
>>> +Modern ACPI CPU hotplug interface registers:
>>> Register block base address:
>>> ICH9-LPC IO port 0x0cd8
>>> @@ -105,6 +105,24 @@ write access:
>>> other values: reserved
>>> Typical usecases:
>>> + - (x86) Detecting and enabling modern CPU hotplug interface.
>> (1) I think we can drop the (x86) restriction. (Because, we don't need
>> to depend on APIC ID specifics; see below.)
> I'd rather keep it x86 specific, as enabling interface and talking about
> legacy bitmap applies only to x86 impl.
> ARM one won't have any of it, it will just be enabled in a future QEMU
> (probably even without version-ed machine type).
> So could we just say usual "use firmware X.Y with QEMU Z to use CPU hotplug"
> in that case?
> Do we really need it to be arch agnostic?
No, I only suggested removing the x86 reference as a possible "extra"
improvement, from not depending on CPHP_GET_CPU_ID_CMD / APIC ID.