From: Laszlo Ersek <lersek@redhat.com>
To: Christophe de Dinechin <dinechin@redhat.com>, qemu-devel@nongnu.org
Cc: "Eduardo Habkost" <ehabkost@redhat.com>,
"Michael S. Tsirkin" <mst@redhat.com>,
"Gerd Hoffmann" <kraxel@redhat.com>,
"Igor Mammedov" <imammedo@redhat.com>,
"Paolo Bonzini" <pbonzini@redhat.com>,
"Philippe Mathieu-Daudé" <philmd@redhat.com>,
"Richard Henderson" <rth@twiddle.net>
Subject: Re: [RFC 1/3] acpi: cpuhp: fix 'Command data' description is spec
Date: Tue, 22 Oct 2019 19:37:05 +0200 [thread overview]
Message-ID: <c08fb6a1-aba4-4366-9366-a85369701060@redhat.com> (raw)
In-Reply-To: <m11rv4og2u.fsf@redhat.com>
(I've been dropped from the address list, not sure why)
On 10/22/19 19:17, Christophe de Dinechin wrote:
>
> Laszlo Ersek writes:
>
>> On 10/10/19 15:31, Laszlo Ersek wrote:
>>> 2nd round:
>>>
>>> On 10/09/19 15:22, Igor Mammedov wrote:
>>>> QEMU returns 0, in case of erro or invalid value in 'Command field',
>>>> make spec match reality, i.e.
>>>
>>> AHA! so this is exactly where you meant to list the particular cases
>>> when "command data" reads as 0:
>>> - CPU >= max_cpus selected,
>>> - CPU with pending events asked for, but none found
>>>
>>>> Also fix returned value description in case 'Command field' == 0x0,
>>>> it's in not PXM but CPU selector value with pending event
>>>>
>>>> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
>>>> ---
>>>> docs/specs/acpi_cpu_hotplug.txt | 5 +++--
>>>> 1 file changed, 3 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/docs/specs/acpi_cpu_hotplug.txt b/docs/specs/acpi_cpu_hotplug.txt
>>>> index ee219c8358..ac5903b2b1 100644
>>>> --- a/docs/specs/acpi_cpu_hotplug.txt
>>>> +++ b/docs/specs/acpi_cpu_hotplug.txt
>>>> @@ -44,9 +44,10 @@ read access:
>>>> 3-7: reserved and should be ignored by OSPM
>>>> [0x5-0x7] reserved
>>>> [0x8] Command data: (DWORD access)
>>>> - in case of error or unsupported command reads is 0xFFFFFFFF
>>>> + in case of error or unsupported command reads is 0x0
>>>> current 'Command field' value:
>>>> - 0: returns PXM value corresponding to device
>>>> + 0: returns CPU selector value corresponding to a CPU with
>>>> + pending event.
>>>>
>>>> write access:
>>>> offset:
>>>>
>>>
>>> How about:
>>>
>>> [0x8] Command data: (DWORD access, little endian)
>>> If the "CPU selector" value last stored by the guest refers to
>>> an impossible CPU, then 0.
>>> Otherwise, if the "Command field" value last stored by the
>>> guest differs from 0, then 0.
>>> Otherwise, if there is at least one CPU with a pending event,
>>> then that CPU has been selected; the command data register
>>> returns that selector.
>>> Otherwise, 0.
>>
>> Hmmm not exactly. Let me try again.
>>
>> [0x8] Command data: (DWORD access, little endian)
>> If the "CPU selector" value last stored by the guest refers to
>> an impossible CPU, then 0.
>> Otherwise, if the "Command field" value last stored by the
>> guest differs from 0, then 0.
>> Otherwise, the currently selected CPU.
>
> How about phrasing it to put the more general case first, e.g.
>
> [0x8] Command data: (DWORD access, little endian)
>
> The currently selected CPU, unless:
> - The "CPU selector" value refers to an impossible CPU
> - The "Command field" value last stored by the guest differs
> from 0
> In these last two cases, the value is 0.
I prefer my proposal because it translates to source code more directly
(a ladder of "if / else" pairs, or similar).
(I know that some programming languages support "unless"; I could never
wrap my brain around that idea! :) )
Thanks
Laszlo
next prev parent reply other threads:[~2019-10-22 17:38 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-09 13:22 [RFC 0/3] acpi: cphp: add CPHP_GET_CPU_ID_CMD command to cpu hotplug MMIO interface Igor Mammedov
2019-10-09 13:22 ` [RFC 1/3] acpi: cpuhp: fix 'Command data' description is spec Igor Mammedov
2019-10-10 12:33 ` Laszlo Ersek
2019-10-17 15:41 ` Igor Mammedov
2019-10-18 13:24 ` Laszlo Ersek
2019-10-10 13:31 ` Laszlo Ersek
2019-10-10 13:36 ` Laszlo Ersek
2019-10-22 17:17 ` Christophe de Dinechin
2019-10-22 17:37 ` Laszlo Ersek [this message]
2019-10-09 13:22 ` [RFC 2/3] acpi: cpuhp: add typical usecases into spec Igor Mammedov
2019-10-10 13:04 ` Laszlo Ersek
2019-10-10 13:15 ` Laszlo Ersek
2019-10-10 14:13 ` Laszlo Ersek
2019-10-18 14:45 ` Igor Mammedov
2019-10-09 13:22 ` [RFC 3/3] acpi: cpuhp: add CPHP_GET_CPU_ID_CMD command Igor Mammedov
2019-10-10 14:56 ` Laszlo Ersek
2019-10-10 15:06 ` Michael S. Tsirkin
2019-10-10 17:23 ` Igor Mammedov
2019-10-10 17:53 ` Laszlo Ersek
2019-10-10 19:26 ` Eduardo Habkost
2019-10-11 8:07 ` Laszlo Ersek
2019-10-18 16:18 ` Igor Mammedov
2019-10-21 13:06 ` Laszlo Ersek
2019-10-22 12:39 ` Laszlo Ersek
2019-10-22 14:42 ` Igor Mammedov
2019-10-22 15:49 ` Laszlo Ersek
2019-10-23 14:59 ` Igor Mammedov
2019-10-24 15:07 ` Philippe Mathieu-Daudé
2019-10-10 9:56 ` [RFC 0/3] acpi: cphp: add CPHP_GET_CPU_ID_CMD command to cpu hotplug MMIO interface Michael S. Tsirkin
2019-10-10 13:39 ` Igor Mammedov
2019-10-10 13:59 ` Michael S. Tsirkin
2019-10-10 15:57 ` Igor Mammedov
2019-10-10 18:15 ` Michael S. Tsirkin
2019-10-11 7:41 ` Laszlo Ersek
2019-10-10 19:20 ` Eduardo Habkost
2019-10-11 8:01 ` Laszlo Ersek
2019-10-11 13:00 ` Michael S. Tsirkin
2019-10-11 16:13 ` Laszlo Ersek
2019-10-11 10:47 ` Igor Mammedov
2019-10-11 6:54 ` Laszlo Ersek
2019-10-10 14:16 ` Eduardo Habkost
2019-10-10 14:49 ` Michael S. Tsirkin
2019-10-10 17:09 ` Igor Mammedov
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