Re: [Qemu-devel] [PATCH v3 for-2.3 10/24] hw/apci: add _PRT method for extra PCI root busses

[Marcel Apfelbaum <marcel@redhat.com>]

On 03/08/2015 06:03 PM, Michael S. Tsirkin wrote:
> On Sun, Mar 08, 2015 at 05:37:25PM +0200, Marcel Apfelbaum wrote:
>> On 03/08/2015 05:27 PM, Michael S. Tsirkin wrote:
>>> On Sun, Mar 08, 2015 at 05:22:43PM +0200, Marcel Apfelbaum wrote:
>>>> On 03/08/2015 04:47 PM, Michael S. Tsirkin wrote:
>>>>> On Sun, Mar 08, 2015 at 01:04:07PM +0200, Marcel Apfelbaum wrote:
>>>>>> On 03/08/2015 12:46 PM, Michael S. Tsirkin wrote:
>>>>>>> On Thu, Mar 05, 2015 at 04:55:08PM +0200, Marcel Apfelbaum wrote:
>>>>>>>> Signed-off-by: Marcel Apfelbaum <marcel@redhat.com>
>>>>>>>
>>>>>>> some ideas for cleaning this up.
>>>>>>> there's more here btw.
>>>>>>>
>>>>>>>> ---
>>>>>>>>   hw/i386/acpi-build.c | 78 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>>>>>>>>   1 file changed, 78 insertions(+)
>>>>>>>>
>>>>>>>> diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
>>>>>>>> index e5709e8..f0401d2 100644
>>>>>>>> --- a/hw/i386/acpi-build.c
>>>>>>>> +++ b/hw/i386/acpi-build.c
>>>>>>>> @@ -664,6 +664,83 @@ static void build_append_pci_bus_devices(Aml *parent_scope, PCIBus *bus,
>>>>>>>>       aml_append(parent_scope, method);
>>>>>>>>   }
>>>>>>>>
>>>>>>>> +static Aml *build_prt(void)
>>>>>>>> +{
>>>>>>>> +    Aml *method, *pkg, *if_ctx, *while_ctx;
>>>>>>>> +
>>>>>>>> +    method = aml_method("_PRT", 0);
>>>>>>>> +
>>>>>>>> +    aml_append(method, aml_store(aml_package(128), aml_local(0)));
>>>>>>>> +    aml_append(method, aml_store(aml_int(0), aml_local(1)));
>>>>>>>> +    while_ctx = aml_while(aml_lless(aml_local(1), aml_int(128)));
>>>>>>>> +    {
>>>>>>>> +        aml_append(while_ctx,
>>>>>>>> +            aml_store(aml_shiftright(aml_local(1), aml_int(2)), aml_local(2)));
>>>>>>>> +        aml_append(while_ctx,
>>>>>>>> +            aml_store(aml_and(aml_add(aml_local(1), aml_local(2)), aml_int(3)),
>>>>>>>> +                      aml_local(3)));
>>>>>>>
>>>>>>>
>>>>>>> As an example, you can have
>>>>>>>
>>>>>>> Aml *i = aml_local(1);
>>>>>>> Aml *mask = aml_local(2);
>>>>>> Hi Michael,
>>>>>>
>>>>>> Thank you for the tip, the implementation is ready
>>>>>> and I'll submit it right away.
>>>>>
>>>>> So, one thing that's problematic here is that
>>>>> expected files need to be examined manually.
>>>> Only if pxb-device is added, otherwise they remain the same.
>>>> So by default, make check remains unchanged.
>>>>> How about a three-stage approach:
>>>>>
>>>>> 1. move _PRT out from DSDT - e.g. to a separate ssdt,
>>>>>     update expected files.
>>>>>     One way to do this is to first revert
>>>>> 	commit 4ec8d2b3f54dd1dcd9e2a80e529feff4e2603288
>>>>> 	Author: Igor Mammedov <imammedo@redhat.com>
>>>>> 	    pc: acpi-build: drop remaining ssdt_misc template
>>>>> 2. rewrite  the new SSDT in C,
>>>>>     produce an otherwise identical code.
>>>>>     make check will catch errors
>>>>> 3. reuse code from (2) for extra roots.
>>>>
>>>> I am aware of this and I was planning to do that on top of this series.
>>>> Four reasons for this:
>>>>   1. As stated before, it does not affect make check because this code
>>>>      affects the ACPI table only if pxb-device is present.
>>>>   2. The _PRT is not *exactly* the same, bus 0's _PRT has an extra "if" for
>>>>      the power-management device than needs needs SCI
>>>>   3. The series is already big, I prefer attacking this as a new enhancement:
>>>>      "Dynamically create bus 0 _PRT"
>>>>   4. QEMU 2.3 is approaching, I don't want o diverge now
>>>>
>>>>
>>>> Thanks,
>>>> Marcel
>>>
>>> Meanwhile 2.3 will have two almost identical copies of _PRT?
>>> I don't think that's a good idea.
>> The are 2 *different*  _PRTs for 2 different hw components.
>> The look the same only because I *preferred* them to look almost the same,
>> I could implement it differently.
>> There is actually nothing common about
>> 1. PIIX host bridge _PRT implemented statically
>> 2. pcb-device _PRT implemented in code.
>>
>> What is true is the series makes easier to implement dynamic _PRT
>> for any device, including PIIX host bridge. It doesn't mean we have two.
>>
>> Actually we need to think about using the same code, because changing it
>> would influence both devices.
>>
>> I really don't think they are related.
>> Thanks,
>> Marcel
>
>
> Come on, the same argument would make us duplicate almost
> any block of code. Copy-pasting always seems safer and faster
> than reusing, until you have to fix a bug in multiple places.
Completely agree, but this is not the case.
Here we have symmetric ways to solve this:
1. As I do: _PRT for PXB, then reuse it for piix host-bridge PXB code.
2. First the _PRT of piix host-bridge, then reuse it for PXB _PRT

And we still make the series longer and more complex.

Thanks,
Marcel

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