Re: [PATCH] acpi/gpex: Inform os to keep firmware resource map

[Jiahui Cen <cenjiahui@huawei.com>]

Hi Michael,

On 2020/12/20 3:06, Michael S. Tsirkin wrote:
> On Fri, Dec 18, 2020 at 01:56:29PM +0800, Jiahui Cen wrote:
>> Hi Michael,
>>
>> On 2020/12/18 4:04, Michael S. Tsirkin wrote:
>>> On Thu, Dec 17, 2020 at 09:29:26PM +0800, Jiahui Cen wrote:
>>>> There may be some differences in pci resource assignment between guest os
>>>> and firmware.
>>>>
>>>> Eg. A Bridge with Bus [d2]
>>>>     -+-[0000:d2]---01.0-[d3]----01.0
>>>>
>>>>     where [d2:01.00] is a pcie-pci-bridge with BAR0 (mem, 64-bit, non-pref) [size=256]
>>>>           [d3:01.00] is a PCI Device with BAR0 (mem, 64-bit, pref) [size=128K]
>>>>                                           BAR4 (mem, 64-bit, pref) [size=64M]
>>>>
>>>>     In EDK2, the Resource Map would be:
>>>>         PciBus: Resource Map for Bridge [D2|01|00]
>>>>         Type = PMem64; Base = 0x8004000000;     Length = 0x4100000;     Alignment = 0x3FFFFFF
>>>>            Base = 0x8004000000; Length = 0x4000000;     Alignment = 0x3FFFFFF;  Owner = PCI [D3|01|00:20]
>>>>            Base = 0x8008000000; Length = 0x20000;       Alignment = 0x1FFFF;    Owner = PCI [D3|01|00:10]
>>>>         Type =  Mem64; Base = 0x8008100000;     Length = 0x100; Alignment = 0xFFF
>>>>
>>>>     While in Linux, kernel will use 0x2FFFFFF as the alignment to calculate
>>>>     the PMem64 size, which would be 0x6000000.
>>>>
>>>> The diffences could result in resource assignment failure.
>>>>
>>>> Using _DSM #5 method to inform guest os not to ignore the PCI configuration
>>>> that firmware has done at boot time could handle the differences.
>>>>
>>>> Signed-off-by: Jiahui Cen <cenjiahui@huawei.com>
>>>> ---
>>>>  hw/pci-host/gpex-acpi.c | 11 ++++++++++-
>>>>  1 file changed, 10 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/hw/pci-host/gpex-acpi.c b/hw/pci-host/gpex-acpi.c
>>>> index 071aa11b5c..2b490f3379 100644
>>>> --- a/hw/pci-host/gpex-acpi.c
>>>> +++ b/hw/pci-host/gpex-acpi.c
>>>> @@ -112,10 +112,19 @@ static void acpi_dsdt_add_pci_osc(Aml *dev)
>>>>      UUID = aml_touuid("E5C937D0-3553-4D7A-9117-EA4D19C3434D");
>>>>      ifctx = aml_if(aml_equal(aml_arg(0), UUID));
>>>>      ifctx1 = aml_if(aml_equal(aml_arg(2), aml_int(0)));
>>>> -    uint8_t byte_list[1] = {1};
>>>> +    uint8_t byte_list[1] = {0x21};
>>>>      buf = aml_buffer(1, byte_list);
>>>
>>>
>>> Hmm what is this change for?
>>>
>>> I also noticed something weird.
>>> Spec seems to say for _DSM for PCI Express Slot Information:
>>>
>>>
>>> Arguments:
>>> Arg0: UUID: E5C937D0-3553-4d7a-9117-EA4D19C3434D
>>> Arg1: Revision ID: 2
>>> Arg2: Function Index: 1
>>> Arg3: Empty Package
>>>
>>>
>>> how come we are comparing function index to 0 here?
>>>
>>
>> PCI Firmware Spec says in 4.6.1. _DSM for PCI Express Slot Information
>>
>> Note: Function 0 is a generic Query function that is supported by _DSMs with any UUID and
>> Revision ID. The definition of function 0 is generic to _DSM and specified in the ACPI Specification,
>> Version 3.0 (or later).
>>
>>
>> And ACPI Spec says in 9.1.1 _DSM (Device Specific Method)
>>
>> Return Value Information:
>> If Function Index is zero, the return is a buffer containing one bit for each function index, starting with zero. Bit 0
>> indicates whether there is support for any functions other than function 0 for the specified UUID and Revision ID.
>> If set to zero, no functions are supported (other than function zero) for the specified UUID and Revision ID. If set
>> to one, at least one additional function is supported. For all other bits in the buffer, a bit is set to zero to indicate if
>> that function index is not supported for the specific UUID and Revision ID. (For example, bit 1 set to 0 indicates that
>> function index 1 is not supported for the specific UUID and Revision ID.)
>>
>>
>> I have no idea whether the original code does aim to use _DSM #0
>> by setting function index 0 (The return value seems not to be suitable
>> with _DSM #1). But if it does, I think it is necessary to set bit 5
>> in return value to indicate _DSM #5 function is supported.
> 
> 
> 
> So let's make it self documenting:
> 
> {
> 	0x1 << 0 /* support for support for any functions other than function 0 */ |
> 	0x1 << 5 /* support for function 5 */
> }
> 
> 
> 
>>>
>>> Also, as long as we are changing this probably shouldn't hard-code
>>> 1 as array size ...
>>>
>>
>> Is a macro enough? Like #define RET_BUF_SIZE 2
> 
> Better to use 
> 
> uint8_t byte_list[] = { ... };
> 
> And then ARRAY_SIZE(byte_list)
> 

Got it. I'll fix in the next patch.

Thanks,
Jiahui

> 
>>>
>>>>      aml_append(ifctx1, aml_return(buf));
>>>>      aml_append(ifctx, ifctx1);
>>>> +
>>>> +    /* PCI Firmware Specification 3.2
>>>> +     * 4.6.5. _DSM for Ignoring PCI Boot Configurations
>>>
>>> Note you must always quote the most recent spec that
>>> your change refers to. This is so people can figure out
>>> legacy guest compatibility.
>>>
>>> In this case I think this first appeard in 3.1 not 3.2
>>>
>>
>> OK, I'll fix this.
>>
>>>> +     * The UUID in _DSM in this context is
>>>> +     * {E5C937D0-3553-4D7A-9117-EA4D19C3434D}
>>>
>>> This is just five lines earier, I don't think we need it here.
>>>
>>
>> Will remove.
>>
>>>> +     */
>>>> +    ifctx1 = aml_if(aml_equal(aml_arg(2), aml_int(5)));
>>>
>>> add comment:
>>> 	/* Arg2: Function Index: 5 */
>>
>> Will add.
>>
>>>
>>>> +    aml_append(ifctx1, aml_return(aml_int(0)));
>>>
>>>
>>> add comment: /* 0 - do not ignore ... (quote spec I don't have it to hand) */
>>>
>>
>> Will add.
>>
>> Thanks,
>> Jiahui
>>
>>>
>>>
>>>
>>>> +    aml_append(ifctx, ifctx1);
>>>>      aml_append(method, ifctx);
>>>>  
>>>>      byte_list[0] = 0;
>>>> -- 
>>>> 2.28.0
>>>
>>> .
>>>
> 
> .
>