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

[Ard Biesheuvel]

On 12/17/20 6:23 PM, Laszlo Ersek wrote:
> On 12/17/20 14:52, Jiahui Cen wrote:
>> +Laszlo
>>
>> On 2020/12/17 21:29, 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);
>>>      aml_append(ifctx1, aml_return(buf));
>>>      aml_append(ifctx, ifctx1);
>>> +
>>> +    /* PCI Firmware Specification 3.2
>>> +     * 4.6.5. _DSM for Ignoring PCI Boot Configurations
>>> +     * The UUID in _DSM in this context is
>>> +     * {E5C937D0-3553-4D7A-9117-EA4D19C3434D}
>>> +     */
>>> +    ifctx1 = aml_if(aml_equal(aml_arg(2), aml_int(5)));
>>> +    aml_append(ifctx1, aml_return(aml_int(0)));
>>> +    aml_append(ifctx, ifctx1);
>>>      aml_append(method, ifctx);
>>>  
>>>      byte_list[0] = 0;
>>>
>>
> 
> Seems to make sense to me (I didn't realize we already had the _DSM
> method with this GUID!), but now I'm not sure what to expect of the
> guest kernel, in light of what Ard said. So if it works now, is that by
> accident, or is it an intentional, fresh commit in the kernel? Like
> a78cf9657ba5 ("PCI/ACPI: Evaluate PCI Boot Configuration _DSM", 2019-06-21)?
> 
> Benjamin: can you please tell us something about this Linux commit? What
> was the motivation for it?
> 
> Hmm.... this commit seems to be a part of the following series:
> 
> a78cf9657ba5 PCI/ACPI: Evaluate PCI Boot Configuration _DSM
> 7ac0d094fbe9 PCI: Don't auto-realloc if we're preserving firmware config
> 3e8ba9686600 arm64: PCI: Allow resource reallocation if necessary
> 85dc04136e86 arm64: PCI: Preserve firmware configuration when desired
> 
> OK, after reading through the commit messages in those commits (esp.
> 7ac0d094fbe9), I think the Linux change was made exactly for the purpose
> that we want it for -- stick with the firmware assignments.
> 
> Ard, does that seem right, or am I misunderstanding the kernel series?
> 

Hmm, I had no recollection of those changes going in, but I was clearly
aware at the time, given my acks.

So we clearly do support DSM #5 to prevent resource reallocation, and it
makes sense to use it in the proposed way.