>>> on new requests. This function gets called quite a lot and I'm trying not to
>>> make it too heavy weight.
>>
>> Generally, nothing should be accessing the same DT value frequently.
>> It should get cached somewhere.
>>
>
> The problem appears for DTs that don't have the pci-domain info. Then the cached
> value is left at the default non-valid value and attempts to rescan the DT will
> be made every time the function is called.
>
>> I don't really understand how domains are used so it's hard to provide
>> a recommendation here. Do domains even belong in the DT?
>
> ACPI calls them segments and the way Bjorn explained it to me at some moment was
> that it was an attempt to split up a bus in different groups (or alternatively,
> merge a few busses together). To be honest I haven't seen systems where the domain
> is anything other than zero, but JasonG (or maybe Benjamin) were floating an
> idea of using the domain number to identify physical slots.
PCI domain(or named segment) is provided by firmware, in ACPI system, we evaluated it
by method "_SEG". in IA64 with ACPI, PCI hostbridge driver retrieves the domain from ACPI,
if it's absent, the default domain is zero. So I wonder why in DTS, if it's absent, we get
a auto increment domain value.
PCI get domain by ACPI "_SEG" in IA64(drivers/acpi/pci_root.c)
......
status = acpi_evaluate_integer(handle, METHOD_NAME__SEG, NULL,
&segment);
if (ACPI_FAILURE(status) && status != AE_NOT_FOUND) {
dev_err(&device->dev, "can't evaluate _SEG\n");
result = -ENODEV;
goto end;
}
.......
Thanks!
Yijing.
>
>> This function
>> is just a weird mixture of data retrieval and allocation. I think you
>> need to separate it into 2 functions.
>
> It is meant to do allocation with the retrieval being a short-cut (or fine
> control if you want).
>
> I need to think a bit more for a better solution.
>
> Best regards,
> Liviu
>
>>
>> Rob
>>
>
--
Thanks!
Yijing
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