On 2/24/20 9:21 PM, Borislav Petkov wrote:
> On Thu, Jan 23, 2020 at 09:41:43AM +0800, Cao jin wrote:
>> Current processing logic is confusing.
>>
>> Return value of early_acpi_parse_madt_lapic_addr_ovr() indicates error(< 0),
>> parsed entry number(>= 0).
>
> You mean, the count of table entries parsed successfully?
Yes, 0 for no override sub-table.
>
>> So, it makes no sense to initialize acpi_lapic & smp_found_config
>> seeing no override entry, instead, initialize them seeing MADT.
>
> Err, that logical conclusion is not really clear to me - pls try
> again with more detail. I kinda see what you mean by looking at
> acpi_process_madt() but before I commit a change like that, I better
> have the warm and fuzzy feeling that it is correct and properly
> explained in its commit message.
>
My understanding of early_acpi_process_madt(): mainly for getting APIC
register base address(acpi_lapic_addr) from MADT, then process it via
register_lapic_address(). acpi_lapic_addr could be got from one of
following 2 places:
1. MADT header (32-bit address, always exist)
2. MADT sub-table: Local APIC Address Override (64-bit address,
optional, high priority and use it if present)
So the making-sense logic to me goes like:
1. get (32-bit) acpi_lapic_addr from MADT header.
2. check if there is MADT override structure & get 64-bit
acpi_lapic_addr if present.
3. register_lapic_address(acpi_lapic_addr);
Then, it looks weird to me putting register_lapic_address() into
early_acpi_parse_madt_lapic_addr_ovr(), the result is not wrong, but the
code logic is hard for newbie. (these 2 functions both does more than
its name tells, register_lapic_address() also get boot cpu APIC ID &
version.)
Variable acpi_lapic and its counterpart smp_found_config from MPS
indicate whether it is SMP system, right? The following code:
error = early_acpi_parse_madt_lapic_addr_ovr();
if (!error) {
acpi_lapic = 1;
smp_found_config = 1;
}
means setting them when there is no override sub-table, so why can't
moving the setting operation out? Another issue: if there *is* override
sub-table, don't set those two?
> So why did
>
> cbf9bd603ab1 ("acpi: get boot_cpu_id as early for k8_scan_nodes")
>
> do it this way? Was it wrong or why?
Not a clue... The title says it wants boot_cpu_physical_apicid, but did
many other things. Maybe Thomas could provide some insights?
>
> I'm very wary about touching ACPI parsing code for no good reason
> because, well, it is ACPI...
I was expecting ACPI guys could help to confirm;) I also understand this
should be tested widely, but I just have a normal PC, so it is a RFC:)
--
Sincerely,
Cao jin
