Re: [PATCH v2 1/2] ACPI/PPTT: Add support for ACPI 6.3 thread flag

From: John Garry
Date: Wed Jun 19 2019 - 05:20:42 EST

On 18/06/2019 22:28, Jeremy Linton wrote:

On 6/18/19 12:23 PM, John Garry wrote:
On 18/06/2019 15:40, Valentin Schneider wrote:
On 18/06/2019 15:21, Jeremy Linton wrote:
+ * Return: -ENOENT if the PPTT doesn't exist, the CPU cannot be
found or
+ * the table revision isn't new enough.
+ * Otherwise returns flag value
+ */

Nit: strictly speaking we're not returning the flag value but its mask
applied to the flags field. I don't think anyone will care about
the actual flag value, but it should be made obvious in the doc:

Or I clarify the code to actually do what the comments says. Maybe
that is what John G was also pointing out too?

No, I was just saying that the kernel topology can be broken without
this series.

Mmm I didn't find any reply from John regarding this in v1, but I
mind either way, as long as the doc & code are aligned.

BTW, to me, function acpi_pptt_cpu_is_thread() seems to try to do too
much, i.e. check if the PPTT is new enough to support the thread flag
and also check if it is set for a specific cpu. I'd consider separate
functions here.


? Your suggesting replacing the

I am not saying definitely that this should be changed, it's just that acpi_pptt_cpu_is_thread() returning false, true, or "no entry" is not a typical API format.

How about acpi_pptt_support_thread_info(cpu) and acpi_pptt_cpu_is_threaded(cpu), both returning false/true only?

None of this is ideal.

BTW, Have you audited which arm64 systems have MT bit set legitimately?

if (table->revision >= rev)

I know that checking the table revision is not on the fast path, but it seems unnecessarily inefficient to always read it this way, I mean calling acpi_table_get().

Can you have a static value for the table revision? Or is this just how other table info is accessed in ACPI code?

cpu_node = acpi_find_processor_node(table, acpi_cpu_id);

check with

if (revision_check(table, rev))
cpu_node = acpi_find_processor_node(table, acpi_cpu_id);

and a function like

static int revision_check(acpixxxx *table, int rev)
return (table->revision >= rev);

Although, frankly if one were to do this, it should probably be a macro
with the table type, and used in the dozen or so other places I found
doing similar checks (spcr, iort, etc).

Or something else?