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

[John Garry]

On 18/06/2019 22:28, Jeremy Linton wrote:
> Hi,
>
> 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
> > > > > getting
> > > > > 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
> > > wouldn't
> > > 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.

Hi,

> ? 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?

thanks,
John

> > > [...]
> > >
> > > .
>
>
> .