Re: RFC about how to obtain PCIE TPH steer-tag on ARM64 platform

[Bjorn Helgaas <helgaas@kernel.org>]

On Fri, Jan 16, 2026 at 08:21:30AM +0800, fengchengwen wrote:
> On 1/15/2026 1:03 AM, Bjorn Helgaas wrote:
> > On Wed, Jan 14, 2026 at 11:39:27AM +0800, fengchengwen wrote:
> >> On 1/14/2026 3:07 AM, Bjorn Helgaas wrote:
> >>> On Mon, Jan 12, 2026 at 11:01:31AM +0800, fengchengwen wrote:
> >>>> Hi all,
> >>>>
> >>>> We want to enable PCIE TPH feature on ARM64 platform, but we encounter the
> >>>> following problem:
> >>>>
> >>>> 1. The pcie_tph_get_cpu_st() function invokes the ACPI DSM method to
> >>>>    obtain the steer-tag of the CPU. According to the definition of
> >>>>    the DSM method [1], the cpu_uid should be "ACPI processor uid".
> >>>
> >>>> 2. In the current implementation, the ACPI DSM method is invoked
> >>>>    directly using the logical core number, which works on the x86
> >>>>    platform but does not work on the ARM64 platform because the
> >>>>    logical core ID is not the same as the ACPI processor ID when the
> >>>>    PG exists.
> >>>
> >>> PG?
> >>
> >> partial good
> > 
> > I still don't know what "partial good" means :)  Is that something
> > from a spec?
> 
> Because of some issues (like manufacturing variances), certain circuits
> (e.g., some cores) might not work normally. For these cases, we can use
> the part at a reduced specification, which is the PG mentioned here.

Ah, got it :)  If you go this direction, maybe you can expand that
part of the commit log a bit, since I don't think "PG" or "partial
good" is a widely-known term.