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SubjectRe: [PATCH v4 2/2] ThunderX2: Add Cavium ThunderX2 SoC UNCORE PMU driver
On Sat, May 05, 2018 at 12:16:13AM +0530, Ganapatrao Kulkarni wrote:
> On Thu, Apr 26, 2018 at 4:29 PM, Mark Rutland <mark.rutland@arm.com> wrote:
> > On Wed, Apr 25, 2018 at 02:30:47PM +0530, Ganapatrao Kulkarni wrote:

> >> + *
> >> + * L3 Tile and DMC channel selection is through SMC call
> >> + * SMC call arguments,
> >> + * x0 = THUNDERX2_SMC_CALL_ID (Vendor SMC call Id)
> >> + * x1 = THUNDERX2_SMC_SET_CHANNEL (Id to set DMC/L3C channel)
> >> + * x2 = Node id
> >
> > How do we map Linux node IDs to the firmware's view of node IDs?
> >
> > I don't believe the two are necessarily the same -- Linux's node IDs are
> > a Linux-specific construct.
>
> both are same, it is numa node id from ACPI/firmware.

I am very wary about assuming that the Linux nid will always be the same
as the ACPI node id.

For that to *potentially* be true, this driver should depend on
CONFIG_NUMA, NUMA must not be disabled on the command line, etc, or the
node id will always be NUMA_NO_NODE.

I would be *much* happier if we had an explicit mapping somewhere to the
ID the FW expects.

> > It would be much nicer if we could pass something based on the MPIDR,
> > which is a known HW construct, or if this implicitly affected the
> > current node.
>
> IMO, node id is sufficient.

I agree that *a* node ID is sufficient, I just don't think that we're
guaranteed to have the specific node ID the FW wants.

> > It would be vastly more sane for this to not be muxed at all. :/
>
> i am helpless due to crappy hw design!

I'm certainly not blaming you for this! :)

I hope the HW designers don't make the same mistake in future, though...

Thanks,
Mark.

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