Re: [PATCH v15 10/35] firmware: arm_scmi: Add Telemetry resources enumeration

[Jonathan Cameron <jonathan.cameron@oss.qualcomm.com>]

On Mon,  9 Nov 2026 09:11:56 +0000
Cristian Marussi <cristian.marussi@arm.com> wrote:

> Add basic Telemetry allocation and initialization routines, introducing and
> wiring-up the logic needed to enumerate all the SCMI Telemetry resources
> optionally using a lazy on-demand scheme: this approach factors in the
> flexibility needed to minimize the amount of initialization work based on
> the effective access pattern used by the upper layer ABI.
> 
> Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>

Hi Cristian,

This stretches across the patch set but first elements related to it are
in this patch.  How do we handle larger values of de_data_sz?

The spec allows (and it's useful for things like histograms)
DEs to have an integer multiple of 64 bits for a single element.
In the shared memory buffer that just ends up with a bunch of matching
IDs with discovery via the parsing done in this patch.

The only (I think) today to dump that from this patch set is
to use the shmti dump interface.  That's not exactly nice!

I messed around with (well chatted with an LLM about) a couple of
options.

1. Make the whole stack aware of multi line DEs. So all the requests
   get to return more data.
2. Adding indexing so you can get a multi line DE in multiple calls.
   That makes the interface for a bulk read a bit odd.  Userspace will
   have to be cleverer given variable sized elements.

Given this is a ABI related aspect, needs figuring out sooner rather
than later I think.

Which way do you think makes more sense?  Or am I missing something?

Jonathan