Re: [PATCH v2 00/13] SCMI Clock rates discovery rework

Hi Cristian,

On Tue, 10 Mar 2026 at 19:40, Cristian Marussi [off-list ref] wrote:

it was a known limitation, in the SCMI Clock protocol support, the lack of
dynamic allocation around per-clock rates discovery: fixed size statically
per-clock rates arrays did not scale and was increasingly a waste of memory
(see [1]).

This series aim at solving this in successive steps:

 - simplify and reduce to the minimum possible the rates data info exposed
   to the SCMI driver by scmi_clock_info
 - move away from static fixed allocation of per-clock rates arrays in
   favour of a completely dynamic runtime allocation: just allocate what
   is needed based on the effectively discovered

This is done in patches 2-6.

A further bigger optimization suggested in a past series [2] by Etienne
would be, whenever allowed by the spec, to limit upfront the number of
queries in order to simply retrieve min and max rate, that are indeed the
only rates needed by the CLK SCMI driver.

The approach proposed in [1] was open coding and duplicating some of the
functionalities already provided by SCMI iterators, though.

Patch 7-12 implement such optimization instead by:

 - reworking core SCMI iterators to support bound enumerations
 - use such new bound iterators to perform the minimum number of queries
   in order to only retrieve min an max rate

As a final result now the rates enumeration triggered by the CLK SCMI
driver, while still allocating for all the existent rates, miminize the
number of SCMI CLK_DESCRIBE_RATE messages needed to obtain min and max.

Finally, patch 13 introduces a new clock protocol operation to be able to
trigger anytime on demand a full enumeration and obtain the full list of
rates when needed, not only min/max: this latter method is really only used
currently by some dowstream SCMI Test driver of mine.

Based on v7.0-rc3.
Tested on JUNO and an emulated environment.

Beside addressing a few review comments, in V2:

 - patch [1/13] introduces a fix for the pre-existing rounding algorithm,
   before relocating the algorithm logic as alreday done in V1.
 - patch [8/13] hardens clock protocol initialization by adding some
   missing retval checks

Thank you, this removes the need for increasing SCMI_MAX_NUM_RATES on
R-Car X5H, while decreasing memory usage.

As upstream does not support SCMI on R-Car X5H yet, I am ignoring
the hardening for now (it may be fixed by a quirk), so
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds