Re: [PATCH v2 0/9] soc: qcom: geni: Derive SE clock configuration from OPP table on SA8255P

[Ulf Hansson]

On Tue, Sep 1, 2026 at 6:48 PM Praveen Talari
<praveen.talari@xxxxxxxxxxxxxxxx> wrote:
>
> Hi Ulf,
>
> On 01-09-2026 20:22, Ulf Hansson wrote:
> > On Thu, Aug 27, 2026 at 7:59 PM Praveen Talari
> > <praveen.talari@xxxxxxxxxxxxxxxx> wrote:
> >> On firmware-managed platforms such as SA8255P, there is no Linux clock
> >> handler available to determine the appropriate SE source clock, source
> >> clock index, and divider values for a requested protocol frequency.
> >> However, these parameters are required when programming GSI TREs, where
> >> the hardware expects an explicit clock source selection and divider
> >> configuration for the serial engine.
> >>
> >> In contrast, platforms using Linux-managed clocks derive these
> >> parameters through geni_se_clk_freq_match() using the source clock
> >> information stored in clk_perf_tbl. Since the firmware-managed path
> >> lacks equivalent clock information, protocol drivers cannot reuse the
> >> existing frequency matching logic and instead rely on a direct mapping
> >> between protocol-requested frequencies and performance levels. This
> >> creates a separate clock configuration flow and prevents
> >> firmware-managed platforms from deriving the actual SE clock parameters
> >> required for GSI TRE programming.
> > Hmm, this sounds like moving backwards when it comes to keeping
> > drivers as portable as possible.
> >
> > I understand geni_se_clk_freq_match() has been around for a while, but
> > fortunately its use seems limited to only a few qcom specific drivers.
> >
> > Rather than continue down this path, would it not be possible to find
> > a more generic solution for "geni_se_clk_freq_match()"? Can we replace
> > it with a common clock/OPP API? In this way, we would not need to
> > sprinkle drivers with calls to platform specific  code.
> I agree that protocol drivers should not need to know whether GENI resources
> are managed through the clock framework or a firmware-provided
> performance domain.
>
> The intent of this series is actually to move in that direction rather than
> introduce a separate flow. Today firmware-managed platforms cannot use
> geni_se_clk_freq_match() because clk_perf_tbl is only populated when a
> Linux clock
> is present. This series derives the same clock-performance
> information(clk_perf_tbl) from the OPP
> table and populates clk_perf_tbl during geni_se_domain_attach(),
> allowing both
> resource-management models to reuse the existing
> geni_se_clk_freq_match() infrastructure.

Right, the goal makes sense, but I am not sure the proposed solution
is the way to get there.

We really want to avoid having generic drivers like (spi, uart, i2c,
etc) calling platform specific functions. This isn't just me, it's the
general way for how we do things for drivers. Of course, we have
exceptions, but I think you get my point.

In this case, why isn't it possible to use the clock and OPP
framework? Is there anything missing to make this work?

>
> Likewise, geni_se_set_rate() hides whether the underlying implementation
> uses
> dev_pm_opp_set_rate() on a perf-domain device or a regular clock-backed
> device,
> so protocol drivers no longer need platform-specific callbacks. The goal
> is to
> converge both paths behind common GENI helpers rather than maintain separate
> clock-selection mechanisms.

The OPP layer already has some capabilities for managing clocks. Can't
we use devm_pm_opp_set_config() to prepare an OPP table with the
relevant clk data for the devices, as a way to abstract things?

> >
> >> To address this limitation, the performance-domain OPP table is treated
> >> as the representation of SE-supported source clock frequencies. During
> >> geni_se_domain_attach(), the OPP entries are used to populate
> >> clk_perf_tbl and related clock performance data, allowing
> >> firmware-managed platforms to leverage the same clock frequency matching
> >> infrastructure used by Linux-managed platforms.
> >>
> >> With this change, protocol drivers can use geni_se_clk_freq_match() to
> >> select the closest supported source clock frequency for a requested
> >> protocol rate, derive the corresponding source clock index and divider
> >> values required for GSI TRE programming, and apply the matched clock
> >> through the OPP framework. This removes the dependency on direct
> >> protocol-frequency-to-performance-level mappings and provides a common
> >> clock selection and configuration mechanism across both firmware-managed
> >> and Linux-managed GENI deployments.
> > Rather than adding yet another platform specific method, would it be
> > possible to extend the generic OPP library with the pieces that are
> > missing to make this work in a generic way?
> I agree with the goal of using generic infrastructure. However,
> geni_se_clk_freq_match()
> derives GENI-specific parameters such as the source clock, clock index,
> and divider values
> required for GSI TRE programming, which are not represented by the
> generic OPP interface today.
>
> This series does not introduce a new clock selection path; it reuses the
> existing
> geni_se_clk_freq_match() flow on firmware-managed platforms by populating
> clk_perf_tbl from OPP data.

So geni_se_clk_freq_match() is used by two consumer drivers today,
drivers/spi/spi-geni-qcom.c and drivers/tty/serial/qcom_geni_serial.c.

Beyond the $subject series, there will be even more consumer drivers
that call these platform specific functions. As I said above, I don't
think this is moving things in the right direction.

If this can't be solved with generic frameworks (clocks and OPP),
please clarify why so we can figure out a better way forward.

[...]

Kind regards
Uffe