Re: [PATCH v2 09/15] scsi: ufs: deprecate 'freq-table-hz' property

On Wed 23 Feb 03:15 CST 2022, Krzysztof Kozlowski wrote:

On 22/02/2022 19:16, Bjorn Andersson wrote:

quoted

On Tue 22 Feb 06:58 PST 2022, Krzysztof Kozlowski wrote:

quoted

The 'freq-table-hz' is not correct in DT schema, because '-hz' suffix
defines uint32 type, not an array.  Therefore deprecate 'freq-table-hz'
and use 'freq-table' instead.

Patch looks good in itself, but why don't we use opp-table to describe
the performance states?

In particular looking at the two columns of frequencies for various
Qualcomm boards they require different performance-states.

A concrete example is sm8350.dtsi, which specifies 75MHz and 300MHz as
the first frequency pair. The lower level requires the VDD_CX power rail
to be at least &rpmhpd_opp_low_svs, the higher frequency has a
required-opps of &rpmhpd_opp_nom.


As this isn't possible to express in the current binding we've just been
forced to always run at a higher voltage level and kept this in the todo
list.

But rather than migrating freq-table-hz to freq-table and then having to
introduce an opp table to express the power constraints, could we
perhaps skip the intermediate step?

Or would you have any other suggestion about how we can represent the
required-opps level together with the freq-table (if that's what we want
to stick with).

Usage of OPP tables is interesting solution. It would solve your problem
of power rail levels. This would need several opp-tables - one for each
clock, which is not a big problem.

Ahh, so we can only have a single clock, but multiple regulators and
interconnect paths tied to the opp table.

We have a couple of cases where it would have been nice to be able to
key the opp-table off some index (e.g. the UFS gear or PCI Gen) and
control multiple clocks. So I think we need to look into this further...

The problem is that I do not have any UFS hardware (none of my Samsung
Exynos boards have UFS... I don't have even arm64 Exynos chips :( ), so
implementing it theoretically will be painful.
OTOH, I believe that having a working dtschema is very useful. Having
dtschema without errors/warnings is even worth some churn/intermediary work.

The intermediary work is also not that big. Once proper OPP is
implemented, we will have "just" two deprecated properties in the bindings.

Fair enough, was just hoping to avoid the middle step. But that's fine,
we'll continue to carry this on our todo list then.

Thanks,
Bjorn

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