Re: [PATCH 05/20] interconnect: qcom: icc-rpm: Introduce keep_alive

[Dmitry Baryshkov]

On 30/05/2023 13:20, Konrad Dybcio wrote:
> The downstream kernel employs the concept of "keeping the bus alive"
> by voting for the minimum (XO/19.2MHz) rate at all times on certain
> (well, most) buses.
> This is a very important thing to have, as if we
> either have a lackluster/wrong DT that doesn't specify a (high enough)
> vote on a certain bus, we may lose access to the entire bus altogether.
> This is very apparent when we only start introducing interconnect
> support on a given platform and haven't yet introduced voting on all
> peripherals.
>
> The same can happen if we only have a single driver casting a vote on
> a certain bus and that driver exits/crashes/suspends.
>
> The keepalive vote is limited to the ACTIVE bucket, as keeping a
> permanent vote on the SLEEP one could prevent the platform from properly
> entering low power mode states.
>
> Introduce the very same concept, with a slight twist: the vendor
> kernel checks whether the rate is zero before setting the minimum
> vote, but that's rather silly, as in doing so we're at the mercy
> of CCF. Instead, explicitly clamp the rates to always be >= 19.2 MHz
> for providers with keep_alive=true.
>
> Signed-off-by: Konrad Dybcio <konrad.dybcio@xxxxxxxxxx>
> ---
>   drivers/interconnect/qcom/icc-rpm.c | 10 ++++++++++
>   drivers/interconnect/qcom/icc-rpm.h |  3 +++
>   2 files changed, 13 insertions(+)

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>

--
With best wishes
Dmitry