linux-kernel - Re: [PATCH 05/20] interconnect: qcom: icc-rpm: Introduce keep

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Date:   Thu, 1 Jun 2023 12:54:03 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Georgi Djakov <djakov@...nel.org>,
        Leo Yan <leo.yan@...aro.org>, Evan Green <evgreen@...omium.org>
Cc:     Marijn Suijten <marijn.suijten@...ainline.org>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-clk@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH 05/20] interconnect: qcom: icc-rpm: Introduce keep_alive

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@...aro.org>
> ---
>   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@...aro.org>

-- 
With best wishes
Dmitry