linux-kernel - Re: [PATCH v4 7/7] clk: qcom: add the driver for the MSM8996 APCS clocks

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Message-ID: <6db0c9da3a05ee8adaf7262ebce16d3d.sboyd@kernel.org>
Date:   Wed, 25 Jan 2023 15:15:40 -0800
From:   Stephen Boyd <sboyd@...nel.org>
To:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Jassi Brar <jassisinghbrar@...il.com>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Michael Turquette <mturquette@...libre.com>,
        Rob Herring <robh+dt@...nel.org>,
        Taniya Das <quic_tdas@...cinc.com>
Cc:     linux-arm-msm@...r.kernel.org, linux-clk@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 7/7] clk: qcom: add the driver for the MSM8996 APCS clocks

Quoting Konrad Dybcio (2023-01-25 14:05:27)
> 
> On 25.01.2023 22:56, Stephen Boyd wrote:
> > 
> > So it is waiting for the CPU clk to be stable? The comment is not clear.
> Okay, so perhaps this is just a misunderstanding because of a lackluster
> comment.. This SYS_APCS_AUX (provided by this driver) is one of the CPU
> clock sources (and probably the "safest" of them all, as it's fed by
> GPLL0 and not the CPU PLLs) the delay is there to ensure it can
> stabilize after setting the divider to DIV2. In a theoretical case, the
> big 8996 cpucc driver could select this clock as a target for one (or
> both) of the per-cluster muxes and it could put the CPUs in a weird state.
> 
> As unlikely as that would be, especially considering 8996 (AFAIK) doesn't
> use this clock source coming out of reset / bootloader, this lets us
> ensure one less thing can break.

Great! I look forward to a better comment.