linux-kernel - Re: [PATCH] clk: qcom: gcc-sm8450: set OPS_PARENT_ENABLE on gcc_sdcc2_apps_clk

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Date: Mon, 29 Apr 2024 17:21:05 -0700
From: Stephen Boyd <sboyd@...nel.org>
To: Bjorn Andersson <andersson@...nel.org>, Konrad Dybcio <konrad.dybcio@...aro.org>, Michael Turquette <mturquette@...libre.com>, Vinod Koul <vkoul@...nel.org>
Cc: Marijn Suijten <marijn.suijten@...ainline.org>, linux-arm-msm@...r.kernel.org, linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org, Dmitry Baryshkov <dmitry.baryshkov@...aro.org>, Konrad Dybcio <konrad.dybcio@...aro.org>
Subject: Re: [PATCH] clk: qcom: gcc-sm8450: set OPS_PARENT_ENABLE on gcc_sdcc2_apps_clk_src

Quoting Konrad Dybcio (2024-04-27 05:01:07)
> Similar to how it works on other SoCs, the top frequency of the SDHCI2
> core clock is generated by a separate PLL (peculiar design choice) that
> is not guaranteed to be enabled (why does the clock framework not handle
> this by default?).
> 
> Add the CLK_OPS_PARENT_ENABLE flag to make sure we're not muxing the
> RCG input to a dormant source.

The RCG2 hardware hasn't required the parent to be enabled for clk
operations besides for the glitch-free source switch. What scenario is
happening here that's requiring this flag? Is the RCG forcibly enabled
perhaps because the bootloader has left the root enable bit set
(CMD_ROOT_EN)? Or are we changing the parent while the clk framework
thinks the clk is off when it is actually on?

TL;DR: This is papering over a bigger bug.