Re: [PATCH] clk: qcom: gcc-sm8450: set OPS_PARENT_ENABLE on gcc_sdcc2_apps_clk_src

From: Stephen Boyd <sboyd@kernel.org>
To: Bjorn Andersson <andersson@kernel.org>,
	Konrad Dybcio <konrad.dybcio@linaro.org>,
	Michael Turquette <mturquette@baylibre.com>,
	Vinod Koul <vkoul@kernel.org>
Cc: Marijn Suijten <marijn.suijten@somainline.org>,
	linux-arm-msm@vger.kernel.org, linux-clk@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	Dmitry Baryshkov <dmitry.baryshkov@linaro.org>,
	Konrad Dybcio <konrad.dybcio@linaro.org>
Subject: Re: [PATCH] clk: qcom: gcc-sm8450: set OPS_PARENT_ENABLE on gcc_sdcc2_apps_clk_src
Date: Mon, 29 Apr 2024 17:21:05 -0700	[thread overview]
Message-ID: <2337ba58adb3fb127710bead9b8665a9.sboyd@kernel.org> (raw)
In-Reply-To: <20240427-topic-8450sdc2-v1-1-631cbb59e0e5@linaro.org>

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.