linux-kernel - [PATCH v2] clk: qcom: clk-alpha-pll: Don't reconfigure running Trion

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Date:   Tue, 23 Nov 2021 08:25:08 -0800
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Taniya Das <tdas@...eaurora.org>, Vinod Koul <vkoul@...nel.org>
Cc:     Robert Foss <robert.foss@...aro.org>,
        linux-arm-msm@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2] clk: qcom: clk-alpha-pll: Don't reconfigure running Trion

In the event that the bootloader has configured the Trion PLL as source
for the display clocks, e.g. for the continuous splashscreen, then there
will also be RCGs that are clocked by this instance.

Reconfiguring, and in particular disabling the output of, the PLL will
cause issues for these downstream RCGs and has been shown to prevent
them from being re-parented.

Follow downstream and skip configuration if it's determined that the PLL
is already running.

Fixes: 59128c20a6a9 ("clk: qcom: clk-alpha-pll: Add support for controlling Lucid PLLs")
Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
---

Changes since v1:
- Forgot to commit the last minute s/pr_dbg/pr_debug/

 drivers/clk/qcom/clk-alpha-pll.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/clk/qcom/clk-alpha-pll.c b/drivers/clk/qcom/clk-alpha-pll.c
index eaedcceb766f..8f65b9bdafce 100644
--- a/drivers/clk/qcom/clk-alpha-pll.c
+++ b/drivers/clk/qcom/clk-alpha-pll.c
@@ -1429,6 +1429,15 @@ EXPORT_SYMBOL_GPL(clk_alpha_pll_postdiv_fabia_ops);
 void clk_trion_pll_configure(struct clk_alpha_pll *pll, struct regmap *regmap,
 			     const struct alpha_pll_config *config)
 {
+	/*
+	 * If the bootloader left the PLL enabled it's likely that there are
+	 * RCGs that will lock up if we disable the PLL below.
+	 */
+	if (trion_pll_is_enabled(pll, regmap)) {
+		pr_debug("Trion PLL is already enabled, skipping configuration\n");
+		return;
+	}
+
 	clk_alpha_pll_write_config(regmap, PLL_L_VAL(pll), config->l);
 	regmap_write(regmap, PLL_CAL_L_VAL(pll), TRION_PLL_CAL_VAL);
 	clk_alpha_pll_write_config(regmap, PLL_ALPHA_VAL(pll), config->alpha);
-- 
2.33.1