linux-kernel - [PATCH 4/4] clk: mediatek: mt8183: Add clk mux notifier for MFG mux

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Date:   Fri, 20 May 2022 17:43:23 +0800
From:   Chen-Yu Tsai <wenst@...omium.org>
To:     Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>
Cc:     Chen-Yu Tsai <wenst@...omium.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Chun-Jie Chen <chun-jie.chen@...iatek.com>,
        Miles Chen <miles.chen@...iatek.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        linux-clk@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH 4/4] clk: mediatek: mt8183: Add clk mux notifier for MFG mux

When the MFG PLL clock, which is upstream of the MFG clock, is changed,
the downstream clock and consumers need to be switched away from the PLL
over to a stable clock to avoid glitches.

This is done through the use of the newly added clk mux notifier. The
notifier is set on the mux itself instead of the upstream PLL, but in
practice this works, as the rate change notifitcations are propogated
throughout the sub-tree hanging off the PLL. Just before rate changes,
the MFG mux is temporarily and transparently switched to the 26 MHz
main crystal. After the rate change, the mux is switched back.

Signed-off-by: Chen-Yu Tsai <wenst@...omium.org>
---
 drivers/clk/mediatek/clk-mt8183.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/drivers/clk/mediatek/clk-mt8183.c b/drivers/clk/mediatek/clk-mt8183.c
index 8a755fadebb5..afef3738396e 100644
--- a/drivers/clk/mediatek/clk-mt8183.c
+++ b/drivers/clk/mediatek/clk-mt8183.c
@@ -1192,6 +1192,8 @@ static int clk_mt8183_top_probe(struct platform_device *pdev)
 {
 	void __iomem *base;
 	struct device_node *node = pdev->dev.of_node;
+	struct mtk_mux_nb *mfg_mux_nb;
+	int i, ret;
 
 	base = devm_platform_ioremap_resource(pdev, 0);
 	if (IS_ERR(base))
@@ -1217,6 +1219,25 @@ static int clk_mt8183_top_probe(struct platform_device *pdev)
 	mtk_clk_register_gates(node, top_clks, ARRAY_SIZE(top_clks),
 		top_clk_data);
 
+	/* Register mux notifier for MFG mux */
+	mfg_mux_nb = devm_kzalloc(&pdev->dev, sizeof(*mfg_mux_nb), GFP_KERNEL);
+	if (!mfg_mux_nb)
+		return -ENOMEM;
+
+	for (i = 0; i < ARRAY_SIZE(top_muxes); i++)
+		if (top_muxes[i].id == CLK_TOP_MUX_MFG)
+			break;
+	if (i == ARRAY_SIZE(top_muxes))
+		return -EINVAL;
+
+	mfg_mux_nb->mux = &top_muxes[i];
+	mfg_mux_nb->bypass_index = 0; // Bypass to 26M crystal
+	ret = devm_mtk_clk_mux_notifier_register(&pdev->dev,
+						 top_clk_data->hws[CLK_TOP_MUX_MFG]->clk,
+						 mfg_mux_nb);
+	if (ret)
+		return ret;
+
 	return of_clk_add_hw_provider(node, of_clk_hw_onecell_get,
 				      top_clk_data);
 }
-- 
2.36.1.124.g0e6072fb45-goog