[PATCH v1 3/4] clk: sunxi-ng: sun55i-a523: reparent GPU while pll-gpu changes rate

[Juan Manuel López Carrillo]

Register the existing sunxi-ng mux notifier on pll-gpu so the GPU mod
clock is parked on the fixed pll-periph0-600M output while the PLL is
being reprogrammed, and switched back once it has locked, following the
cpux precedent of other sunxi SoCs.  The mux switch is glitch-free per
the T527 manual (GPU_CLK_REG, "The clock selection supports glitch-free
switch").

Nothing retunes pll-gpu at runtime today (the mux does not propagate
rate requests and all standard OPPs resolve to pll-periph0 outputs),
but the higher speed-bin operating points (648-792 MHz) will need
pll-gpu as a live parent, and any direct clk_set_rate() on the PLL is
now safe.

Signed-off-by: Juan Manuel López Carrillo <juanmanuellopezcarrillo@xxxxxxxxx>
---
 drivers/clk/sunxi-ng/ccu-sun55i-a523.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/clk/sunxi-ng/ccu-sun55i-a523.c b/drivers/clk/sunxi-ng/ccu-sun55i-a523.c
index 979e53e63..4341eb66c 100644
--- a/drivers/clk/sunxi-ng/ccu-sun55i-a523.c
+++ b/drivers/clk/sunxi-ng/ccu-sun55i-a523.c
@@ -1667,6 +1667,17 @@ static const u32 pll_regs[] = {
 	SUN55I_A523_PLL_NPU_REG,
 };
 
+/*
+ * Park the GPU on the fixed pll-periph0-600M output while pll-gpu
+ * changes rate; the mux switch is glitch-free (T527 manual, GPU_CLK_REG).
+ */
+static struct ccu_mux_nb sun55i_a523_gpu_nb = {
+	.common		= &gpu_clk.common,
+	.cm		= &gpu_clk.mux,
+	.delay_us	= 1,
+	.bypass_index	= 1, /* pll-periph0-600M */
+};
+
 static int sun55i_a523_ccu_probe(struct platform_device *pdev)
 {
 	void __iomem *reg;
@@ -1698,6 +1709,10 @@ static int sun55i_a523_ccu_probe(struct platform_device *pdev)
 	if (ret)
 		return ret;
 
+	/* Reparent the GPU during pll-gpu rate changes */
+	ccu_mux_notifier_register(pll_gpu_clk.common.hw.clk,
+				  &sun55i_a523_gpu_nb);
+
 	return 0;
 }
 
-- 
2.47.3