clk: sunxi-ng: a64: stop force-selecting PLL-MIPI as TCON0 parent

Stop force-selecting PLL-MIPI as TCON0 parent, since it breaks video
output on Pinebook that uses RGB to eDP bridge.

Partially revert commit ca1170b ("clk: sunxi-ng: a64: force
select PLL_MIPI in TCON0 mux"), while still leaving
CLK_SET_RATE_NO_REPARENT flag set, since we do not want the clock to
be reparented.

The issue is that apparently different TCON0 outputs require a different
clock, or the mux might be selecting the output type.

I did an experiment: I manually configured PLL_MIPI and PLL_VIDEO0_2X
to the same clock rate and flipped the switch with devmem. Experiment
clearly showed that whenever PLL_MIPI is selected as TCON0 clock parent,
the video output stops working.

Therefore, TCON0 clock parent corresponding to the output type must be
assigned in the device tree.

Fixes: ca1170b ("clk: sunxi-ng: a64: force select PLL_MIPI in TCON0 mux")
Reviewed-by: Dragan Simic <[email protected]>
Reviewed-by: Chen-Yu Tsai <[email protected]>
Tested-by: Frank Oltmanns <[email protected]> # on PinePhone
Tested-by: Stuart Gathman <[email protected]> # on OG Pinebook
Signed-off-by: Vasily Khoruzhick <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Chen-Yu Tsai <[email protected]>

Author: anarsoul

drivers/clk/sunxi-ng/ccu-sun50i-a64.c

@@ -535,11 +535,11 @@ static SUNXI_CCU_M_WITH_MUX_GATE(de_clk, "de", de_parents,
 				 CLK_SET_RATE_PARENT);
 
 /*
- * DSI output seems to work only when PLL_MIPI selected. Set it and prevent
- * the mux from reparenting.
+ * Experiments showed that RGB output requires pll-video0-2x, while DSI
+ * requires pll-mipi. It will not work with incorrect clock, the screen will
+ * be blank.
+ * sun50i-a64.dtsi assigns pll-mipi as TCON0 parent by default
  */
-#define SUN50I_A64_TCON0_CLK_REG	0x118
-
 static const char * const tcon0_parents[] = { "pll-mipi", "pll-video0-2x" };
 static const u8 tcon0_table[] = { 0, 2, };
 static SUNXI_CCU_MUX_TABLE_WITH_GATE_CLOSEST(tcon0_clk, "tcon0", tcon0_parents,
@@ -959,11 +959,6 @@ static int sun50i_a64_ccu_probe(struct platform_device *pdev)
 
 	writel(0x515, reg + SUN50I_A64_PLL_MIPI_REG);
 
-	/* Set PLL MIPI as parent for TCON0 */
-	val = readl(reg + SUN50I_A64_TCON0_CLK_REG);
-	val &= ~GENMASK(26, 24);
-	writel(val | (0 << 24), reg + SUN50I_A64_TCON0_CLK_REG);
-
 	ret = devm_sunxi_ccu_probe(&pdev->dev, reg, &sun50i_a64_ccu_desc);
 	if (ret)
 		return ret;