clk: imx6: initialize GPU clocks

Initialize the GPU clock muxes to sane inputs. Until now they have
not been changed from their default values, which means that both
GPU3D shader and GPU2D core were fed by clock inputs whose rates
exceed the maximium allowed frequency of the cores by as much as
200MHz.

This fixes a severe GPU stability issue on i.MX6DL.

Cc: [e-mail]
Signed-off-by: Lucas Stach <[e-mail]>
Acked-by: Shawn Guo <[e-mail]>
Signed-off-by: Stephen Boyd <[e-mail]>

drivers/clk/imx/clk-imx6q.c

···
 	if (IS_ENABLED(CONFIG_PCI_IMX6))
 		clk_set_parent(clk[IMX6QDL_CLK_LVDS1_SEL], clk[IMX6QDL_CLK_SATA_REF_100M]);
 
+	/*
+	 * Initialize the GPU clock muxes, so that the maximum specified clock
+	 * rates for the respective SoC are not exceeded.
+	 */
+	if (clk_on_imx6dl()) {
+		clk_set_parent(clk[IMX6QDL_CLK_GPU3D_CORE_SEL],
+			       clk[IMX6QDL_CLK_PLL2_PFD1_594M]);
+		clk_set_parent(clk[IMX6QDL_CLK_GPU2D_CORE_SEL],
+			       clk[IMX6QDL_CLK_PLL2_PFD1_594M]);
+	} else if (clk_on_imx6q()) {
+		clk_set_parent(clk[IMX6QDL_CLK_GPU3D_CORE_SEL],
+			       clk[IMX6QDL_CLK_MMDC_CH0_AXI]);
+		clk_set_parent(clk[IMX6QDL_CLK_GPU3D_SHADER_SEL],
+			       clk[IMX6QDL_CLK_PLL2_PFD1_594M]);
+		clk_set_parent(clk[IMX6QDL_CLK_GPU2D_CORE_SEL],
+			       clk[IMX6QDL_CLK_PLL3_USB_OTG]);
+	}
+
 	imx_register_uart_clocks(uart_clks);
 }
 CLK_OF_DECLARE(imx6q, "fsl,imx6q-ccm", imx6q_clocks_init);