I2S_MCUX: Fixup I2S MCUX Audio PLL Rate Calculation and Reg Writes

This PR Fixes the Audio PLL Rate Calculation (there was an additional
divide / 8 which is not necessary and does not appear in similar
calculations in example code from the SDK).

Additionally, it adjusts the SAI .dtsi to more correctly configure the
mclk rate, and adds comments specifying what the regististers mean.

Signed-off-by: Nickolas Lapp <[email protected]>

Author: NickolasLapp

drivers/clock_control/clock_control_mcux_ccm.c

@@ -176,17 +176,17 @@ static int mcux_ccm_get_subsys_rate(const struct device *dev,
 
 #ifdef CONFIG_I2S_MCUX_SAI
 	case IMX_CCM_SAI1_CLK:
-		*rate = CLOCK_GetFreq(kCLOCK_AudioPllClk) / 8
+		*rate = CLOCK_GetFreq(kCLOCK_AudioPllClk)
 				/ (CLOCK_GetDiv(kCLOCK_Sai1PreDiv) + 1)
 				/ (CLOCK_GetDiv(kCLOCK_Sai1Div) + 1);
 		break;
 	case IMX_CCM_SAI2_CLK:
-		*rate = CLOCK_GetFreq(kCLOCK_AudioPllClk) / 8
+		*rate = CLOCK_GetFreq(kCLOCK_AudioPllClk)
 				/ (CLOCK_GetDiv(kCLOCK_Sai2PreDiv) + 1)
 				/ (CLOCK_GetDiv(kCLOCK_Sai2Div) + 1);
 		break;
 	case IMX_CCM_SAI3_CLK:
-		*rate = CLOCK_GetFreq(kCLOCK_AudioPllClk) / 8
+		*rate = CLOCK_GetFreq(kCLOCK_AudioPllClk)
 				/ (CLOCK_GetDiv(kCLOCK_Sai3PreDiv) + 1)
 				/ (CLOCK_GetDiv(kCLOCK_Sai3Div) + 1);
 		break;

dts/arm/nxp/nxp_rt.dtsi

@@ -937,19 +937,32 @@
 			#pinmux-cells = <2>;
 			reg = <0x40384000 0x4000>;
 			clocks = <&ccm IMX_CCM_SAI1_CLK 0x7C 2>;
-			pre-div = <0>;
-			podf = <63>;
-			pll-clocks = <&anatop 0x70 0xC000 0>,
-					<&anatop 0x70 0x7F 32>,
-					<&anatop 0x70 0x18 1>,
-					<&anatop 0x80 0x3FFFFFFF 77>,
-					<&anatop 0x90 0x3FFFFFFF 100>;
+			/* Audio PLL Output Frequency is determined by:
+			 * (Fref * (DIV_SELECT + NUM/DENOM)) / POST_DIV
+			 * = (24MHz * (32 + 77 / 100)) / 1 = 786.48 MHz
+			 */
+		       pll-clocks = <&anatop 0x70 0xC000 0>,
+				      <&anatop 0x70 0x7F 32>,
+				      <&anatop 0x70 0x180000 1>,
+				      <&anatop 0x80 0x3FFFFFFF 77>,
+				      <&anatop 0x90 0x3FFFFFFF 100>;
 			pll-clock-names = "src", "lp", "pd", "num", "den";
+			/* The maximum input frequency into the SAI mclk input is 300MHz
+			 * Based on this requirement, pre-div must be at least 3
+			 * The pre-div and post-div are one less than the actual divide-by amount.
+			 * A pre-div value of 0x1 results in a pre-divider of
+			 * (1+1) = 2
+			 */
+			pre-div = <0x3>;
+			podf = <0x0F>;
 			pinmuxes = <&iomuxcgpr 0x4 0x80000>;
 			interrupts = <56 0>;
 			dmas = <&edma0 0 19>, <&edma0 0 20>;
 			dma-names = "rx", "tx";
-			nxp,tx-channel = <0>;
+			/* This translates to SAIChannelMask (fsl_sai.c) and
+			 * cannot be 0
+			 */
+			nxp,tx-channel = <1>;
 			nxp,tx-dma-channel = <0>;
 			nxp,rx-dma-channel = <1>;
 			status = "disabled";
@@ -965,11 +978,11 @@
 			clocks = <&ccm IMX_CCM_SAI2_CLK 0x7C 2>;
 			pre-div = <0>;
 			podf = <63>;
-			pll-clocks = <&anatop 0x70 0xC000 0>,
-				   <&anatop 0x70 0x7F 32>,
-				   <&anatop 0x70 0x18 1>,
-				   <&anatop 0x80 0x3FFFFFFF 77>,
-				   <&anatop 0x90 0x3FFFFFFF 100>;
+			pll-clocks = <&anatop 0x70 0xC000 0x0>,
+					<&anatop 0x70 0x7F 32>,
+					<&anatop 0x70 0x180000 1>,
+					<&anatop 0x80 0x3FFFFFFF 77>,
+					<&anatop 0x90 0x3FFFFFFF 100>;
 			pll-clock-names = "src", "lp", "pd", "num", "den";
 			pinmuxes = <&iomuxcgpr 0x4 0x100000>;
 			interrupts = <57 0>;
@@ -993,7 +1006,7 @@
 			podf = <63>;
 			pll-clocks = <&anatop 0x70 0xC000 0>,
 				   <&anatop 0x70 0x7F 32>,
-				   <&anatop 0x70 0x18 1>,
+				   <&anatop 0x70 0x180000 1>,
 				   <&anatop 0x80 0x3FFFFFFF 77>,
 				   <&anatop 0x90 0x3FFFFFFF 100>;
 			pll-clock-names = "src", "lp", "pd", "num", "den";