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1. Linux kernel is 5.10 cip13-rt5, VLP3.0.1.
2. RZ/G2L SMARC board is used.
3. SCIF2 is used.
4. SCIF DMA must be disabled(using PIO mode).
5. RTS pin of SCIF2 is used as the GPIO.

DMA disabling:

From VLP3.0.3 and later, the DMA for SCIF is enabled by default. It must be disabled in device tree:

--- a/arch/arm64/boot/dts/renesas/r9a07g044.dtsi
+++ b/arch/arm64/boot/dts/renesas/r9a07g044.dtsi
@@ -415,8 +415,8 @@ scif2: serial@1004c000 {
                       "bri", "dri", "tei";
             clocks = <&cpg CPG_MOD R9A07G044_SCIF2_CLK_PCK>;
             clock-names = "fck";
-            dmas = <&dmac 0x4e81>, <&dmac 0x4e82>;
-            dma-names = "tx", "rx";
+            /*dmas = <&dmac 0x4e81>, <&dmac 0x4e82>;
+            dma-names = "tx", "rx";*/
             power-domains = <&cpg>;
             resets = <&cpg R9A07G044_SCIF2_RST_SYSTEM_N>;
             status = "disabled";

arch/arm64/boot/dts/renesas/rzg2l-smarc-pinfunction.dtsi

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