spi: Add Amlogic SPISG driver

Introduced support for the new SPI IP (SPISG) driver. The SPISG is
a communication-oriented SPI controller from Amlogic,supporting
three operation modes: PIO, block DMA, and scatter-gather DMA.

Due to there is no FIFO, PIO mode can only transfer one word at
a time, which is extremely slow. Therefore, this mode was not
implemented.

Signed-off-by: Sunny Luo <sunny.luo@amlogic.com>
Signed-off-by: Xianwei Zhao <xianwei.zhao@amlogic.com>
Link: https://patch.msgid.link/20250718-spisg-v5-2-b8f0f1eb93a2@amlogic.com
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/Kconfig

@@ -99,6 +99,15 @@ config SPI_AMLOGIC_SPIFC_A1
 	  This enables master mode support for the SPIFC (SPI flash
 	  controller) available in Amlogic A1 (A113L SoC).
 
+config SPI_AMLOGIC_SPISG
+	tristate "Amlogic SPISG controller"
+	depends on COMMON_CLK
+	depends on ARCH_MESON || COMPILE_TEST
+	help
+	  This enables master mode support for the SPISG (SPI scatter-gather
+	  communication controller), which is available on platforms such as
+	  Amlogic A4 SoCs.
+
 config SPI_APPLE
 	tristate "Apple SoC SPI Controller platform driver"
 	depends on ARCH_APPLE || COMPILE_TEST

drivers/spi/Makefile

@@ -20,6 +20,7 @@ obj-$(CONFIG_SPI_ALTERA)		+= spi-altera-platform.o
 obj-$(CONFIG_SPI_ALTERA_CORE)		+= spi-altera-core.o
 obj-$(CONFIG_SPI_ALTERA_DFL)		+= spi-altera-dfl.o
 obj-$(CONFIG_SPI_AMLOGIC_SPIFC_A1)	+= spi-amlogic-spifc-a1.o
+obj-$(CONFIG_SPI_AMLOGIC_SPISG)		+= spi-amlogic-spisg.o
 obj-$(CONFIG_SPI_APPLE)			+= spi-apple.o
 obj-$(CONFIG_SPI_AR934X)		+= spi-ar934x.o
 obj-$(CONFIG_SPI_ARMADA_3700)		+= spi-armada-3700.o