SPI

The Serial Peripheral Interface (SPI) is a synchronous, full-duplex, 4-wire serial bus.

Signals

Signal	Description
MOSI	Controller data output, target data input
MISO	Controller data input, target data output
SCLK	Clock generated by the controller
CS	Chip-select (active low); up to 4 chip-select lines per bus

Transfer Modes by Subsystem

Subsystem	Transfer Modes	Max Speed	Notes
Linux	FIFO, CPU DMA, GSI	50 MHz	4–32 bits per word; up to 4 CS
Boot	FIFO only	50 MHz	Polling mode; GSI not supported
aDSP	Full/half duplex, synchronous	50 MHz	Raw bit-level; no framing or error checking

Interface Components

Device Tree Sources

Platform	File
Dragonwing IQ-8275	`arch/arm64/boot/dts/qcom/qcs8300.dtsi`

APIs

Subsystem	Header
Linux	`include/uapi/linux/spi/spidev.h`, `include/linux/spi/spi.h`
Boot	`boot_images/boot/QcomPkg/Include/SpiApi.h`
aDSP	`adsp_proc/core/api/buses/spi_api.h`

Software Configuration

Linux Device Tree Example

spi@a98000 {
    compatible = "qcom,geni-spi";
    reg = <0 0x00a98000 0 0x4000>;
    clocks = <&gcc GCC_QUPV3_WRAP1_S6_CLK>;
    clock-names = "se";
    pinctrl-names = "default";
    pinctrl-0 = <&qup_spi14_data_clk>, <&qup_spi14_cs>;
    interrupts = <GIC_SPI 368 IRQ_TYPE_LEVEL_HIGH>;
    #address-cells = <1>;
    #size-cells = <0>;
    power-domains = <&rpmhpd SA8295P_CX>;
    dmas = <&gpi_dma1 0 6 QCOM_GPI_SPI>,
           <&gpi_dma1 1 6 QCOM_GPI_SPI>;
    dma-names = "tx", "rx";
    status = "disabled";
};

QUPAC Access Control

{ QUPV3_0_SE3, QUPV3_PROTOCOL_SPI, QUPV3_MODE_FIFO, AC_HLOS, TRUE,  TRUE, FALSE },
{ QUPV3_1_SE3, QUPV3_PROTOCOL_SPI, QUPV3_MODE_FIFO, AC_HLOS, FALSE, TRUE, TRUE  },
{ QUPV3_1_SE4, QUPV3_PROTOCOL_SPI, QUPV3_MODE_GSI,  AC_TZ,   FALSE, TRUE, TRUE  },
{ QUPV3_1_SE6, QUPV3_PROTOCOL_SPI, QUPV3_MODE_GSI,  AC_HLOS, FALSE, TRUE, FALSE },

Configuration Steps

Enable kernel configurations

Edit kernel_platform/kernel/arch/arm64/configs/qcom_defconfig:

CONFIG_QCOM_GENI_SE=y
CONFIG_SPI_QCOM_GENI=m
CONFIG_SPI_SPIDEV=m
CONFIG_QCOM_GPI_DMA=m

Enable SPI node in device tree

&spi1 {
    status = "okay";
};

Compile and flash

Compile the kernel and device tree changes, then load images to the device.

Verification

Compile SPI utility tool

The spidev_test.c utility is available in the Linux kernel source tree under tools/spi/. It is a simple SPI test program that uses the spidev driver and can be compiled either from the kernel source tree or from a standalone copy.Ensure the build directory contains the following files:

spidev_test.c
Makefile

On an Ubuntu build host, install the cross-compiler:

sudo apt-get update
sudo apt-get install gcc-aarch64-linux-gnu

Set the cross-compilation environment:

export ARCH=arm64
export CROSS_COMPILE=aarch64-linux-gnu-

Compile spidev_test:

make

Transfer spidev_test to device

scp spidev_test root@<IP address>:/usr
chmod 777 /usr/spidev_test

Run test

./spidev_test -D /dev/spidev1.0

Expected output:

spi mode: 0x0
bits per word: 8
max speed: 500000 Hz (500 KHz)

Debugging

sudo su
mount -t debugfs none /sys/kernel/debug
echo -n "file spi-geni-qcom.c +p" > /sys/kernel/debug/dynamic_debug/control
echo -n "file spidev.c +p" > /sys/kernel/debug/dynamic_debug/control
echo -n "file gpi.c +p" > /sys/kernel/debug/dynamic_debug/control

Troubleshooting

SPI Device Not Detected

zcat /proc/config.gz | grep -E 'CONFIG_SPI_SPIDEV|CONFIG_SPI_QCOM_GENI'
dmesg | grep -i spi

Verify SPI node status is "okay" in device tree
Verify QUPAC_Access.c sets QUPV3_PROTOCOL_SPI, AC_HLOS, bLoad=TRUE

SPI Transfer Failures

./spidev_test -D /dev/spidev1.0 -s 1000000

Check GPIO drive strength and pull configuration
Verify clock phase and polarity match the target device

GSI/DMA Mode Not Working

Verify CONFIG_QCOM_GPI_DMA=m
Check dmas and dma-names in device tree
Verify QUPAC_Access.c sets QUPV3_MODE_GSI

IQ-8275 EVK