zynq spi dts

### Zynq SPI Device Tree Configuration (DTS) For configuring SPI devices on the Zynq platform using the device tree, specific entries must be made within the `.dts` file that describe the hardware components and their connections. The following example demonstrates how to define an SPI controller along with connected peripherals: ```dts spi0: spi@e0007000 { compatible = "xlnx,zynq-spi-1.0"; reg = <0xe0007000 0x1000>; interrupts = <0 29 4>; num-cs = <1>; /* Number of chip selects */ status = "okay"; spidev@0 { /* Example peripheral attached via SPI */ compatible = "spidev"; reg = <0>; /* Chip select number */ spi-max-frequency = <50000000>; status = "okay"; }; }; ``` This snippet defines an SPI controller located at address `0xe0007000`, specifies its interrupt line, sets up one chip-select line (`num-cs`) for selecting slave devices, and includes a simple SPI device as an example[^2]. The configuration allows developers to specify parameters such as maximum frequency supported by the SPI bus or individual slaves through properties like `spi-max-frequency`. Additionally, each child node under the SPI controller represents different SPI-connected peripherals. When working with Zynq platforms containing FPGAs configured from SD cards upon powering on, ensuring proper setup in the device tree facilitates communication between software layers and underlying hardware resources. #### CMA Configuration Impact In contexts where Direct Memory Access (DMA) operations are involved—such as when transferring data over SPI—it may also become necessary to adjust Contiguous Memory Allocator (CMA) settings during system initialization to reserve sufficient contiguous blocks of RAM required for efficient transfers without fragmentation issues[^3].