Add support for ST7796 TFT LCD controller (320x480). The driver
implements the NuttX framebuffer interface for SPI-connected displays.
Features:
- SPI interface with CONFIG_SPI_CMDDATA for D/C pin control;
- RGB565 (16-bit) and RGB666 (18-bit) color formats;
- Runtime rotation support (0, 90, 180, 270 degrees) via MADCTL;
- Board-provided configuration via st7796_config_s structure;
- Partial screen update via updatearea for efficient rendering;
- Persistent swap buffer to avoid per-frame allocations;
- Proper ST7796S initialization sequence with documented timing;
The driver uses a board-provided configuration structure allowing
flexible setup of resolution, SPI frequency, color depth, and
initial MADCTL value without requiring Kconfig options in the
generic driver.
Architecture changes in this revision as per request:
- Moved internal register commands to .c file (private)
- Moved MADCTL bit definitions to .c file (private)
- Moved struct st7796_cmd_s to .c file (private)
- Converted MADCTL orientation macros to absolute values
- Moved CONFIG_SPI_CMDDATA error check to beginning of file
- Removed duplicated CONFIG_SPI_CMDDATA guards
- Public header contains only board configuration API
- Changed the Kconfig auto-select FB from 'select' to 'depends on'
Tested with LVGL graphics library on STM32H753ZI board (my own port).
Signed-off-by: Vinicius May <vmay.sweden@gmail.com>
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