Linux serial tty driver for Raspberry Pi firmware UART #6502
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Add VideoCore mailbox definitions for the new RPi firmware UART. Signed-off-by: Tim Gover <[email protected]>
Assign a new serial core number for the RPi firmware UART. Signed-off-by: Tim Gover <[email protected]>
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On Raspberry Pi 4 and earlier models the firmware provides a low speed (up to 115200 baud) bit-bashed UART on arbitrary GPIOs using the second VPU core. The firmware driver is designed to support 19200 baud. Higher rates up to 115200 seem to work but there may be more jitter. This can be useful for debug or managing additional low speed peripherals if the hardware PL011 and 8250 hardware UARTs are already used for console / bluetooth. The firmware driver requires a fixed core clock frequency and also requires the VPU PWM audio driver to be disabled (dtparam=audio=off) Runtime configuration is handled via the vc-mailbox APIs with the FIFO buffers being allocated in uncached VPU addressable memory. The FIFO pointers are stored in spare VideoCore multi-core sync registers in order to reduce the number of uncached SDRAM accesses thereby reducing jitter. Signed-off-by: Tim Gover <[email protected]>
Enable the RPi firmware driver for Raspberry Pi4 and earlier models. Signed-off-by: Tim Gover <[email protected]>
Add a device-tree overlay to configure the GPIOs for the Raspberry Pi firmware UART. Example config.txt dtoverlay=rpi-fw-uart,txd0_pin=20,rxd0_pin=21 Signed-off-by: Phil Elwell <[email protected]> Signed-off-by: Tim Gover <[email protected]>
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See: raspberrypi/linux#6502 kernel: RP1 clocks See: raspberrypi/linux#6459 kernel: dts: bcm2712-rpi: For CM5IO, i2c_csi_dsi needs to be CAM/DISP1 See: raspberrypi/linux#6495 kernel: drm: vc4: dsi: Handle the different command FIFO widths See: raspberrypi/linux#6481
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See: raspberrypi/linux#6502 kernel: RP1 clocks See: raspberrypi/linux#6459 kernel: dts: bcm2712-rpi: For CM5IO, i2c_csi_dsi needs to be CAM/DISP1 See: raspberrypi/linux#6495 kernel: drm: vc4: dsi: Handle the different command FIFO widths See: raspberrypi/linux#6481
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The latest Raspberry Pi firmware (not released yet) adds support for a simple software UART on arbitrary GPIO pins. The implementation supports Pi4 family and older and requires exclusive access to the second VPU core.
Create a Linux driver for this using device-tree to configure the GPIOs
Firmware feature support
Recommended
config.txtsettings