If DMA is not available (even when configured in DeviceTree), the driver will fail the startup procedure thus making serial console not available. For example this causes boot failure on QEMU ARMv7 (Exynos4210, SMDKC210): [ 1.302575] OF: amba_device_add() failed (-19) for /amba/pdma@12680000 ... [ 11.435732] samsung-uart 13800000.serial: DMA request failed [ 72.963893] samsung-uart 13800000.serial: DMA request failed [ 73.143361] Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000000 DMA is not necessary for serial to work, so continue with UART startup after emitting a warning.
Unified · Split
| @@ -1031,8 +1031,10 @@ static int s3c64xx_serial_startup(struct uart_port *port) · 1030 unmodified lines | ||
| 1031 | 1031 | if (ourport->dma) { |
| 1032 | 1032 | ret = s3c24xx_serial_request_dma(ourport); |
| 1033 | 1033 | if (ret < 0) { |
| 1034 | − dev_warn(port->dev, "DMA request failed\n"); | |
| 1035 | − return ret; | |
| 1034 | + dev_warn(port->dev, | |
| 1035 | + "DMA request failed, DMA will not be used\n"); | |
| 1036 | + devm_kfree(port->dev, ourport->dma); | |
| 1037 | + ourport->dma = NULL; | |
| 1036 | 1038 | } |
| 1037 | 1039 | } |
| 1038 | 1040 | |