On Fri, May 16, 2025 at 07:39:31AM +0000, Emmanuel Dreyfus wrote: > I have a Dell server with no serial port, and a serial console is highly > desirable for system administration. I wonder if EFI bootstrap could > be modified to use a serial port from a PCIe to serial card, or from a > USB to serial adapter.
Replying to myself to tell some succes. The UEFI bootstrap uses UEFI for serial I/O, hence we need UEFI to have a driver for the serial port in order to use it in NetBSD EFI bootstrap. There is such a driver for a unique USB-to-serial chip (VendorID 0x0403, productId 0x6001). The FtdiUsbSerialDxe driver can be (painfully) built from Tianocore/EDK2. The instruction are here. I only built OvmfPkg: https://github.com/tianocore/edk2-platforms Once done, I have: Build/OvmfX64/DEBUG_GCC/X64/Shell.efi Build/OptionRomPkg/DEBUG_GCC/X64/FtdiUsbSerialDxe.efi Shell.efi goes in EFI/boot on the EFI partition. FtdiUsbSerialDxe.efi goes wherever you want, for instance in EFI/EDK2 Next, I tell the machine to boot from file using EFI/boot/Shell.efi In the UEFI shell I type: FS0: load \EFI\EDK2\FtdiUsbSerialDxe.efi That causes a new serial port to be reported by the sermode command in the UEFI shell. I should be able to connect it to the UEFI console, but I got no success here. By typing bootx64.efi I exit the UEFI shell and load the NetBSD EFI bootstrap (the setps in UEFI shell can be made automatic using /EFI/boot/startup.nsh) The NetBSD EFI bootstrap looks up devices implementing the SerialIO protocol, and then filters out anything not on an EISA bus. I removed that filtering: --- eficons.c 14 Sep 2023 03:05:15 -0000 1.14 +++ eficons.c 4 Jun 2025 06:59:24 -0000 @@ -819,9 +819,13 @@ if (DevicePathType(dp) == ACPI_DEVICE_PATH && DevicePathSubType(dp) == ACPI_DP) { dpp = (EFI_DEV_PATH_PTR)dp; +#if 0 if (dpp.Acpi->HID == EISA_PNP_ID(0x0501)) { +#else + { +#endif uid = dpp.Acpi->UID; break; } } consdev now show only "pc com0" while the unpatched boostrap did show "pc com0 com1". But this single com0 is the right one. If I type consdev com0, I get a working serial console at 9600 bps. This is great, but the next step is booting the kernel. It does not support the console on the USB-to-serial adapter and I boot to multiuser without a console. Hence the new question is: do we have any hope of using a USB-to-serial adapter for kernel console? I have not looked at it yet, but I understand there will be the issue that the USB-to-serial adapter cannot work before a lot of devices initialization. It would be nice to have it working for single-user mode, and that should be possible. -- Emmanuel Dreyfus m...@netbsd.org
