On 03/01/19 16:09, Peter Maydell wrote: > On Fri, 1 Mar 2019 at 14:59, Laszlo Ersek <ler...@redhat.com> wrote: >> >> +Peter >> >> On 03/01/19 13:24, Heyi Guo wrote: >>> On 2019/2/28 21:39, Laszlo Ersek wrote: >> >>>> (4) What's most worrying is that this change would lead to an unexpected >>>> sharing of the PL011 device between the OS and the firmware. I don't >>>> think that's a great idea, especially if QEMU's ACPI payload explicitly >>>> advertises the port to the OS. >>> That's true, so I propose to disable the feature by default. It is only >>> used for UEFI runtime code debug. It is always painful when we don't a >>> handy debug tool for runtime services code. >> >> I think this is the only problem that we have at the design level. >> >> What I'd like to understand is whether it is safe to drive the PL011 >> serial port from both the firmware and the kernel. > > I would suggest that it probably is not safe. Certainly it > does not seem likely to be robust against all possible future > changes to the kernel's driver and/or the firmware's driver. > >> This is why I'm not a big fan of this approach. Using separate devices >> for kernel and firmware would be a lot better. >> >> I remember that Peter did some work to enable two PL011 devices on the >> "virt" board. IIRC the issue was that the PL011 enumeration order / >> numbering in edk2, and in the Linux (guest) kernel, was exactly the >> opposite. And that caused both logs to go to different devices; you >> couldn't have a single log file that started with the firmware log, and >> continued (after a definite switch-over) with the kernel log. > > Yes, that's basically it (I forget the exact details and it's the > kind of thing that may well depend on exactly what version of the > kernel or what version of the firmware you were using). I do still > have a todo list item to add a 2nd UART (probably "if the user > specifically asked for it with an extra -serial option"), but > we can't just add it to the board by default.
Thanks for the info! > Note that if you are using QEMU under emulation where it is emulating > EL3 then you always get a second UART which is visible only to the > secure world. This is specifically intended for firmware to use. The ArmVirtQemu firmware doesn't handle the secure world at all (yet?). Thanks Laszlo _______________________________________________ edk2-devel mailing list edk2-devel@lists.01.org https://lists.01.org/mailman/listinfo/edk2-devel
