Re: [Qemu-devel] [RFC] arm/virt: add one more uart for UEFI runtime debug

[Peter Maydell <peter.maydell@linaro.org>]

On Sun, 7 Apr 2019 at 09:19, Heyi Guo <guoheyi@huawei.com> wrote:
>
> This patch is based on the discussion in TianoCore edk2-devel mailing
> list:
> https://lists.01.org/pipermail/edk2-devel/2019-March/037986.html
>
> The conclusion is that we need an individual UART for UEFI runtime
> services to print debug message at runtime, to avoid conflicting with
> the system UART. We cannot use the secure UART either, for we may both
> have Trusted Firmware and UEFI runtime services running on the VM, and
> it is not easy to keep synchronization between the two components.

I don't think it makes much sense to keep adding UARTs for every
bit of the system software stack. We don't have an infinite
supply of UARTs on real hardware either -- how is this handled
there ?

Also adding new UARTs to this board is awkward because of
the weird choices various bits of software have made in
reading the dtb and picking a UART if there's more than one
listed.

> @@ -713,13 +715,23 @@ static void create_uart(const VirtMachineState *vms, qemu_irq *pic, int uart,
>      if (uart == VIRT_UART) {
>          qemu_fdt_setprop_string(vms->fdt, "/chosen", "stdout-path", nodename);
>      } else {
> +        const char *status_string;
> +
> +        if (uart == VIRT_SECURE_UART) {
> +            status_string = "secure-status";
> +        } else {
> +            status_string = "uefi-status";

Where does this status string come from? The "secure-status" one
is documented in the device tree spec and has a well defined
meaning.

thanks
-- PMM