[PATCH v2 5/5] hw: aspeed: Init all UART's with serial devices

[Cédric Le Goater]

On 5/16/22 08:23, Peter Delevoryas wrote:
> Background:
> 
> AspeedMachineClass.uart_default specifies the serial console UART, which
> usually corresponds to the "stdout-path" in the device tree.
> 
> The default value is UART5, since most boards use UART5 for this:
> 
>      amc->uart_default = ASPEED_DEV_UART5;
> 
> Users can override AspeedMachineClass.uart_default in their board's machine
> class init to specify something besides UART5. For example, for fuji-bmc:
> 
>      amc->uart_default = ASPEED_DEV_UART1;
> 
> We only connect this one UART, of the 5 UART's on the AST2400 and AST2500
> and the 13 UART's on the AST2600 and AST1030, to a serial device that QEMU
> users can use. None of the other UART's are initialized, and the only way
> to override this attribute is by creating a specialized board definition,
> requiring QEMU source code changes and rebuilding.
> 
> The result of this is that if you want to get serial console output on a
> board that uses UART3, you need to add a board definition. This was
> encountered by Zev in OpenBMC. [1]
> 
> Changes:
> 
> This commit initializes all of the UART's present on each Aspeed chip with
> serial devices and allows the QEMU user to connect as many or few as they
> like to serial devices. For example, you can still run QEMU and just connect
> stdout to the machine's default UART, without specifying any additional
> serial devices:
> 
>      qemu-system-arm -machine fuji-bmc \
>          -drive file=fuji.mtd,format=raw,if=mtd \
>          -nographic
> 
> However, if you don't want to add a special machine definition, you can now
> manually configure UART1 to connect to stdout and get serial console output,
> even if the machine's default is UART5:
> 
>      qemu-system-arm -machine ast2600-evb \
>          -drive file=fuji.mtd,format=raw,if=mtd \
>          -serial null -serial mon:stdio -display none
> 
> In the example above, the first "-serial null" argument is connected to
> UART5, and "-serial mon:stdio" is connected to UART1.
> 
> Another example: you can get serial console output from Wedge100, which uses
> UART3, by reusing the palmetto AST2400 machine and rewiring the serial
> device arguments:
> 
>      qemu-system-arm -machine palmetto-bmc \
>          -drive file=wedge100.mtd,format=raw,if=mtd \
>          -serial null -serial null -serial null \
>          -serial mon:stdio -display none
> 
> There is a slight change in behavior introduced with this change: now, each
> UART's memory-mapped IO region will have a serial device model connected to
> it. Previously, all reads and writes to those regions would be ineffective
> and return zero values, but now some values will be nonzero, even when the
> user doesn't connect a serial device backend (like a socket, file, etc). For
> example, the line status register might indicate that the transmit buffer is
> empty now, whereas previously it might have always indicated it was full.
> 
> [1] https://lore.kernel.org/openbmc/YnzGnWjkYdMUUNyM@hatter.bewilderbeest.net/
> [2] https://github.com/facebook/openbmc/releases/download/v2021.49.0/fuji.mtd
> [3] https://github.com/facebook/openbmc/releases/download/v2021.49.0/wedge100.mtd
> 
> Signed-off-by: Peter Delevoryas <pdel at fb.com>


Reviewed-by: Cédric Le Goater <clg at kaod.org>

Thanks,

C.


> ---
>   hw/arm/aspeed_soc.c | 9 +++++++++
>   1 file changed, 9 insertions(+)
> 
> diff --git a/hw/arm/aspeed_soc.c b/hw/arm/aspeed_soc.c
> index 912798a9c9..30574d4276 100644
> --- a/hw/arm/aspeed_soc.c
> +++ b/hw/arm/aspeed_soc.c
> @@ -546,9 +546,18 @@ qemu_irq aspeed_soc_get_irq(AspeedSoCState *s, int dev)
>   void aspeed_soc_uart_init(AspeedSoCState *s)
>   {
>       AspeedSoCClass *sc = ASPEED_SOC_GET_CLASS(s);
> +    int i, uart;
>   
>       /* Attach an 8250 to the IO space as our UART */
>       serial_mm_init(get_system_memory(), sc->memmap[s->uart_default], 2,
>                      aspeed_soc_get_irq(s, s->uart_default), 38400,
>                      serial_hd(0), DEVICE_LITTLE_ENDIAN);
> +    for (i = 1, uart = ASPEED_DEV_UART1; i < sc->uarts_num; i++, uart++) {
> +        if (uart == s->uart_default) {
> +            uart++;
> +        }
> +        serial_mm_init(get_system_memory(), sc->memmap[uart], 2,
> +                       aspeed_soc_get_irq(s, uart), 38400,
> +                       serial_hd(i), DEVICE_LITTLE_ENDIAN);
> +    }
>   }