Re: [PATCH V3 4/4] acpi/virt: suppress UART device & SPCR when guest has no serial hardware

[Sunil V L <sunilvl@ventanamicro.com>]

On Thu, May 15, 2025 at 08:44:39PM +0800, Li Chen wrote:
> From: Li Chen <chenl311@chinatelecom.cn>
> 
> The virt machines always instantiate a PL011/16550 at UART0 and
> describe it in ACPI (DSDT device node plus optional SPCR table).  When
> the command line contains “-serial none” there is no backend attached to
> that UART, yet the guest still discovers it via ACPI and may try to use
> it as a console, causing unexpected results.
> 
> Suggested-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
> ---
> 
>  hw/arm/virt-acpi-build.c   | 15 +++++++++------
>  hw/riscv/virt-acpi-build.c |  6 ++++--
>  include/system/system.h    |  2 ++
>  system/vl.c                |  5 +++++
>  4 files changed, 20 insertions(+), 8 deletions(-)
> 
> diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c
> index f25c3b26ce..8a1cde4b44 100644
> --- a/hw/arm/virt-acpi-build.c
> +++ b/hw/arm/virt-acpi-build.c
> @@ -59,6 +59,7 @@
>  #include "hw/acpi/viot.h"
>  #include "hw/virtio/virtio-acpi.h"
>  #include "target/arm/multiprocessing.h"
> +#include "system/system.h"
>  
>  #define ARM_SPI_BASE 32
>  
> @@ -825,11 +826,13 @@ build_dsdt(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms)
>       */
>      scope = aml_scope("\\_SB");
>      acpi_dsdt_add_cpus(scope, vms);
> -    acpi_dsdt_add_uart(scope, &memmap[VIRT_UART0],
> -                       (irqmap[VIRT_UART0] + ARM_SPI_BASE), 0);
> -    if (vms->second_ns_uart_present) {
> -        acpi_dsdt_add_uart(scope, &memmap[VIRT_UART1],
> -                           (irqmap[VIRT_UART1] + ARM_SPI_BASE), 1);
> +    if (serial_exist()) {
> +        acpi_dsdt_add_uart(scope, &memmap[VIRT_UART0],
> +                           (irqmap[VIRT_UART0] + ARM_SPI_BASE), 0);
> +        if (vms->second_ns_uart_present) {
> +            acpi_dsdt_add_uart(scope, &memmap[VIRT_UART1],
> +                               (irqmap[VIRT_UART1] + ARM_SPI_BASE), 1);
> +        }
>      }
>      if (vmc->acpi_expose_flash) {
>          acpi_dsdt_add_flash(scope, &memmap[VIRT_FLASH]);
> @@ -941,7 +944,7 @@ void virt_acpi_build(VirtMachineState *vms, AcpiBuildTables *tables)
>  
>      acpi_add_table(table_offsets, tables_blob);
>  
> -    if (ms->enable_spcr) {
> +    if (ms->enable_spcr && serial_exist()) {
>          spcr_setup(tables_blob, tables->linker, vms);
>      }
>  
> diff --git a/hw/riscv/virt-acpi-build.c b/hw/riscv/virt-acpi-build.c
> index 7f6d221c63..4e0f695a16 100644
> --- a/hw/riscv/virt-acpi-build.c
> +++ b/hw/riscv/virt-acpi-build.c
> @@ -39,6 +39,7 @@
>  #include "qapi/error.h"
>  #include "qemu/error-report.h"
>  #include "system/reset.h"
> +#include "system/system.h"
>  
>  #define ACPI_BUILD_TABLE_SIZE             0x20000
>  #define ACPI_BUILD_INTC_ID(socket, index) ((socket << 24) | (index))
> @@ -449,7 +450,8 @@ static void build_dsdt(GArray *table_data,
>                                   memmap[VIRT_APLIC_S].size, "RSCV0002");
>      }
>  
> -    acpi_dsdt_add_uart(scope, &memmap[VIRT_UART0], UART0_IRQ);
> +    if (serial_exist())
> +        acpi_dsdt_add_uart(scope, &memmap[VIRT_UART0], UART0_IRQ);
>  
>      if (socket_count == 1) {
>          virtio_acpi_dsdt_add(scope, memmap[VIRT_VIRTIO].base,
> @@ -681,7 +683,7 @@ static void virt_acpi_build(RISCVVirtState *s, AcpiBuildTables *tables)
>  
>      acpi_add_table(table_offsets, tables_blob);
>  
> -    if (ms->enable_spcr) {
> +    if (ms->enable_spcr && serial_exist()) {
>          spcr_setup(tables_blob, tables->linker, s);
>      }
>  
> diff --git a/include/system/system.h b/include/system/system.h
> index a7effe7dfd..ca1af38432 100644
> --- a/include/system/system.h
> +++ b/include/system/system.h
> @@ -75,6 +75,8 @@ extern unsigned int nb_prom_envs;
>  /* Return the Chardev for serial port i, or NULL if none */
>  Chardev *serial_hd(int i);
>  
> +bool serial_exist(void);
> +
>  /* parallel ports */
>  
>  #define MAX_PARALLEL_PORTS 3
> diff --git a/system/vl.c b/system/vl.c
> index 520956f4a1..7e219df7bf 100644
> --- a/system/vl.c
> +++ b/system/vl.c
> @@ -1484,6 +1484,11 @@ Chardev *serial_hd(int i)
>      return NULL;
>  }
>  
> +bool serial_exist(void)
> +{
> +    return serial_hd(0) ? true : false;
> +}
> +
LGTM.

Reviewed-by: Sunil V L <sunilvl@ventanamicro.com>