Re: [Qemu-devel] [PATCH] ARM: Virt: Don't generate RTC ACPI node when using UEFI

[Laszlo Ersek]

On 01/12/16 16:24, Shannon Zhao wrote:
> When booting VM through UEFI, UEFI takes ownership of the RTC hardware.
> To DTB UEFI could call libfdt api to disable the RTC device node, but to
> ACPI it couldn't do that. Therefore, we don't generate the RTC ACPI
> device in QEMU when using UEFI.
> 
> Signed-off-by: Shannon Zhao <address@hidden>
> ---
>  hw/arm/virt-acpi-build.c         | 13 +++++++++++--
>  hw/arm/virt.c                    |  5 ++++-
>  include/hw/arm/virt-acpi-build.h |  1 +
>  3 files changed, 16 insertions(+), 3 deletions(-)
> 
> diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c
> index 0caf5ce..cccec79 100644
> --- a/hw/arm/virt-acpi-build.c
> +++ b/hw/arm/virt-acpi-build.c
> @@ -575,8 +575,17 @@ build_dsdt(GArray *table_data, GArray *linker, 
> VirtGuestInfo *guest_info)
>      acpi_dsdt_add_cpus(scope, guest_info->smp_cpus);
>      acpi_dsdt_add_uart(scope, &memmap[VIRT_UART],
>                         (irqmap[VIRT_UART] + ARM_SPI_BASE));
> -    acpi_dsdt_add_rtc(scope, &memmap[VIRT_RTC],
> -                      (irqmap[VIRT_RTC] + ARM_SPI_BASE));
> +
> +    /* When booting VM through UEFI, UEFI takes ownership of the RTC 
> hardware.
> +     * To DTB UEFI could call libfdt api to disable the RTC device node, but 
> to
> +     * ACPI it couldn't do that. Therefore, we don't generate the RTC ACPI
> +     * device here when using UEFI.
> +     */
> +    if (guest_info->acpi_rtc) {
> +        acpi_dsdt_add_rtc(scope, &memmap[VIRT_RTC],
> +                          (irqmap[VIRT_RTC] + ARM_SPI_BASE));
> +    }
> +
>      acpi_dsdt_add_flash(scope, &memmap[VIRT_FLASH]);
>      acpi_dsdt_add_virtio(scope, &memmap[VIRT_MMIO],
>                      (irqmap[VIRT_MMIO] + ARM_SPI_BASE), 
> NUM_VIRTIO_TRANSPORTS);
> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> index fd52b76..de12037 100644
> --- a/hw/arm/virt.c
> +++ b/hw/arm/virt.c
> @@ -1002,6 +1002,7 @@ static void machvirt_init(MachineState *machine)
>      VirtGuestInfoState *guest_info_state = g_malloc0(sizeof 
> *guest_info_state);
>      VirtGuestInfo *guest_info = &guest_info_state->info;
>      char **cpustr;
> +    bool firmware_loaded;
>  
>      if (!cpu_model) {
>          cpu_model = "cortex-a15";
> @@ -1124,12 +1125,14 @@ static void machvirt_init(MachineState *machine)
>      create_fw_cfg(vbi, &address_space_memory);
>      rom_set_fw(fw_cfg_find());
>  
> +    firmware_loaded = bios_name || drive_get(IF_PFLASH, 0, 0);
>      guest_info->smp_cpus = smp_cpus;
>      guest_info->fw_cfg = fw_cfg_find();
>      guest_info->memmap = vbi->memmap;
>      guest_info->irqmap = vbi->irqmap;
>      guest_info->use_highmem = vms->highmem;
>      guest_info->gic_version = gic_version;
> +    guest_info->acpi_rtc = !firmware_loaded;
>      guest_info_state->machine_done.notify = virt_guest_info_machine_done;
>      qemu_add_machine_init_done_notifier(&guest_info_state->machine_done);
>  
> @@ -1141,7 +1144,7 @@ static void machvirt_init(MachineState *machine)
>      vbi->bootinfo.board_id = -1;
>      vbi->bootinfo.loader_start = vbi->memmap[VIRT_MEM].base;
>      vbi->bootinfo.get_dtb = machvirt_dtb;
> -    vbi->bootinfo.firmware_loaded = bios_name || drive_get(IF_PFLASH, 0, 0);
> +    vbi->bootinfo.firmware_loaded = firmware_loaded;
>      arm_load_kernel(ARM_CPU(first_cpu), &vbi->bootinfo);
>  
>      /*
> diff --git a/include/hw/arm/virt-acpi-build.h 
> b/include/hw/arm/virt-acpi-build.h
> index 744b666..6f412a4 100644
> --- a/include/hw/arm/virt-acpi-build.h
> +++ b/include/hw/arm/virt-acpi-build.h
> @@ -33,6 +33,7 @@ typedef struct VirtGuestInfo {
>      const int *irqmap;
>      bool use_highmem;
>      int gic_version;
> +    bool acpi_rtc;
>  } VirtGuestInfo;
>  
>  
> 

I realize that Peter is not buying the argument just yet, but I'd like
to offer a review here nonetheless.

I think the patch is good, except the location and the wording of the
code comment.

(1) The code comment should be located right above the

    guest_info->acpi_rtc = !firmware_loaded;

assignment.

(2) I think the code comment should simply use indicative mood:

    When booting the VM with UEFI, UEFI takes ownership of the RTC
    hardware. While UEFI can use libfdt to disable the RTC device node
    in the DTB that it passes to the OS, it cannot modify AML.
    Therefore, we won't generate the RTC ACPI device at all when using
    UEFI.

With those changes, I'm willing to R-b.

Thanks
Laszlo