Re: [SeaBIOS] [PATCHv2] acpi: make default DSDT optional

[Laszlo Ersek]

comments in-line

On 03/18/13 11:12, Michael S. Tsirkin wrote:
> QEMU now loads its own copy of DSDT, so let's not build in PIIX.
> This leaves building in the DSDT an option, default to off.
> If no one complains for a while, we'll be able to
> remove this altogether.
> Signed-off-by: Michael S. Tsirkin
>
> Changes from v1:
> default the new option to y to reduce
> disruption to existing users
>
> src/Kconfig | 6 ++++++
>  src/acpi.c  | 7 ++++++-
>  2 files changed, 12 insertions(+), 1 deletion(-)

The acpi_setup() function already picks the qemu-exported DSDT if there
is one: fill_dsdt() links it into the FADT, and then we won't
malloc_high() an area for our own copy.

What is the purpose of this patch? Is it to save space? I assume the
static AmlCode array from "acpi-dsdt.hex" only occupies RAM as long as
we don't start the boot loader / OS, so it is not important for runtime.
Do we want to save space in the binary?
> diff --git a/src/Kconfig b/src/Kconfig
> index 3141069..655ab1c 100644
> --- a/src/Kconfig
> +++ b/src/Kconfig
> @@ -387,6 +387,12 @@ menu "BIOS Tables"
>          default y
>          help
>              Support generation of ACPI tables.
> config ACPI_DSDT
>    bool "Include default ACPI DSDT"
>    default y
> depends on ACPI
>    help
>        Include default DSDT ACPI table in BIOS.
>
> endmenu
>
> source vgasrc/Kconfig

I think if ACPI_DSDT is off, then the Makefile could elect not to build
"acpi-dsdt.hex" at all. (The "$(OUT)acpi.o" target should not depend on
"acpi-dsdt.hex" in that case.) Anyway extra work is not a bug of course.
(Plus I'm not sure how we could pass in the config value for ifeq.)
> diff --git a/src/acpi.c b/src/acpi.c
> index 119d1c1..69dd3aa 100644
> --- a/src/acpi.c
> +++ b/src/acpi.c
> @@ -202,7 +202,11 @@ struct srat_memory_affinity
>      u32    reserved3[2];
>  } PACKED;
>
> +#ifdef CONFIG_ACPI_DSDT

The macro CONFIG_ACPI_DSDT is always defined (you use it just below in a
controlling expression); its value is what varies.
> #include "acpi-dsdt.hex"
> +#else
> +static u8 AmlCode[1];
> +#endif
>
> static void
>  build_header(struct acpi_table_header *h, u32 sig, int len, u8 rev)
> @@ -826,7 +830,8 @@ acpi_setup(void)
>              break;
>          }
>      }
> if (fadt && !fadt->dsdt) {
> if (fadt && !fadt->dsdt && CONFIG_ACPI_DSDT) {
>     /* default DSDT */
>     void *dsdt = malloc_high(sizeof(AmlCode));
>     if (!dsdt) {

For short-circuiting hygiene I'd put the config option first.

Laszlo