[SeaBIOS] [PATCH 4/4] stacks: There is no need to disable NMI if it is already disabled

[Paolo Bonzini]

On 16/05/2017 18:14, Kevin O'Connor wrote:
> Don't write to the cmos index port on a mode switch if NMI is already
> disabled.  This reduces the number of outb() calls.
> 
> Signed-off-by: Kevin O'Connor <kevin at koconnor.net>
> ---
>  src/stacks.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/src/stacks.c b/src/stacks.c
> index f4d15ce..2fe1bfb 100644
> --- a/src/stacks.c
> +++ b/src/stacks.c
> @@ -66,8 +66,10 @@ call32_prep(u8 method)
>  
>      // Backup cmos index register and disable nmi
>      u8 cmosindex = inb(PORT_CMOS_INDEX);
> -    outb(cmosindex | NMI_DISABLE_BIT, PORT_CMOS_INDEX);
> -    inb(PORT_CMOS_DATA);
> +    if (!(cmosindex & NMI_DISABLE_BIT)) {
> +        outb(cmosindex | NMI_DISABLE_BIT, PORT_CMOS_INDEX);
> +        inb(PORT_CMOS_DATA);
> +    }
>      SET_LOW(Call16Data.cmosindex, cmosindex);
>  
>      SET_LOW(Call16Data.method, method);
> @@ -103,8 +105,11 @@ call32_post(void)
>      }
>  
>      // Restore cmos index register
> -    outb(GET_LOW(Call16Data.cmosindex), PORT_CMOS_INDEX);
> -    inb(PORT_CMOS_DATA);
> +    u8 cmosindex = GET_LOW(Call16Data.cmosindex);
> +    if (!(cmosindex & NMI_DISABLE_BIT)) {
> +        outb(cmosindex, PORT_CMOS_INDEX);
> +        inb(PORT_CMOS_DATA);
> +    }
>      return method;
>  }
>  
> 

NMI disable is actually a no-op on QEMU (as it never sends NMIs,
either), we might as well skip it in that case.

Paolo