Re: [PATCH v1 12/28] x86: apic: use APIC_EIO_ACK instead of open-coded 0

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 05/11/2026 1:33 am, dmukhin@ford.com wrote:
> From: Denis Mukhin <dmukhin@ford.com>
>
> Use the symbolic value in ack_APIC_irq() instead of open-coded 0.
>
> Also, correct the EIO -> EOI typo in the constant name.
>
> Signed-off-by: Denis Mukhin <dmukhin@ford.com>
> ---
>  xen/arch/x86/include/asm/apic.h    | 3 +--
>  xen/arch/x86/include/asm/apicdef.h | 2 +-
>  2 files changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/xen/arch/x86/include/asm/apic.h b/xen/arch/x86/include/asm/apic.h
> index f30d57ad22c5..a4f6d2c26ce1 100644
> --- a/xen/arch/x86/include/asm/apic.h
> +++ b/xen/arch/x86/include/asm/apic.h
> @@ -155,8 +155,7 @@ void apic_wait_icr_idle(void);
>  
>  static inline void ack_APIC_irq(void)
>  {
> -	/* Docs say use 0 for future compatibility */
> -	apic_write(APIC_EOI, 0);
> +	apic_write(APIC_EOI, APIC_EOI_ACK);
>  }
>  
>  extern int get_maxlvt(void);
> diff --git a/xen/arch/x86/include/asm/apicdef.h b/xen/arch/x86/include/asm/apicdef.h
> index 112c1dc613a1..d3dc7b1d7643 100644
> --- a/xen/arch/x86/include/asm/apicdef.h
> +++ b/xen/arch/x86/include/asm/apicdef.h
> @@ -25,7 +25,7 @@
>  #define			APIC_ARBPRI_MASK	0xFF
>  #define		APIC_PROCPRI	0xA0
>  #define		APIC_EOI	0xB0
> -#define			APIC_EIO_ACK		0x0		/* Write this to the EOI register */
> +#define			APIC_EOI_ACK		0x0		/* Docs say use 0 for future compatibility */
>  #define		APIC_RRR	0xC0
>  #define		APIC_LDR	0xD0
>  #define			APIC_LDR_MASK		(0xFFu<<24)

Honestly, I'd prefer to delete this constant rather than to make use of
it.  The typo in the name shows it's not being used at all.

AMD have a feature called Selective EOI where you can write a vector in
and have it EOI something which isn't the currently in-service one.

~Andrew