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Date: Wed, 16 Jan 2013 11:44:18 -0600
From: Scott Wood <scottwood@freescale.com>
Subject: Re: [PATCH] KVM: PPC: add paravirt idle loop for 64-bit book E
To: Stuart Yoder <stuart.yoder@freescale.com>
References: <1358356884-14216-1-git-send-email-stuart.yoder@freescale.com>
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 (from stuart.yoder@freescale.com on Wed Jan 16 11:21:24 2013)
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Cc: kvm-ppc@vger.kernel.org, linuxppc-dev@ozlabs.org, agraf@suse.de,
 kvm@vger.kernel.org, Stuart Yoder <stuart.yoder@freescale.com>
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On 01/16/2013 11:21:24 AM, Stuart Yoder wrote:
> From: Stuart Yoder <stuart.yoder@freescale.com>
>=20
> loop was derived from book3e_idle()
>=20
> Signed-off-by: Stuart Yoder <stuart.yoder@freescale.com>
> ---
>  arch/powerpc/kernel/epapr_hcalls.S |   63 =20
> ++++++++++++++++++++++++++++++++++++
>  1 file changed, 63 insertions(+)
>=20
> diff --git a/arch/powerpc/kernel/epapr_hcalls.S =20
> b/arch/powerpc/kernel/epapr_hcalls.S
> index 62c0dc2..6a46bfb 100644
> --- a/arch/powerpc/kernel/epapr_hcalls.S
> +++ b/arch/powerpc/kernel/epapr_hcalls.S
> @@ -17,6 +17,68 @@
>  #include <asm/asm-compat.h>
>  #include <asm/asm-offsets.h>
>=20
> +#ifdef CONFIG_PPC64
> +/* epapr_ev_idle() was derived from book3e_idle() */
> +_GLOBAL(epapr_ev_idle)
> +	/* Save LR for later */
> +	mflr	r0
> +	std	r0,16(r1)
> +
> +	/* Hard disable interrupts */
> +	wrteei	0
> +
> +	/* Now check if an interrupt came in while we were soft disabled
> +	 * since we may otherwise lose it (doorbells etc...).
> +	 */
> +	lbz	r3,PACAIRQHAPPENED(r13)
> +	cmpwi	cr0,r3,0
> +	bnelr
> +
> +	/* Now we are going to mark ourselves as soft and hard enabled =20
> in
> +	 * order to be able to take interrupts while asleep. We inform =20
> lockdep
> +	 * of that. We don't actually turn interrupts on just yet tho.
> +	 */
> +#ifdef CONFIG_TRACE_IRQFLAGS
> +	stdu    r1,-128(r1)
> +	bl	.trace_hardirqs_on
> +	addi    r1,r1,128
> +#endif
> +	li	r0,1
> +	stb	r0,PACASOFTIRQEN(r13)
> +=09
> +	/* Interrupts will make use return to LR, so get something we =20
> want
> +	 * in there
> +	 */
> +	bl	1f
> +
> +	/* And return (interrupts are on) */
> +	ld	r0,16(r1)
> +	mtlr	r0
> +	blr
> +
> +1:	/* Let's set the _TLF_NAPPING flag so interrupts make us return
> +	 * to the right spot
> +	*/
> +	CURRENT_THREAD_INFO(r11, r1)
> +	ld	r10,TI_LOCAL_FLAGS(r11)
> +	ori	r10,r10,_TLF_NAPPING
> +	std	r10,TI_LOCAL_FLAGS(r11)
> +
> +	/* We can now re-enable hard interrupts and go to sleep */
> +	wrteei	1
> +idle_loop:
> +	LOAD_REG_IMMEDIATE(r11, EV_HCALL_TOKEN(EV_IDLE))
> +
> +.global epapr_ev_idle_start
> +epapr_ev_idle_start:
> +	li	r3, -1
> +	nop
> +	nop
> +	nop
> +	b	idle_loop
> +

We should probably do this as an assembler macro, so we can have one =20
instance of it that gets instantiated for both "wait" and "ev_idle".

-Scott=