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From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Date: Sat, 09 Sep 2017 17:39:10 +1000
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Subject: Re: [Qemu-devel] [RFC PATCH 16/26] ppc/xive: notify CPU when
 interrupt priority is more privileged
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To: =?ISO-8859-1?Q?C=E9dric?= Le Goater <clg@kaod.org>, David Gibson <david@gibson.dropbear.id.au>
Cc: qemu-ppc@nongnu.org, qemu-devel@nongnu.org

On Wed, 2017-07-05 at 19:13 +0200, C=C3=A9dric Le Goater wrote:
> Signed-off-by: C=C3=A9dric Le Goater <clg@kaod.org>
> ---
>  hw/intc/xive.c | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
>=20
> diff --git a/hw/intc/xive.c b/hw/intc/xive.c
> index c3c1e9c9db2d..cda1fa18e44d 100644
> --- a/hw/intc/xive.c
> +++ b/hw/intc/xive.c
> @@ -53,6 +53,21 @@ static uint64_t xive_icp_accept(XiveICPState *xicp)
>      return (nsr << 8) | xicp->tima_os[TM_CPPR];
>  }
> =20
> +static uint8_t ipb_to_pipr(uint8_t ibp)
> +{
> +    return ibp ? clz32((uint32_t)ibp << 24) : 0xff;
> +}

The PIPR needs to be updated also on accept etc... anything that change
IPBs or CPPR really.

Also I just learned something from the designers: The IPIR is clamped
to CPPR.

So basically the value in the PIPR is:

	v =3D leftmost_bit_of(ipb) (or 0xff);
	pipr =3D v < cppr ? v : cppr;

which means it's never actually 0xff ... surprise !

That also means I need to fix my implementation of H_IPOLL in KVM.

> +static void xive_icp_notify(XiveICPState *xicp)
> +{
> +    xicp->tima_os[TM_PIPR] =3D ipb_to_pipr(xicp->tima_os[TM_IPB]);
> +
> +    if (xicp->tima_os[TM_PIPR] < xicp->tima_os[TM_CPPR]) {
> +        xicp->tima_os[TM_NSR] |=3D TM_QW1_NSR_EO;
> +        qemu_irq_raise(ICP(xicp)->output);
> +    }
> +}
> +
>  static void xive_icp_set_cppr(XiveICPState *xicp, uint8_t cppr)
>  {
>      if (cppr > XIVE_PRIORITY_MAX) {
> @@ -60,6 +75,10 @@ static void xive_icp_set_cppr(XiveICPState *xicp, ui=
nt8_t cppr)
>      }
> =20
>      xicp->tima_os[TM_CPPR] =3D cppr;
> +
> +    /* CPPR has changed, inform the ICP which might raise an
> +     * exception */
> +    xive_icp_notify(xicp);
>  }
> =20
>  /*
> @@ -339,6 +358,8 @@ static void xive_icp_irq(XiveICSState *xs, int lisn=
)
>      } else {
>          qemu_log_mask(LOG_UNIMP, "XIVE: w7 format1 not implemented\n")=
;
>      }
> +
> +    xive_icp_notify(xicp);
>  }
> =20
>  /*