Re: [Qemu-devel] [PATCH v3 11/11] igd: move igd-passthrough-isa-bridge creation to machine init

From: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
To: Gerd Hoffmann <kraxel@redhat.com>
Cc: igvt-g@ml01.01.org, xen-devel@lists.xensource.com,
	Eduardo Habkost <ehabkost@redhat.com>,
	Stefano Stabellini <stefano.stabellini@eu.citrix.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	qemu-devel@nongnu.org, Cao jin <caoj.fnst@cn.fujitsu.com>,
	vfio-users@redhat.com, Paolo Bonzini <pbonzini@redhat.com>,
	Richard Henderson <rth@twiddle.net>
Subject: Re: [Qemu-devel] [PATCH v3 11/11] igd: move igd-passthrough-isa-bridge creation to machine init
Date: Wed, 6 Jan 2016 15:36:32 +0000	[thread overview]
Message-ID: <alpine.DEB.2.02.1601061534000.1756@kaball.uk.xensource.com> (raw)
In-Reply-To: <1451994098-6972-12-git-send-email-kraxel@redhat.com>

On Tue, 5 Jan 2016, Gerd Hoffmann wrote:
> This patch moves igd-passthrough-isa-bridge creation out of the xen
> passthrough code into machine init.  It is triggered by the
> igd-passthru=on machine option.  Advantages:
> 
>  * This works for on both xen and kvm.
>  * It is activated for the pc machine type only, q35 has a real
>    isa bridge on 1f.0 and must be handled differently.  The q35
>    plan is https://lkml.org/lkml/2015/11/26/183 (should land in
>    the next merge window, i.e. linux 4.5).
>  * If we don't need it any more some day (intel is busy removing
>    chipset dependencies from the guest driver) we have a single
>    machine switch to just turn off all igd passthru chipset
>    tweaks.
> 
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> ---
>  hw/i386/pc_piix.c |  6 ++++++
>  hw/xen/xen_pt.c   | 14 --------------
>  2 files changed, 6 insertions(+), 14 deletions(-)
> 
> diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
> index f36222e..2afbbd3 100644
> --- a/hw/i386/pc_piix.c
> +++ b/hw/i386/pc_piix.c
> @@ -281,6 +281,12 @@ static void pc_init1(MachineState *machine,
>      if (pcmc->pci_enabled) {
>          pc_pci_device_init(pci_bus);
>      }
> +
> +#ifdef CONFIG_LINUX
> +    if (machine->igd_gfx_passthru) {
> +        igd_passthrough_isa_bridge_create(pci_bus);
> +    }
> +#endif

One thing I don't like about this is that it is going to skip the checks
done in xen_pt_initfn. For example it is going to create the isa bridge,
even if there is going to be an error loading the vga bios or if the
device specified is not even an Intel graphic card.

>  }
>  
>  /* Looking for a pc_compat_2_4() function? It doesn't exist.
> diff --git a/hw/xen/xen_pt.c b/hw/xen/xen_pt.c
> index 18a7f72..5f626c9 100644
> --- a/hw/xen/xen_pt.c
> +++ b/hw/xen/xen_pt.c
> @@ -685,17 +685,6 @@ static const MemoryListener xen_pt_io_listener = {
>      .priority = 10,
>  };
>  
> -static void
> -xen_igd_passthrough_isa_bridge_create(XenPCIPassthroughState *s,
> -                                      XenHostPCIDevice *dev)
> -{
> -    uint16_t gpu_dev_id;
> -    PCIDevice *d = &s->dev;
> -
> -    gpu_dev_id = dev->device_id;
> -    igd_passthrough_isa_bridge_create(d->bus);
> -}
> -
>  /* destroy. */
>  static void xen_pt_destroy(PCIDevice *d) {
>  
> @@ -810,9 +799,6 @@ static int xen_pt_initfn(PCIDevice *d)
>              xen_host_pci_device_put(&s->real_device);
>              return -1;
>          }
> -
> -        /* Register ISA bridge for passthrough GFX. */
> -        xen_igd_passthrough_isa_bridge_create(s, &s->real_device);
>      }
>  
>      /* Handle real device's MMIO/PIO BARs */
> -- 
> 1.8.3.1
> 