Re: [Qemu-devel] [v5][PATCH 3/5] xen, gfx passthrough: support Intel IGD passthrough with VT-D

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Jun 25, 2014 at 10:17:19AM +0800, Tiejun Chen wrote:
> Some registers of Intel IGD are mapped in host bridge, so it needs to
> passthrough these registers of physical host bridge to guest because
> emulated host bridge in guest doesn't have these mappings.
> 
> The original patch is from Weidong Han <weidong.han@intel.com>
> 
> Signed-off-by: Yang Zhang <yang.z.zhang@Intel.com>
> Signed-off-by: Tiejun Chen <tiejun.chen@intel.com>
> Cc: Weidong Han <weidong.han@intel.com>
> ---
> v5:
> 
> * Don't pass vendor/device ids in igd_pci_read().
> * Add to support offset 0x44/0x48.
> 
> v4:
> 
> * Given that pci_create_pch() is called unconditionally, so we just return 0
>   even if its failed to check xen_has_gfx_passthru.
> * Remove one spurious change. 
> 
> v3:
> 
> * Improve comments to make that readable.
> 
> v2:
> 
> * To introduce is_igd_passthrough() to make sure we touch physical host bridge
>   only in IGD case.
> 
>  hw/xen/xen_pt.h          |   4 ++
>  hw/xen/xen_pt_graphics.c | 156 +++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 160 insertions(+)
> 
> diff --git a/hw/xen/xen_pt.h b/hw/xen/xen_pt.h
> index 4d3a18d..507165c 100644
> --- a/hw/xen/xen_pt.h
> +++ b/hw/xen/xen_pt.h
> @@ -302,5 +302,9 @@ extern int xen_has_gfx_passthru;
>  int xen_pt_register_vga_regions(XenHostPCIDevice *dev);
>  int xen_pt_unregister_vga_regions(XenHostPCIDevice *dev);
>  int xen_pt_setup_vga(XenHostPCIDevice *dev);
> +int pci_create_pch(PCIBus *bus);
> +void igd_pci_write(PCIDevice *pci_dev, uint32_t config_addr,
> +                   uint32_t val, int len);
> +uint32_t igd_pci_read(PCIDevice *pci_dev, uint32_t config_addr, int len);
>  
>  #endif /* !XEN_PT_H */
> diff --git a/hw/xen/xen_pt_graphics.c b/hw/xen/xen_pt_graphics.c
> index 974b7e9..f3fbfed 100644
> --- a/hw/xen/xen_pt_graphics.c
> +++ b/hw/xen/xen_pt_graphics.c
> @@ -4,6 +4,7 @@
>  #include "xen_pt.h"
>  #include "xen-host-pci-device.h"
>  #include "hw/xen/xen_backend.h"
> +#include "hw/pci/pci_bus.h"
>  
>  static int is_vga_passthrough(XenHostPCIDevice *dev)
>  {
> @@ -291,3 +292,158 @@ static int create_pseudo_pch_isa_bridge(PCIBus *bus, XenHostPCIDevice *hdev)
>      XEN_PT_LOG(dev, "The pseudo Intel PCH ISA bridge created.\n");
>      return 0;
>  }
> +
> +int pci_create_pch(PCIBus *bus)


Please prefix all xen specific non static functions
with xen_ or something like this.
pci_ is for pci core.

In fact it's a good idea to do this for static functions
as well, in case we add a conflicting function in
some header.

> +{
> +    XenHostPCIDevice hdev;
> +    int r = 0;
> +
> +    if (!xen_has_gfx_passthru) {
> +        return r;
> +    }
> +
> +    r = xen_host_pci_device_get(&hdev, 0, 0, 0x1f, 0);
> +    if (r) {
> +        XEN_PT_ERR(NULL, "Failed to find Intel PCH on host\n");
> +        goto err;
> +    }
> +
> +    if (hdev.vendor_id == PCI_VENDOR_ID_INTEL) {
> +        r = create_pseudo_pch_isa_bridge(bus, &hdev);
> +        if (r) {
> +            XEN_PT_ERR(NULL, "Failed to create PCH ISA bridge.\n");
> +            goto err;
> +        }
> +    }

Does it work on non intel?
It seems to return success.
Maybe you should just verify that vendor and device
ID have the expected values on the host, and
fail otherwise.

> +
> +    xen_host_pci_device_put(&hdev);
> +
> +err:
> +    return r;
> +}
> +
> +/*
> + * Currently we just pass this physical host bridge for IGD, 00:02.0.
> + *
> + * Here pci_dev is just that host bridge, so we have to get that real
> + * passthrough device by that given devfn to further confirm.
> + */


confirm what?
Comments like this need to document what function does.

Maybe

/* Can we support IGD passthrough for this device?
 * We require ... <XYZ - fill in here>
 */

> +static int is_igd_passthrough(PCIDevice *pci_dev)
> +{
> +    PCIDevice *f = pci_dev->bus->devices[PCI_DEVFN(2, 0)];
> +    if (pci_dev->bus->devices[PCI_DEVFN(2, 0)]) {
> +        XenPCIPassthroughState *s = DO_UPCAST(XenPCIPassthroughState, dev, f);
> +        return (is_vga_passthrough(&s->real_device)
> +                    && (s->real_device.vendor_id == PCI_VENDOR_ID_INTEL));
> +    } else {
> +        return 0;
> +    }
> +}
> +
> +void igd_pci_write(PCIDevice *pci_dev, uint32_t config_addr,
> +                   uint32_t val, int len)

Same here, xen_ everywhere please.

> +{
> +    XenHostPCIDevice dev;
> +    int r;
> +
> +    /* IGD read/write is through the host bridge.
> +     * ISA bridge is only for detect purpose. In i915 driver it will
> +     * probe ISA bridge to discover the IGD, see comment in i915_drv.c:
> +     * intel_detect_pch().

You mean in linux kernel I guess?

> +     */
> +
> +    assert(pci_dev->devfn == 0x00);
> +
> +    if (!is_igd_passthrough(pci_dev)) {
> +        goto write_default;
> +    }
> +
> +    /* Just work for the i915 driver. */
> +    switch (config_addr) {
> +    case 0x58:      /* PAVPC Offset */
> +        break;
> +    default:
> +        /* Just sets the emulated values. */
> +        goto write_default;
> +    }
> +
> +    /* Host write */
> +    r = xen_host_pci_device_get(&dev, 0, 0, 0, 0);
> +    if (r) {
> +        XEN_PT_ERR(pci_dev, "Can't get pci_dev_host_bridge\n");
> +        abort();
> +    }
> +
> +    r = xen_host_pci_set_block(&dev, config_addr, (uint8_t *)&val, len);
> +    if (r) {
> +        XEN_PT_ERR(pci_dev, "Can't get pci_dev_host_bridge\n");
> +        abort();
> +    }


Cleaner:

	if (config_addr == 0x58) {
	     /* Host write */
	     r = xen_host_pci_device_get(&dev, 0, 0, 0, 0);
	     if (r) {
	         XEN_PT_ERR(pci_dev, "Can't get pci_dev_host_bridge\n");
	         abort();
	     }
	 
	     r = xen_host_pci_set_block(&dev, config_addr, (uint8_t *)&val, len);
	     if (r) {
	         XEN_PT_ERR(pci_dev, "Can't get pci_dev_host_bridge\n");
	         abort();
	     }
	}

Note this does not work on e.g. BE.
The best way is really to make the register writeable in wmask.
Then
    pci_default_write_config(pci_dev, config_addr, val, len);
    if (range_covers_byte(addr, len, 0x58)) {
		....

	     r = xen_host_pci_set_block(&dev, config_addr,
		 pci_dev->config + config_addr, len);
    }





> +
> +    xen_host_pci_device_put(&dev);
> +
> +    return;
> +
> +write_default:
> +    pci_default_write_config(pci_dev, config_addr, val, len);
> +}
> +
> +uint32_t igd_pci_read(PCIDevice *pci_dev, uint32_t config_addr, int len)
> +{
> +    XenHostPCIDevice dev;
> +    uint32_t val;
> +    int r;
> +
> +    /* IGD read/write is through the host bridge.
> +     * ISA bridge is only for detect purpose. In i915 driver it will
> +     * probe ISA bridge to discover the IGD, see comment in i915_drv.c:
> +     * intel_detect_pch().
> +     */
> +    assert(pci_dev->devfn == 0x00);
> +
> +    if (!is_igd_passthrough(pci_dev)) {
> +        goto read_default;
> +    }
> +
> +    /* Just work for the i915 driver. */
> +    switch (config_addr) {
> +    case 0x08:        /* revision id */
> +    case 0x2c:        /* sybsystem vendor id */
> +    case 0x2e:        /* sybsystem id */

Since you set them to match host previously,
should be no need to override now.

> +    case 0x44:        /* MCHBAR I915 */
> +    case 0x48:        /* MCHBAR I965 */
> +    case 0x50:        /* SNB: processor graphics control register */
> +    case 0x52:        /* processor graphics control register */
> +    case 0xa0:        /* top of memory */
> +    case 0xb0:        /* ILK: BSM: should read from dev 2 offset 0x5c */
> +    case 0x58:        /* SNB: PAVPC Offset */
> +    case 0xa4:        /* SNB: graphics base of stolen memory */
> +    case 0xa8:        /* SNB: base of GTT stolen memory */

Move the actual code here.

> +        break;
> +    default:
> +        /* Just gets the emulated values. */

and here.

> +        goto read_default;
> +    }
> +
> +    /* Host read */
> +    r = xen_host_pci_device_get(&dev, 0, 0, 0, 0);
> +    if (r) {
> +        goto err_out;
> +    }
> +
> +    r = xen_host_pci_get_block(&dev, config_addr, (uint8_t *)&val, len);
> +    if (r) {
> +        goto err_out;
> +    }
> +
> +    xen_host_pci_device_put(&dev);
> +
> +    return val;
> +
> +read_default:
> +    return pci_default_read_config(pci_dev, config_addr, len);
> +
> +err_out:
> +    XEN_PT_ERR(pci_dev, "Can't get pci_dev_host_bridge\n");
> +    return -1;
> +}
> -- 
> 1.9.1