Re: [PATCH] Fix intel_detect_pch() to work in xen environment.

[Jesse Barnes <jbarnes@virtuousgeek.org>]

On Wed, 19 Dec 2012 00:49:28 +0800
"G.R." <firemeteor@users.sourceforge.net> wrote:

> Hi guys,
> 
> In XEN HVM guest, there is always an emulated PIIX3 ISA bridge on slot 01.0.
> This shadows the PCH ISA bridge on 1f.0 with the current
> intel_detect_pch() implementation.
> The issue can be easily solved by looping through all the ISA bridges
> until the first match is found, instead of just check against the
> first one.
> 
> Here I attach the patch I used locally. It's created on Torvalds's git.
> Looking forward to your comments.
> 
> Thanks,
> Timothy
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
> index 530db83..3f7e5fb 100644
> --- a/drivers/gpu/drm/i915/i915_drv.c
> +++ b/drivers/gpu/drm/i915/i915_drv.c
> @@ -408,9 +408,11 @@ void intel_detect_pch(struct drm_device *dev)
>          * underneath. This is a requirement from virtualization team.
>          */
>         pch = pci_get_class(PCI_CLASS_BRIDGE_ISA << 8, NULL);
> -       if (pch) {
> +       while (pch) {
> +               struct pci_dev * curr = pch;
>                 if (pch->vendor == PCI_VENDOR_ID_INTEL) {
>                         unsigned short id;
> +                       unsigned found = 1;
>                         id = pch->device & INTEL_PCH_DEVICE_ID_MASK;
>                         dev_priv->pch_id = id;
> 
> @@ -440,10 +442,20 @@ void intel_detect_pch(struct drm_device *dev)
>                                 dev_priv->num_pch_pll = 0;
>                                 DRM_DEBUG_KMS("Found LynxPoint LP PCH\n");
>                                 WARN_ON(!IS_HASWELL(dev));
> +                       } else {
> +                               found = 0;
> +                       }
> +                       if (found) {
> +                               BUG_ON(dev_priv->num_pch_pll > I915_NUM_PLLS);
> +                               pci_dev_put(pch);
> +                               break;
>                         }
> -                       BUG_ON(dev_priv->num_pch_pll > I915_NUM_PLLS);
>                 }
> -               pci_dev_put(pch);
> +               pch = pci_get_class(PCI_CLASS_BRIDGE_ISA << 8, curr);
> +               pci_dev_put(curr);
> +       }
> +       if (!pch) {
> +               DRM_DEBUG_KMS("No PCH found?\n");
>         }
>  }
> 

I'd like to see a comment about this being for Xen in here, and I
wonder if there are other places where we might have to worry about the
Xen implementation.  In that case, setting a flag in dev_priv when we
don't find the PCH where we expect would be a good idea too.

Ack on the general idea though; I'd like us to be able to run under Xen
without modification.

Jesse

-- 
Jesse Barnes, Intel Open Source Technology Center