On Wed, Dec 19, 2012 at 12:53 AM, Jesse Barnes <jbarnes at virtuousgeek.org> wrote:
> On Wed, 19 Dec 2012 00:49:28 +0800
> "G.R." <firemeteor at 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.
>
I can add a comment here if the overall idea is acceptable to you.
But there is already a comment mentioning that the ISA bridge check is
for virtualization:
404 /*
405 * The reason to probe ISA bridge instead of Dev31:Fun0 is to
406 * make graphics device passthrough work easy for VMM, that only
407 * need to expose ISA bridge to let driver know the real hardware
408 * underneath. This is a requirement from virtualization team.
409 */
> Ack on the general idea though; I'd like us to be able to run under Xen
> without modification.
>
Stefano may be able to comment if it's feasible to achieve zero
modification in this case.
I believe this has something to do with getting rid of the PIIX3
device provided by qemu.
But generally I think it's very hard to achieve perfect emulation.
You can't always foresee what assumption a guest driver would make.
Maybe we need some compromise.
> Jesse
>
> --
> Jesse Barnes, Intel Open Source Technology Center
