[PATCH] drm/qxl: get vga ioports

[PATCH] drm/qxl: get vga ioports

[Gerd Hoffmann]

qxl has two modes: "native" (used by the drm driver) and "vga" (vga
compatibility mode, typically used for boot display and firmware
framebuffers).

Accessing any vga ioport will switch the qxl device into vga mode.
The qxl driver never does that, but other drivers accessing vga ports
can trigger that too and therefore disturb qxl operation.  So aquire
the legacy vga ioports from vgaarb to avoid that.

Reporducer: Boot kvm guest with both qxl and i915 vgpu, with qxl being
first in pci scan order.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
 drivers/gpu/drm/qxl/qxl_drv.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/qxl/qxl_drv.c b/drivers/gpu/drm/qxl/qxl_drv.c
index b57a37543613..8a2e86adc423 100644
--- a/drivers/gpu/drm/qxl/qxl_drv.c
+++ b/drivers/gpu/drm/qxl/qxl_drv.c
@@ -87,9 +87,15 @@ qxl_pci_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
 	if (ret)
 		goto disable_pci;
 
+	ret = vga_get_interruptible(pdev, VGA_RSRC_LEGACY_IO);
+	if (ret) {
+		DRM_ERROR("can't get legacy vga ports\n");
+		goto put_vga;
+	}
+
 	ret = qxl_device_init(qdev, &qxl_driver, pdev);
 	if (ret)
-		goto disable_pci;
+		goto put_vga;
 
 	ret = qxl_modeset_init(qdev);
 	if (ret)
@@ -109,6 +115,8 @@ qxl_pci_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
 	qxl_modeset_fini(qdev);
 unload:
 	qxl_device_fini(qdev);
+put_vga:
+	vga_put(pdev, VGA_RSRC_LEGACY_IO);
 disable_pci:
 	pci_disable_device(pdev);
 free_dev:
@@ -126,6 +134,7 @@ qxl_pci_remove(struct pci_dev *pdev)
 
 	qxl_modeset_fini(qdev);
 	qxl_device_fini(qdev);
+	vga_put(pdev, VGA_RSRC_LEGACY_IO);
 
 	dev->dev_private = NULL;
 	kfree(qdev);
-- 
2.18.1

Re: [Spice-devel] [PATCH] drm/qxl: get vga ioports

[Frediano Ziglio]

> 
> qxl has two modes: "native" (used by the drm driver) and "vga" (vga
> compatibility mode, typically used for boot display and firmware
> framebuffers).
> 
> Accessing any vga ioport will switch the qxl device into vga mode.
> The qxl driver never does that, but other drivers accessing vga ports
> can trigger that too and therefore disturb qxl operation.  So aquire
> the legacy vga ioports from vgaarb to avoid that.
> 
> Reporducer: Boot kvm guest with both qxl and i915 vgpu, with qxl being

typo: "Reporducer"

> first in pci scan order.
> 
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> ---
>  drivers/gpu/drm/qxl/qxl_drv.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/qxl/qxl_drv.c b/drivers/gpu/drm/qxl/qxl_drv.c
> index b57a37543613..8a2e86adc423 100644
> --- a/drivers/gpu/drm/qxl/qxl_drv.c
> +++ b/drivers/gpu/drm/qxl/qxl_drv.c
> @@ -87,9 +87,15 @@ qxl_pci_probe(struct pci_dev *pdev, const struct
> pci_device_id *ent)
>  	if (ret)
>  		goto disable_pci;
>  
> +	ret = vga_get_interruptible(pdev, VGA_RSRC_LEGACY_IO);
> +	if (ret) {
> +		DRM_ERROR("can't get legacy vga ports\n");
> +		goto put_vga;

I suppose that if this fails it's secondary so should continue.
What happen configuring 2 QXL devices?
Only a card should provide VGA registers in the system so
if any other card provide them QXL won't work.

> +	}
> +
>  	ret = qxl_device_init(qdev, &qxl_driver, pdev);
>  	if (ret)
> -		goto disable_pci;
> +		goto put_vga;
>  
>  	ret = qxl_modeset_init(qdev);
>  	if (ret)
> @@ -109,6 +115,8 @@ qxl_pci_probe(struct pci_dev *pdev, const struct
> pci_device_id *ent)
>  	qxl_modeset_fini(qdev);
>  unload:
>  	qxl_device_fini(qdev);
> +put_vga:
> +	vga_put(pdev, VGA_RSRC_LEGACY_IO);

What happen if you didn't get the I/O? Maybe it's safe to
just call vga_put and avoid adding an additional label here?

>  disable_pci:
>  	pci_disable_device(pdev);
>  free_dev:
> @@ -126,6 +134,7 @@ qxl_pci_remove(struct pci_dev *pdev)
>  
>  	qxl_modeset_fini(qdev);
>  	qxl_device_fini(qdev);
> +	vga_put(pdev, VGA_RSRC_LEGACY_IO);
>  
>  	dev->dev_private = NULL;
>  	kfree(qdev);

Frediano

Re: [Spice-devel] [PATCH] drm/qxl: get vga ioports

[Gerd Hoffmann]

  Hi,

> > +	ret = vga_get_interruptible(pdev, VGA_RSRC_LEGACY_IO);
> > +	if (ret) {
> > +		DRM_ERROR("can't get legacy vga ports\n");
> > +		goto put_vga;
> 
> I suppose that if this fails it's secondary so should continue.

Ah, right, there are secondary qxl cards (without the vga compat bits).
We should skip the call in that case (likewise for the cleanups).

> What happen configuring 2 QXL devices?
> Only a card should provide VGA registers in the system so
> if any other card provide them QXL won't work.

Well, with intel vgpu everything works fine with this patch.  Probably
i915 skips direct vga register access in case vga_get fails (because qxl
grabed them first).

In any case I'd prefer to fail qxl initialization over continuing
despite vga_get() having failed.  The failure mode is rather awkward:
qemu thinks the qxl card is in vga mode while the guest kernel thinks
qxl is in native mode.  Guest keeps queuing commands until the ring is
full while qemu never takes them out, so at some point the guest kernel
blocks forever in qxl_ring_push().

cheers,
  Gerd