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

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Message-ID: <1869747233.4556840.1564996693878.JavaMail.zimbra@redhat.com>
Date:   Mon, 5 Aug 2019 05:18:13 -0400 (EDT)
From:   Frediano Ziglio <fziglio@...hat.com>
To:     Gerd Hoffmann <kraxel@...hat.com>
Cc:     dri-devel@...ts.freedesktop.org, David Airlie <airlied@...ux.ie>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:DRM DRIVER FOR QXL VIRTUAL GPU" 
        <virtualization@...ts.linux-foundation.org>,
        Daniel Vetter <daniel@...ll.ch>,
        "open list:DRM DRIVER FOR QXL VIRTUAL GPU" 
        <spice-devel@...ts.freedesktop.org>,
        Dave Airlie <airlied@...hat.com>
Subject: Re: [Spice-devel] [PATCH] drm/qxl: get vga ioports

> 
> 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@...hat.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