RfC: vfio: add vgpu edid support?
Zhenyu Wang
zhenyuw at linux.intel.com
Mon Sep 10 09:37:09 UTC 2018
On 2018.09.07 16:05:15 +0200, Gerd Hoffmann wrote:
> Hi,
>
> I consider adding EDID support to qemu, for display configuration.
>
> qemu patches are here:
> https://git.kraxel.org/cgit/qemu/log/?h=sirius/edid
>
> linux kernel patches are here:
> https://git.kraxel.org/cgit/linux/log/?h=edid
>
> Current (experimental) patches have support for the stdvga and
> virtio-vga.
>
> I think it would be quite useful for vgpu too. Unlike emulated devices
> vgpu's do not have a paravirtual display configuration path, because the
> standard way to configure the display is to simply read the edid from
> the monitor.
>
> Intel has two hard-coded edid blobs for that (depending on vgpu type).
> Not sure how nvidia handles this, but probably simliar. With qemu
> passing a edid blob for the virtual display instead of using the
> hardcoded blob we could make the display configuration much more
> flexible.
>
> Ideally qemu would also be able to update the edid blob at any time, and
> the vgpu will notify the guest about it (probably by emulating a monitor
> hotplug event). The guest can react on qemu window resizing then and
> adapt automatically, simliar to how it works with qxl and virtio-gpu.
What's the frequency for those edid update during resizing? Looks it's
possible to bring hotplug storm that I'm not sure if all guest drivers
for gvt has proper handling.
>
> The guest and the vgpu should be able to handle "odd" non-standard
> display resolutions like this (coming from random window resizing):
>
> Detailed mode: Clock 106.620 MHz, 477 mm x 330 mm
> 1212 1515 1551 1636 hborder 0
> 840 844 848 869 vborder 0
> -hsync -vsync
> VertFreq: 74 Hz, HorFreq: 65171 Hz
>
Some odd timing might not be supported, e.g can't get a sane PLL setting
calculation for clock required. As gvt exposes a virtual display pipeline
following hw definition, so guest driver still depend on sane output, I
think that may just go wrong with arbitrary mode..
> +/**
> + * VFIO_DEVICE_GFX_EDID_SET - _IOW(VFIO_TYPE, VFIO_BASE + 18,
> + * struct vfio_device_gfx_edid_set)
> + *
> + * Set edid blob.
> + *
> + * Should trigger monitor hotplug emulation, to notifiy the guest os
> + * that the edid has changed.
> + *
> + */
> +struct vfio_device_gfx_edid_set {
> + __u32 argsz;
> + __u32 flags;
> + /* in */
> + __u8 edid[256];
> +};
> +
I assume you have defined return value for the set too right? In case
for driver can't handle or invalid edid blob, etc.
> +#define VFIO_DEVICE_GFX_EDID_SET _IO(VFIO_TYPE, VFIO_BASE + 18)
> +
> /* -------- API for Type1 VFIO IOMMU -------- */
>
> /**
> --
> 2.9.3
>
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