linux-kernel - Re: [PATCH 1/2] vfio: add edid api for display (vgpu) devices.

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Message-ID: <20180917085033.ttcs3cpznnf3wngd@sirius.home.kraxel.org>
Date:   Mon, 17 Sep 2018 10:50:33 +0200
From:   Gerd Hoffmann <kraxel@...hat.com>
To:     Zhenyu Wang <zhenyuw@...ux.intel.com>
Cc:     Alex Williamson <alex.williamson@...hat.com>,
        Kirti Wankhede <kwankhede@...dia.com>,
        intel-gvt-dev@...ts.freedesktop.org,
        open list <linux-kernel@...r.kernel.org>, kvm@...r.kernel.org
Subject: Re: [PATCH 1/2] vfio: add edid api for display (vgpu) devices.

> > +#define VFIO_DEVICE_INFO_CAP_EDID	1
> > +
> > +struct vfio_device_info_edid_cap {
> > +	struct vfio_info_cap_header header;
> > +	__u32   max_x;     /* Max display height (zero == no limit) */
> > +	__u32   max_y;     /* Max display height (zero == no limit) */
> > +};
> 
> As current virtual display for Intel vGPU is still emulating against real HW
> pipeline with same limitations, asked display developers that whether or not
> specific mode can work might still depend on current or future HW behavior.
> So could we add some hints on what kind of edid mode vfio device can operate?
> Some may support arbitrary modes, but some may only support standard modes.

What kind of restrictions do we have here?  Really to a fixed list of
standard modes?

Some testing (kaby lake) indicates y axis has no restrictions and x axis
gets rounded up to the next multiple of 8 pixels (32 bytes), maybe to
align scanlines with cachelines?

Oh, and btw:  Seems the resolution restriction (to 1024x768 for the
smallest vgpu type) seems to not be enforced.  Intentional?

cheers,
  Gerd