[Intel-gfx] [RFC 2/2] drm/i915: Render decompression support for Gen9

[Konduru, Chandra]

> -----Original Message-----
> From: Daniel Stone [mailto:daniel at fooishbar.org]
> Sent: Wednesday, December 23, 2015 1:37 AM
> To: Kannan, Vandana
> Cc: intel-gfx; Konduru, Chandra; Murthy, Arun R
> Subject: Re: [Intel-gfx] [RFC 2/2] drm/i915: Render decompression support for
> Gen9
> 
> Hi Vandana,
> 
> On 23 December 2015 at 03:20, Kannan, Vandana
> <vandana.kannan at intel.com> wrote:
> > How does VT switch work in case of rotation, setting different pixel format,
> > etc?
> 
> Pixel format is a property of the framebuffer, not a per-plane
> property, so is unaffected. Rotation is generic, so there is specific
> code to handle it for fbdev etc.
> 
> But the real problem is that this is an Intel-specific property, and
> in order to get correct results, userspace must know about these
> specific properties in order to unset them. This means that you can't
> run generic userspace, and you can't run old userspace which predates
> these properties either. This seems like a total non-starter to me.
> 
> It would be much cleaner if there was a way to attach the render
> compression property to the framebuffer, e.g. by using the format
> modifiers which were specifically introduced to deal with compression
> and tiling.
> 
> Cheers,
> Daniel

Hi Daniel,
Plan is to handle compression property similar to rotation property. 
Don't see why that will be an issue. 

To address VT-switch concern, there will be a small code change 
resetting compression property in the VT-switch case - which may as well 
apply to other properties.

Please let us know if this is resolving your feedback.

By the way, for rotation in VT switch path (or any other property), 
there isn't code to reset to 0. The only place where reset is at  
"i915_driver_lastclose - clean up after all DRM clients have exited".

Thanks,
Chandra