On Mon, Mar 14, 2011 at 9:03 AM, Marcus Lorentzon marcus.xm.lorentzon@stericsson.com wrote:
On 03/12/2011 04:59 PM, Rob Clark wrote:
On Sun, Dec 5, 2010 at 5:28 AM, Daniel Vetterdaniel@ffwll.ch wrote:
On Sat, Dec 04, 2010 at 04:34:22PM -0500, Alex Deucher wrote:
This doesn't seem that different from the graphics chips we support with kms. I don't think it would require much work to use KMS. One thing we considered, but never ended up implementing was a generic overlay API for KMS. Most PC hardware still has overlays, but we don't use them much any more on the desktop side. It may be worthwhile to design an appropriate API for them for these type of hardware.
Just fyi about a generic overlay api: I've looked a bit into this when doing the intel overlay support and I think adding special overlay crtcs that can be attached real crtcs gives a nice clean api. We could the reuse the existing framebuffer/pageflipping api to get the buffers to the overlay engine.
btw, has there been any further thought/discussion on this topic.. I've been experimenting with a drm driver interface on the OMAP SoC. It is working well now for framebuffer type usage (mode setting, virtual framebuffer spanning multiple diplays, and those types of xrandr things).. the next step that I've started thinking about is overlay (or underlay.. the z-order is flexible) support..
I was thinking in a similar direction (ie. a special, or maybe not so special, sort of crtc) and came across this thread, so I thought I'd resurrect the topic.
In our case, most of the CRTCs in our driver could be used either with (A)RGB buffers as a traditional framebuffer, or with a few different formats of YUV as video under/overlays. So if you had one display attached, you might only use one CRTC for traditional GUI/gfx layer, and the rest are available for video. If you had two displays, then you'd steal one of the video CRTCs and use it for the gfx layer on the second display. And so on.
We have similar HW and are also interested in finding some common ground for overlays in KMS. Just as you describe, we have no hard connection between a CRTC and output. Instead we only have overlays. Normal gfx use case is then of course one of these overlays dedicated to one display. And when adding video overlays, we also prefer YUV "underlays" with fullscreen ARGB gfx on top.
The problem with mapping this to the CRTCs in KMS today, is that there is no differentiation between framebuffer width/height and crt width/height. And of course YUV formats and fb position etc are missing.
One advantage of the set CRTC ioctl is that all information needed to switch mode is contained in one atomic set mode ioctl. So we have to think about if we want a new more advanced set crtc including overlay config. Or if we want to split mode setup into several requests. And then we must decide if multiple setup ioctls will need some type of "commit" to get the atomic mode switch we have today. For example I don't want to have to do a set_crtc enabling blending without overlay being setup. It should be just as glitch free as KMS is today.
Rough thinking:
- add some 'caps' to the CRTC to indicate whether it can handle YUV,
ARGB, scaling
- add an x/y offset relative to the encoder (as opposed to the
existing x/y offset relative to the framebuffer)
- add a z-order parameter
Exactly what I would like to have. Especially the caps for scaling, since we have one HW that can't do scaling.
Not sure about intel hw if it is supporting clip-rects.. if so, maybe need to add something about that. In our case we jut put the video behind the gfx layer and use the alpha channel in the gfx framebuffer to clip/blend rather than using clip-rects.
If this is common ground, I would like to have one clip rect per CRTC/overlay to enable framebuffers larger than overlay viewport. That makes it easier to reuse a large buffer for multiple overlays/framebuffers without having to stress memory management driver. But this is just a "nice to have" feature. Maybe this can be mapped to stride/start address mappings on HW without clip rect. But that will probably include alignment requirements on position and size.
Good point, I had overlooked that but we do have same requirement for cropping as well.. although in the crtc we already specify an x/y offset within the drm_framebuffer that the crtc is attached to.. so I guess if we have an input width/height (output is implied I guess by the encoder/connector) then we should be fine for cropping
Although in some cases top/left crop offset could be changing frame by frame (think use cases like zero-copy video stabilization or pan/scan) so might be nice to have a way to specify new x/y offset when flipping. I guess that would be an extension/change to existing page flip ioctl.
BR, -R
The real pain starts when we want format discovery from userspace with all the alignement/size/layout constrains. Add in tiling support and its almost impossible to do in a generic way. But also for kms userspace needs to know these constrains (implemented for generic use in libkms). I favor such an approach for overlays, too (if it ever happens) - i.e. a few helpers in libkms that allocate an appropriate buffer for a given format and size and returns the buffer, strides and offsets for the different planes.
hmm, I guess I know about the OMAP display subsystem, and it's overlay formats/capabilities.. but not enough about other hw to say anything intelligent here. But I guess even if we ignore the format of the data in the buffer, at least the APIs to setup/attach overlay CRTCs at various positions could maybe be something we can start with as a first step. At least standardizing this part seems like a good first step. But I'm definitely interested if someone has some ideas.
Yes, so we could try and find some common ground and add support for that. But still enable drivers to extend that with the features where we find no common ground. Just as GEM doesn't provide allocation ioctl, only free.
And in the end we have to see if the common ground is enough to actually build an application on. If not, there's not much use for a partial common API. Maybe that's why there's no overlay API in KMS tiday?
Maybe vendor libkms can be used to fill in the gaps?
/BR /Marcus