On Wed, 16 Jan 2008 19:49:34 +0000 Keith Whitwell <[EMAIL PROTECTED]> wrote:
> Jerome Glisse wrote: > > On Wed, 2008-01-16 at 17:35 +0000, Keith Whitwell wrote: > >> Pretty much every buffer is potentially a render target, for instance > >> all texture buffers when generating mipmaps, etc. > >> > >> In the example above, different parts of individual buffers may be > >> rendered to with different pitches, etc, ie when targetting different > >> mipmaps. Intel hardware uses the same pitch for all mipmaps, but this > >> is not universal. > >> > >> Furthermore things like GL's pixel buffers may be used with different > >> pitches etc according to the user's whim. > >> > >> In general one of the nicest things about the current memory manager is > >> that it does *not* impose this type of thing on regular buffer > >> management. I've worked with systems that do and it can be very > >> burdensome. > >> > >> It's not like this presents a security issue to the system at large, so > >> the question then is why make it a kernel function? You just end up > >> running into the limitations you've encoded into the kernel in > >> generation n when you're trying to do the work for generation n+1. > >> > >> One motiviation for this sort of thing might be making allocation of > >> fenced memory regions easier (fenced in the sense used in Intel HW, > >> referring to tiled memory). I think that might be better handled > >> specially without encumbering the system as a whole with a fixed > >> interpretation of buffer layout. > >> > >> Is there a specific issue that this proposal is trying to address? > >> > >> Keith > > > > Well main motivation was for mode setting and command checking, > > for radeon a proper command checking will need to do a lot of, > > (width|pitch)*height*bpp + alignment against bo size checking. > > I do see render buffer object as a way of greatly simplify this. > > But i won't fight for it, i am well aware that current bo are > > really nice because it doesn't enforce a policy. > > > > I guess my main concern is more about how to ask to mode setting > > to program card to use this kind or this kind of layout for > > scan out buffer. > > Modesetting and scanout buffers are a different kettle of fish - it may > be reasonable to have more policy there than we currently do, and I > don't think that the negatives I'm worried about apply so much to this > area. > > It's quite reasonable to expect that *somebody* in the display stack may > have more information than the 3d client driver about the necessary > format, layout, etc of a scanout buffer, and that information would be > necessary in order to get eg. page flipping to work correctly. > > It *may* be that the memory manager/kernel module has a role to play in > this -- I don't really know one way or another. I guess the argument is > stronger when you're talking about cases where the drm module does > modesetting itself. > > It should be possible to put together a proposal in this area that > doesn't negatively affect the 3d driver's ability to use buffers as > rendertargets in new & innovative ways. I'm not sure what it would look > like exactly, but I'd be happy to evaluate it in the above terms. > > Keith > Well we did have some more discussion on irc about this and i think that having this informations for framebuffer is the only place where this is truely needed. We already have special interface for framebuffer so i guess we could work our way from there without impacting bo. For things other than framebuffer i think the main outcome of the discussion we had is that this kind of informations should be exchanged in user space btw program who cares. For instance in an X server this kind of informations would be exchanged throught dri2, so we might just have to limit bo sharing to a group of client behind a same master (i am thinking of Dave'smulti-master work here which might bring us the foundation for this). So xserver is a drm master and each xserver client is a drm child or dependant of this master and bo can only be shared through the master. And finaly checking bo size even if we need to do some computation like (width*height*bpp) won't kill the performance and will let the user use its buffer in whatever way it sees fit as long as it doesn't go beyond the size. Cheers, Jerome Glisse <[EMAIL PROTECTED]> ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ -- _______________________________________________ Dri-devel mailing list Dri-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/dri-devel
