Re: [PATCH 3/3] drm: omapdrm: Do no allocate non-scanout GEMs through DMM/TILER

[Tomi Valkeinen]

On 30/08/2022 21:08, Ivaylo Dimitrov wrote:

> > >          flags &= ~OMAP_BO_TILED_MASK;
> > >          flags |= 0x00000008;
> > >          flags |= OMAP_BO_WC;
> > >
> > >          bo = omap_bo_new(dev, size, flags);
> > >
> > > As you can see we use 0x00000008 (OMAP_BO_MEM_CONTIG) unconditionally.
> > > This was a hack added since even non-scanout buffers sometimes need
> > > to be contiguous (video decoder surfaces), but we had no way back
>
> Hmm, why would video decoder need linear memory? No MMU?

Not sure about this case, but many/most IPs don't have MMU. E.g. CSI-2 
or parallel capture.

> > > If you tell me what the code should look like, I can rebuild the
> > > lib and post a copy.
> > >
> > > Long term, I'd like to start using DMA-BUF Heaps for CMA memory
> > > allocations in gralloc and elsewhere, then drop out the DMM/TILER
> > > support from OMAPDRM, since it never really belonged there in
> > > the first place (being a IOMMU unrelated to the display/GPU).
>
> Umm, how will we rotate scanout buffers then?

Didn't we discuss this earlier in this thread. Or some other thread. 
Related to VRFB... I'm not sure =).

Anyway, neither VRFB nor DMM/TILER are part of the DSS. They're part of 
the memory subsystem. They can be used without DSS being in the setup. 
Thus the code for VRFB and DMM/TILER should not be in the DSS driver.

The DSS driver should still, of course, support DMM/TILER (and maybe 
VRFB some day) in the "use" sense, i.e. so that DSS can use the 
DMM/TILER provided from another driver.

But how exactly that's to be implemented, I don't know.

 Tomi