Re: [Intel-gfx] [PATCH v5 4/5] drm: Add library for shmem backed GEM objects

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Nov 28, 2018 at 01:52:56PM -0800, Eric Anholt wrote:
> Daniel Vetter <daniel@ffwll.ch> writes:
> 
> > On Tue, Nov 27, 2018 at 12:38:44PM -0800, Eric Anholt wrote:
> >> Daniel Vetter <daniel@ffwll.ch> writes:
> >> 
> >> > On Mon, Nov 26, 2018 at 04:36:21PM -0800, Eric Anholt wrote:
> >> >> Noralf Trønnes <noralf@tronnes.org> writes:
> >> >> > +static void drm_gem_shmem_vm_close(struct vm_area_struct *vma)
> >> >> > +{
> >> >> > +	struct drm_gem_object *obj = vma->vm_private_data;
> >> >> > +	struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
> >> >> > +
> >> >> > +	drm_gem_shmem_put_pages(shmem);
> >> >> > +	drm_gem_vm_close(vma);
> >> >> > +}
> >> >> > +
> >> >> > +const struct vm_operations_struct drm_gem_shmem_vm_ops = {
> >> >> > +	.fault = drm_gem_shmem_fault,
> >> >> > +	.open = drm_gem_vm_open,
> >> >> > +	.close = drm_gem_shmem_vm_close,
> >> >> > +};
> >> >> > +EXPORT_SYMBOL_GPL(drm_gem_shmem_vm_ops);
> >> >> 
> >> >> I just saw a warning from drm_gem_shmem_put_pages() for
> >> >> !shmem->pages_use_count -- I think drm_gem_vm_open() needs to
> >> >> drm_gem_shmem_get_pages().
> >> >
> >> > Yeah we need a drm_gem_shmem_vm_open here.
> >> 
> >> Adding one of those fixed my refcounting issues, so I've sent out a v6
> >> with it.
> >
> > Just realized that I've reviewed this patch already, spotted that vma
> > management issue there too. Plus a pile of other things. From reading that
> > other thread discussion with Noralf concluded with "not yet ready for
> > prime time" unfortunately :-/
> 
> I saw stuff about how it wasn't usable for SPI because SPI does weird
> things with DMA mapping.  Was there something else?

Looking through that mail it was a bunch of comments to improve the
kerneldoc. Plus a note that buffer sharing/mmap is going to be all
incoherent and horrible (but I guess for vkms we don't care that much).
I'm just kinda vary of generic buffer handling that turns out to not be
actually all that useful. We have lots of deadends and kinda-midlayers in
this area already (but this one here definitely smells plenty better than
lots of older ones).
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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