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

[Eric Anholt]

Daniel Vetter <daniel at ffwll.ch> writes:

> On Wed, Nov 28, 2018 at 01:52:56PM -0800, Eric Anholt wrote:
>> Daniel Vetter <daniel at ffwll.ch> writes:
>> 
>> > On Tue, Nov 27, 2018 at 12:38:44PM -0800, Eric Anholt wrote:
>> >> Daniel Vetter <daniel at ffwll.ch> writes:
>> >> 
>> >> > On Mon, Nov 26, 2018 at 04:36:21PM -0800, Eric Anholt wrote:
>> >> >> Noralf Trønnes <noralf at 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).

FWIW, I really want shmem helpers for v3d.  The fault handling in
particular has magic I don't understand, and this is not my first fault
handler. :/
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