[Intel-gfx] [PATCH] drm/i915: disable set/get_tiling ioctl on gen12+

[Ville Syrjälä]

On Tue, Aug 20, 2019 at 01:57:44PM -0700, Daniele Ceraolo Spurio wrote:
> 
> 
> On 8/20/19 12:54 PM, Daniel Vetter wrote:
> > The cpu (de)tiler hw is gone, this stopped being useful. Plus it never
> > supported any of the fancy new tiling formats, which means userspace
> > also stopped using the magic side-channel this provides.
> > 
> > This would totally break a lot of the igts, but they're already broken
> > for the same reasons as userspace on gen12 would be.
> > 
> > v2: Look at ggtt->num_fences instead, that also avoids the need for a
> > comment (Chris). This also means that gen12 support really needs to
> > make sure num_fences is set to 0. There is a patch for that, but it
> > checks for HAS_MAPPABLE_APERTURE, which I'm not sure is the right
> > thing really. Adding relevant people.
> > 
> 
> We'd obviously need to make that setting for all gen12+, because TGL 
> does have mappable aperture.
> 
> Apart from the tiling ioctl, the only place I see where we set tiling is 
> intel_alloc_initial_plane_obj(), can the users of that object handle the 
> lack of fences gracefully?

Gen4+ display engine has its own tiling controls and doesn't care about
fences. So we should be able to leave the obj tiling set to NONE.

Hmm. Actually I think we should reject tiled framebuffers in the BIOS
fb takeover because fbdev needs a linear view for the memory. No can
do without the fence.

> When I wrote the num_fences=0 patch I was 
> expecting display to be unavailable, so I didn't really look at that 
> part of the code.
> 
> It'd also be nice to be more explicit with fencing since we seem to 
> often call i915_vma_pin_iomap, which implicitly applies a fence if 
> needed, on objects that can't be tiled or have had a fence assigned a 
> few lines before. This is more a nice to have tough, possibly together 
> with a split of the "mappable" and "fenceable" attributes of the vma.
> 
> Daniele
> 
> > Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
> > Cc: Stuart Summers <stuart.summers at intel.com>
> > Cc: Matthew Auld <matthew.auld at intel.com>
> > Cc: Kenneth Graunke <kenneth at whitecape.org>
> > Cc: Jason Ekstrand <jason at jlekstrand.net>
> > Cc: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Lucas De Marchi <lucas.demarchi at intel.com>
> > Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
> > ---
> >   drivers/gpu/drm/i915/gem/i915_gem_tiling.c | 7 +++++++
> >   1 file changed, 7 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_tiling.c b/drivers/gpu/drm/i915/gem/i915_gem_tiling.c
> > index ca0c2f451742..e5d1ae8d4dba 100644
> > --- a/drivers/gpu/drm/i915/gem/i915_gem_tiling.c
> > +++ b/drivers/gpu/drm/i915/gem/i915_gem_tiling.c
> > @@ -313,10 +313,14 @@ int
> >   i915_gem_set_tiling_ioctl(struct drm_device *dev, void *data,
> >   			  struct drm_file *file)
> >   {
> > +	struct drm_i915_private *dev_priv = to_i915(dev);
> >   	struct drm_i915_gem_set_tiling *args = data;
> >   	struct drm_i915_gem_object *obj;
> >   	int err;
> >   
> > +	if (!dev_priv->ggtt.num_fences)
> > +		return -EOPNOTSUPP;
> > +
> >   	obj = i915_gem_object_lookup(file, args->handle);
> >   	if (!obj)
> >   		return -ENOENT;
> > @@ -402,6 +406,9 @@ i915_gem_get_tiling_ioctl(struct drm_device *dev, void *data,
> >   	struct drm_i915_gem_object *obj;
> >   	int err = -ENOENT;
> >   
> > +	if (!dev_priv->ggtt.num_fences)
> > +		return -EOPNOTSUPP;
> > +
> >   	rcu_read_lock();
> >   	obj = i915_gem_object_lookup_rcu(file, args->handle);
> >   	if (obj) {
> > 
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-- 
Ville Syrjälä
Intel