Re: [PATCH] drm/i915: disable set/get_tiling ioctl on gen12+

[Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>]

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? 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@intel.com>
> Cc: Stuart Summers <stuart.summers@intel.com>
> Cc: Matthew Auld <matthew.auld@intel.com>
> Cc: Kenneth Graunke <kenneth@whitecape.org>
> Cc: Jason Ekstrand <jason@jlekstrand.net>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Lucas De Marchi <lucas.demarchi@intel.com>
> Signed-off-by: Daniel Vetter <daniel.vetter@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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