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

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

On 8/21/19 8:20 AM, Daniel Vetter wrote:
> On Wed, Aug 21, 2019 at 3:55 PM Ville Syrjälä
> <ville.syrjala@linux.intel.com> wrote:
>>
>> 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.
> 
> Yeah I think this is just more fallout from "no more fences in the hw".
> -Daniel
> 

Is anyone looking at implementing this (fence = 0 and reject tiled FBs) 
for TGL? I can pick it up if no one is.

Daniele

>>
>>> 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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>>> https://lists.freedesktop.org/mailman/listinfo/intel-gfx
>>
>> --
>> Ville Syrjälä
>> Intel
> 
> 
> 
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