Re: [Intel-gfx] [PATCH 14/46] drm/i915: Expose logical engine instance to user

[Daniel Vetter <daniel@ffwll.ch>]

On Mon, Aug 09, 2021 at 06:37:01PM +0000, Matthew Brost wrote:
> On Mon, Aug 09, 2021 at 04:30:06PM +0200, Daniel Vetter wrote:
> > On Tue, Aug 03, 2021 at 03:29:11PM -0700, Matthew Brost wrote:
> > > Expose logical engine instance to user via query engine info IOCTL. This
> > > is required for split-frame workloads as these needs to be placed on
> > > engines in a logically contiguous order. The logical mapping can change
> > > based on fusing. Rather than having user have knowledge of the fusing we
> > > simply just expose the logical mapping with the existing query engine
> > > info IOCTL.
> > > 
> > > Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> > > Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> > 
> > Uapi must have a link to the userspace MR/patch set using this, and to the
> > igt patch set validating it.
> > 
> 
> Have an IGT:
> https://patchwork.freedesktop.org/patch/447008/?series=93071&rev=1
> 
> Not sure when the media UMD is going to be updated upstream to use this.
> Does that mean I can't merge this until the media UMD is ready? Seems
> like it but isn't that a circular dependency? How can the media team
> develop for a new uAPI that isn't in the kernel yet?

Yes and no. Full explainer here:

https://dri.freedesktop.org/docs/drm/gpu/drm-uapi.html#open-source-userspace-requirements

In the drm subsystem this is pretty much the only rule where if you break
it the book will be thrown at you with extreme prejudice.

Also wrt circular: If the umd aren't set up to test their branches against
kernel branches they need to fix their stuff. I know that internally
that's not been done, and its a disaster, but in upstream there's no room
for excuses. Both kernel and userspace needs to be in branches until it's
ready for merging.

> For what it is worth the downstream release is already using this.

Yeah which is another problem, shipping new uapi in downstream before it's
in upstream is decidedly not great.
-Daniel

> 
> Matt
> 
> > Ideally in each patch, since it's way too hard to unfortunately find the
> > cover letter late on.
> > 
> > Jason even went as far as making this a hard requirement because he wasted
> > a bit too much time trying to find the userspace for new uapi:
> > 
> > https://lore.kernel.org/dri-devel/20210804185704.624883-1-jason@jlekstrand.net/
> > 
> > Cheers, Daniel
> > 
> > >---
> > >  drivers/gpu/drm/i915/i915_query.c | 2 ++
> > >  include/uapi/drm/i915_drm.h       | 8 +++++++-
> > >  2 files changed, 9 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/i915_query.c b/drivers/gpu/drm/i915/i915_query.c
> > > index e49da36c62fb..8a72923fbdba 100644
> > > --- a/drivers/gpu/drm/i915/i915_query.c
> > > +++ b/drivers/gpu/drm/i915/i915_query.c
> > > @@ -124,7 +124,9 @@ query_engine_info(struct drm_i915_private *i915,
> > >  	for_each_uabi_engine(engine, i915) {
> > >  		info.engine.engine_class = engine->uabi_class;
> > >  		info.engine.engine_instance = engine->uabi_instance;
> > > +		info.flags = I915_ENGINE_INFO_HAS_LOGICAL_INSTANCE;
> > >  		info.capabilities = engine->uabi_capabilities;
> > > +		info.logical_instance = ilog2(engine->logical_mask);
> > >  
> > >  		if (copy_to_user(info_ptr, &info, sizeof(info)))
> > >  			return -EFAULT;
> > > diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
> > > index 7f13d241417f..ef72e07fe08c 100644
> > > --- a/include/uapi/drm/i915_drm.h
> > > +++ b/include/uapi/drm/i915_drm.h
> > > @@ -2706,14 +2706,20 @@ struct drm_i915_engine_info {
> > >  
> > >  	/** @flags: Engine flags. */
> > >  	__u64 flags;
> > > +#define I915_ENGINE_INFO_HAS_LOGICAL_INSTANCE		(1 << 0)
> > >  
> > >  	/** @capabilities: Capabilities of this engine. */
> > >  	__u64 capabilities;
> > >  #define I915_VIDEO_CLASS_CAPABILITY_HEVC		(1 << 0)
> > >  #define I915_VIDEO_AND_ENHANCE_CLASS_CAPABILITY_SFC	(1 << 1)
> > >  
> > > +	/** @logical_instance: Logical instance of engine */
> > > +	__u16 logical_instance;
> > > +
> > >  	/** @rsvd1: Reserved fields. */
> > > -	__u64 rsvd1[4];
> > > +	__u16 rsvd1[3];
> > > +	/** @rsvd2: Reserved fields. */
> > > +	__u64 rsvd2[3];
> > >  };
> > >  
> > >  /**
> > > -- 
> > > 2.28.0
> > > 
> > 
> > -- 
> > Daniel Vetter
> > Software Engineer, Intel Corporation
> > http://blog.ffwll.ch

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch