Re: [PATCH 03/17] drm/i915: Allow the user to pass a context to any ring

[Chris Wilson <chris@chris-wilson.co.uk>]

On Mon, Aug 22, 2016 at 02:23:28PM +0300, Joonas Lahtinen wrote:
> On ma, 2016-08-22 at 09:03 +0100, Chris Wilson wrote:
> > With full-ppgtt, we want the user to have full control over their memory
> > layout, with a separate instance per context. Forcing them to use a
> > shared memory layout for !RCS not only duplicates the amount of work we
> > have to do, but also defeats the memory segregation on offer.
> > 
> > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> > ---
> >  drivers/gpu/drm/i915/i915_gem_execbuffer.c | 5 +----
> >  1 file changed, 1 insertion(+), 4 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> > index 8f9d5ad0cfd8..fb1a64738fb8 100644
> > --- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> > +++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> > @@ -1250,12 +1250,9 @@ static struct i915_gem_context *
> >  i915_gem_validate_context(struct drm_device *dev, struct drm_file *file,
> >  			  struct intel_engine_cs *engine, const u32 ctx_id)
> >  {
> > -	struct i915_gem_context *ctx = NULL;
> > +	struct i915_gem_context *ctx;
> >  	struct i915_ctx_hang_stats *hs;
> >  
> > -	if (engine->id != RCS && ctx_id != DEFAULT_CONTEXT_HANDLE)
> > -		return ERR_PTR(-EINVAL);
> > -
> 
> One would think this existed due to lack of testing or bugs in early
> hardware. Do we need to use IS_GEN or some other means of validation?

No.

This has nothing to do with the hardware logical state (that is found
within intel_context and only enabled where appropriate). The
i915_gem_context is the driver's segregation between clients. Not only
is t required for tracking clients independently (currently hangstats,
but the context would be the first place we start enforcing cgroups like
controls), but it is vital for clients who want to control their memory
layout without conflicts (with themselves and others).
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
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