[Intel-gfx] [RFC 34/60] drm/i915: introduce kernel blitter_context

[Lucas De Marchi]

On Fri, Jul 10, 2020 at 5:00 AM Matthew Auld <matthew.auld at intel.com> wrote:
>
> We may be without a context to perform various internal blitter
> operations, for example when performing object migration. Piggybacking
> off the kernel_context is probably a bad idea, since it has other uses.
>
> Signed-off-by: Matthew Auld <matthew.auld at intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> Cc: Abdiel Janulgue <abdiel.janulgue at linux.intel.com>
> ---
>  drivers/gpu/drm/i915/gt/intel_engine_cs.c    | 30 +++++++++++++++++---
>  drivers/gpu/drm/i915/gt/intel_engine_types.h |  1 +
>  2 files changed, 27 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_engine_cs.c b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> index dd1a42c4d344..1df94e82550f 100644
> --- a/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> +++ b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> @@ -792,6 +792,7 @@ create_kernel_context(struct intel_engine_cs *engine)
>         int err;
>
>         ce = intel_context_create(engine);
> +
>         if (IS_ERR(ce))
>                 return ce;
>
> @@ -845,16 +846,32 @@ static int engine_init_common(struct intel_engine_cs *engine)
>                 return PTR_ERR(ce);
>
>         ret = measure_breadcrumb_dw(ce);
> -       if (ret < 0)
> -               goto err_context;
> +       if (ret < 0) {
> +               intel_context_put(ce);

I think it's easier to follow the code if the error handling is in one
place. Since you have to put the context.
And since create_kernel_context() pins it, don't we have to
intel_context_unpin() like we are doing
in intel_engine_cleanup_common()?  Which would also mean to probably
factor out a `destroy_kernel_context()`
to always do it, and call from here and from intel_engine_cleanup_common().

Lucas De Marchi

> +               return ret;
> +       }
>
>         engine->emit_fini_breadcrumb_dw = ret;
>         engine->kernel_context = ce;
>
> +       /*
> +        * The blitter context is used to quickly memset or migrate objects
> +        * in local memory, so it has to always be available.
> +        */
> +       if (engine->class == COPY_ENGINE_CLASS) {
> +               ce = create_kernel_context(engine);
> +               if (IS_ERR(ce)) {
> +                       ret = PTR_ERR(ce);
> +                       goto err_kernel_context;
> +               }
> +
> +               engine->blitter_context = ce;
> +       }
> +
>         return 0;
>
> -err_context:
> -       intel_context_put(ce);
> +err_kernel_context:
> +       intel_context_put(engine->kernel_context);
>         return ret;
>  }
>
> @@ -910,6 +927,11 @@ void intel_engine_cleanup_common(struct intel_engine_cs *engine)
>         if (engine->default_state)
>                 fput(engine->default_state);
>
> +       if (engine->blitter_context) {
> +               intel_context_unpin(engine->blitter_context);
> +               intel_context_put(engine->blitter_context);
> +       }
> +
>         if (engine->kernel_context) {
>                 intel_context_unpin(engine->kernel_context);
>                 intel_context_put(engine->kernel_context);
> diff --git a/drivers/gpu/drm/i915/gt/intel_engine_types.h b/drivers/gpu/drm/i915/gt/intel_engine_types.h
> index 490af81bd6f3..3b2d9ed7670f 100644
> --- a/drivers/gpu/drm/i915/gt/intel_engine_types.h
> +++ b/drivers/gpu/drm/i915/gt/intel_engine_types.h
> @@ -342,6 +342,7 @@ struct intel_engine_cs {
>         struct llist_head barrier_tasks;
>
>         struct intel_context *kernel_context; /* pinned */
> +       struct intel_context *blitter_context; /* pinned; exists for BCS only */
>
>         intel_engine_mask_t saturated; /* submitting semaphores too late? */
>
> --
> 2.26.2
>
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-- 
Lucas De Marchi