Re: [PATCH v2] drm/i915: Restore inhibiting the load of the default context

[Mika Kuoppala <mika.kuoppala@linux.intel.com>]

Chris Wilson <chris@chris-wilson.co.uk> writes:

> Following a GPU reset, we may leave the context in a poorly defined
> state, and reloading from that context will leave the GPU flummoxed. For
> secondary contexts, this will lead to that context being banned - but
> currently it is also causing the default context to become banned,
> leading to turmoil in the shared state.
>
> This is a regression from
>
> commit 6702cf16e0ba8b0129f5aa1b6609d4e9c70bc13b [v4.1]
> Author: Ben Widawsky <benjamin.widawsky@intel.com>
> Date:   Mon Mar 16 16:00:58 2015 +0000
>
>     drm/i915: Initialize all contexts
>
> which quietly introduced the removal of the MI_RESTORE_INHIBIT on the
> default context.
>
> v2: Mark the global default context as uninitialized on GPU reset so
> that the context-local workarounds are reloaded upon re-enabling.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>

> Cc: Michel Thierry <michel.thierry@intel.com>
> Cc: Mika Kuoppala <mika.kuoppala@intel.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> ---
>  drivers/gpu/drm/i915/i915_gem_context.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
> index 43761c5bcaca..f024d5d2c746 100644
> --- a/drivers/gpu/drm/i915/i915_gem_context.c
> +++ b/drivers/gpu/drm/i915/i915_gem_context.c
> @@ -340,6 +340,10 @@ void i915_gem_context_reset(struct drm_device *dev)
>  			i915_gem_context_unreference(lctx);
>  			ring->last_context = NULL;
>  		}
> +
> +		/* Force the GPU state to be reinitialised on enabling */
> +		if (ring->default_context)
> +			ring->default_context->legacy_hw_ctx.initialized = false;
>  	}
>  }
>  
> @@ -708,7 +712,7 @@ static int do_switch(struct drm_i915_gem_request *req)
>  	if (ret)
>  		goto unpin_out;
>  
> -	if (!to->legacy_hw_ctx.initialized) {
> +	if (!to->legacy_hw_ctx.initialized || i915_gem_context_is_default(to)) {
>  		hw_flags |= MI_RESTORE_INHIBIT;
>  		/* NB: If we inhibit the restore, the context is not allowed to
>  		 * die because future work may end up depending on valid address
> -- 
> 2.6.2
>
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