Re: [PATCH 1/3] drm/etnaviv: submit support for in-fences

[Gustavo Padovan <gustavo@padovan.org>]

2017-03-16 Philipp Zabel <p.zabel@pengutronix.de>:

> Hi Gustavo,
> 
> On Mon, 2017-03-13 at 14:37 -0300, Gustavo Padovan wrote:
> [...]
> > I was thinking on some function that would iterate over all fences in
> > the fence_array and check their context. The if we find our own gpu
> > context in there we fail the submit.
> 
> Why would we have to fail if somebody feeds us our own fences? Wouldn't
> it be enough to just wait if there are foreign fences in the array?

You don't need to fail necessarily. In my mind I had the use case that
maybe some driver could deadlock waiting for his own fence. What you
do with the information that the array has it a fence with the driver's
context is entirely up to the driver to decide.

> 
> How about something like this:
> 
> ----------8<----------
> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gem_submit.c b/drivers/gpu/drm/etnaviv/etnaviv_gem_submit.c
> index 364fe50d020de..0b0bdaf4406d4 100644
> --- a/drivers/gpu/drm/etnaviv/etnaviv_gem_submit.c
> +++ b/drivers/gpu/drm/etnaviv/etnaviv_gem_submit.c
> @@ -296,6 +296,22 @@ static void submit_cleanup(struct etnaviv_gem_submit *submit)
>  	kfree(submit);
>  }
>  
> +static bool dma_fence_all_in_context(struct dma_fence *fence, u64 context)
> +{
> +	if (dma_fence_is_array(fence)) {
> +		struct dma_fence_array *array = to_dma_fence_array(fence);
> +		int i;
> +
> +		for (i = 0; i < array->num_fences; i++) {
> +			if (array->fences[i]->context != context)
> +				return false;
> +		}
> +		return true;
> +	}
> +
> +	return fence->context == context;
> +}

If we don't mind having fences with our own context, why should we check
them?

Gustavo
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