[Intel-gfx] [PATCH v3] drm/i915/guc: Make wq_lock irq-safe

[Michal Wajdeczko]

On Tue, Feb 28, 2017 at 09:28:10AM +0000, Chris Wilson wrote:
> Following the use of dma_fence_signal() from within our interrupt
> handler, we need to make guc->wq_lock also irq-safe. This was done
> previously as part of the guc scheduler patch (which also started
> mixing our fences with the interrupt handler), but is now required to
> fix the current guc submission backend.
> 
> v3: Use cmpxchg for the solitary adjustments of guc->wq_rsvd
> 
> Fixes: 67b807a89230 ("drm/i915: Delay disabling the user interrupt for breadcrumbs")
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
> ---
>  drivers/gpu/drm/i915/i915_guc_submission.c | 25 +++++++++++++++++--------
>  1 file changed, 17 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_guc_submission.c b/drivers/gpu/drm/i915/i915_guc_submission.c
> index beec88a30347..4a5cee16f901 100644
> --- a/drivers/gpu/drm/i915/i915_guc_submission.c
> +++ b/drivers/gpu/drm/i915/i915_guc_submission.c
> @@ -348,7 +348,7 @@ int i915_guc_wq_reserve(struct drm_i915_gem_request *request)
>  	u32 freespace;
>  	int ret;
>  
> -	spin_lock(&client->wq_lock);
> +	spin_lock_irq(&client->wq_lock);
>  	freespace = CIRC_SPACE(client->wq_tail, desc->head, client->wq_size);
>  	freespace -= client->wq_rsvd;
>  	if (likely(freespace >= wqi_size)) {
> @@ -358,21 +358,28 @@ int i915_guc_wq_reserve(struct drm_i915_gem_request *request)
>  		client->no_wq_space++;
>  		ret = -EAGAIN;
>  	}
> -	spin_unlock(&client->wq_lock);
> +	spin_unlock_irq(&client->wq_lock);
>  
>  	return ret;
>  }
>  
> +static void guc_wq_add_reserved(struct i915_guc_client *client, int delta)

Hmm, as delta can be negative, "add" verb maybe little misleading. What about "update" ?

Also, as in parallel there is ongoing cleanup effort, can we rename this function a bit
to match subject/verb pattern?

	static void guc_client_update_wq_reserved(struct i915_guc_client *client, int delta)

> +{
> +	unsigned int old, new;
> +
> +	do {
> +		old = client->wq_rsvd;
> +		new = old + delta;
> +	} while (cmpxchg(&client->wq_rsvd, old, new) != old);
> +}
> +
>  void i915_guc_wq_unreserve(struct drm_i915_gem_request *request)
>  {
> -	const size_t wqi_size = sizeof(struct guc_wq_item);
> +	const int wqi_size = sizeof(struct guc_wq_item);
>  	struct i915_guc_client *client = request->i915->guc.execbuf_client;
>  
>  	GEM_BUG_ON(READ_ONCE(client->wq_rsvd) < wqi_size);
> -
> -	spin_lock(&client->wq_lock);
> -	client->wq_rsvd -= wqi_size;
> -	spin_unlock(&client->wq_lock);
> +	guc_wq_add_reserved(client, -wqi_size);
>  }
>  
>  /* Construct a Work Item and append it to the GuC's Work Queue */
> @@ -951,10 +958,12 @@ int i915_guc_submission_enable(struct drm_i915_private *dev_priv)
>  		engine->schedule = NULL;
>  
>  		/* Replay the current set of previously submitted requests */
> +		spin_lock_irq(&engine->timeline->lock);
>  		list_for_each_entry(rq, &engine->timeline->requests, link) {
> -			client->wq_rsvd += sizeof(struct guc_wq_item);
> +			guc_wq_add_reserved(client, sizeof(struct guc_wq_item));

To be consistent with "unreserve" case, maybe we should define and then use wqi_size?

	const int wqi_size = sizeof(struct guc_wq_item);


>  			__i915_guc_submit(rq);
>  		}
> +		spin_unlock_irq(&engine->timeline->lock);
>  	}
>  
>  	return 0;


As I was using similar patch for fixing spin_locks on my local tree, 

Reviewed-by: Michal Wajdeczko <michal.wajdeczko at intel.com>

-Michal