Re: [PATCH 04/15] drm/i915: Flush the execlist ports if idle

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

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

> When doing a GPU reset, the CSB register will be trashed and we will
> lose any context-switch notifications that happened since the tasklet
> was disabled. If we find that all requests on this engine were
> completed, we want to make sure that the ELSP tracker is similarly empty
> so that we do not feed back in the completed requests upon recovering
> from the reset.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>

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

> ---
>  drivers/gpu/drm/i915/intel_lrc.c | 36 ++++++++++++++++++++++++++----------
>  1 file changed, 26 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index 3c83f2dd6798..ad61d1998fb7 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -1327,6 +1327,31 @@ static void reset_common_ring(struct intel_engine_cs *engine,
>  {
>  	struct execlist_port *port = engine->execlist_port;
>  	struct intel_context *ce;
> +	unsigned int n;
> +
> +	/*
> +	 * Catch up with any missed context-switch interrupts.
> +	 *
> +	 * Ideally we would just read the remaining CSB entries now that we
> +	 * know the gpu is idle. However, the CSB registers are sometimes^W
> +	 * often trashed across a GPU reset! Instead we have to rely on
> +	 * guessing the missed context-switch events by looking at what
> +	 * requests were completed.
> +	 */
> +	if (!request) {
> +		for (n = 0; n < ARRAY_SIZE(engine->execlist_port); n++)
> +			i915_gem_request_put(port_request(&port[n]));
> +		memset(engine->execlist_port, 0, sizeof(engine->execlist_port));
> +		return;
> +	}
> +
> +	if (request->ctx != port_request(port)->ctx) {
> +		i915_gem_request_put(port_request(port));
> +		port[0] = port[1];
> +		memset(&port[1], 0, sizeof(port[1]));
> +	}
> +
> +	GEM_BUG_ON(request->ctx != port_request(port)->ctx);
>  
>  	/* If the request was innocent, we leave the request in the ELSP
>  	 * and will try to replay it on restarting. The context image may
> @@ -1338,7 +1363,7 @@ static void reset_common_ring(struct intel_engine_cs *engine,
>  	 * and have to at least restore the RING register in the context
>  	 * image back to the expected values to skip over the guilty request.
>  	 */
> -	if (!request || request->fence.error != -EIO)
> +	if (request->fence.error != -EIO)
>  		return;
>  
>  	/* We want a simple context + ring to execute the breadcrumb update.
> @@ -1360,15 +1385,6 @@ static void reset_common_ring(struct intel_engine_cs *engine,
>  	request->ring->head = request->postfix;
>  	intel_ring_update_space(request->ring);
>  
> -	/* Catch up with any missed context-switch interrupts */
> -	if (request->ctx != port_request(port)->ctx) {
> -		i915_gem_request_put(port_request(port));
> -		port[0] = port[1];
> -		memset(&port[1], 0, sizeof(port[1]));
> -	}
> -
> -	GEM_BUG_ON(request->ctx != port_request(port)->ctx);
> -
>  	/* Reset WaIdleLiteRestore:bdw,skl as well */
>  	request->tail =
>  		intel_ring_wrap(request->ring,
> -- 
> 2.13.2
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