[Intel-gfx] [PATCH] drm/i915: Take runtime pm reference on hangcheck_info

[Daniel Vetter]

On Thu, Feb 05, 2015 at 12:16:32PM +0200, Mika Kuoppala wrote:
> We read the coherent current seqno and actual head from ring.
> For hardware access we need to take runtime_pm reference, which brings in
> locking. As this debugfs entry is for debugging hangcheck behaviour,
> including locking problems, we need to be flexible on taking them.
> 
> Try to see if we get a lock and if so, get seqno and actual head
> from hardware. If we don't have exclusive access, get lazy coherent
> seqno and print token acthd for which the user can see that the
> seqno is of different nature.
> 
> Testcase: igt/pm_rpm/debugfs-read
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=88910
> Tested-by: Ding Heng <hengx.ding at intel.com>
> Signed-off-by: Mika Kuoppala <mika.kuoppala at intel.com>
> ---
>  drivers/gpu/drm/i915/i915_debugfs.c | 26 +++++++++++++++++++++++---
>  1 file changed, 23 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index 9af17fb..5a6b0e2 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -1223,8 +1223,11 @@ out:
>  static int i915_hangcheck_info(struct seq_file *m, void *unused)
>  {
>  	struct drm_info_node *node = m->private;
> -	struct drm_i915_private *dev_priv = to_i915(node->minor->dev);
> +	struct drm_device *dev = node->minor->dev;
> +	struct drm_i915_private *dev_priv = dev->dev_private;
>  	struct intel_engine_cs *ring;
> +	u64 acthd[I915_NUM_RINGS];
> +	u32 seqno[I915_NUM_RINGS];
>  	int i;
>  
>  	if (!i915.enable_hangcheck) {
> @@ -1232,6 +1235,23 @@ static int i915_hangcheck_info(struct seq_file *m, void *unused)
>  		return 0;
>  	}
>  
> +	if (mutex_trylock(&dev->struct_mutex)) {

Why do we need dev->struct_mutex here?
-Daniel

> +		intel_runtime_pm_get(dev_priv);
> +
> +		for_each_ring(ring, dev_priv, i) {
> +			seqno[i] = ring->get_seqno(ring, false);
> +			acthd[i] = intel_ring_get_active_head(ring);
> +		}
> +
> +		intel_runtime_pm_put(dev_priv);
> +		mutex_unlock(&dev->struct_mutex);
> +	} else {
> +		for_each_ring(ring, dev_priv, i) {
> +			seqno[i] = ring->get_seqno(ring, true);
> +			acthd[i] = -1;
> +		}
> +	}
> +
>  	if (delayed_work_pending(&dev_priv->gpu_error.hangcheck_work)) {
>  		seq_printf(m, "Hangcheck active, fires in %dms\n",
>  			   jiffies_to_msecs(dev_priv->gpu_error.hangcheck_work.timer.expires -
> @@ -1242,12 +1262,12 @@ static int i915_hangcheck_info(struct seq_file *m, void *unused)
>  	for_each_ring(ring, dev_priv, i) {
>  		seq_printf(m, "%s:\n", ring->name);
>  		seq_printf(m, "\tseqno = %x [current %x]\n",
> -			   ring->hangcheck.seqno, ring->get_seqno(ring, false));
> +			   ring->hangcheck.seqno, seqno[i]);
>  		seq_printf(m, "\taction = %d\n", ring->hangcheck.action);
>  		seq_printf(m, "\tscore = %d\n", ring->hangcheck.score);
>  		seq_printf(m, "\tACTHD = 0x%08llx [current 0x%08llx]\n",
>  			   (long long)ring->hangcheck.acthd,
> -			   (long long)intel_ring_get_active_head(ring));
> +			   (long long)acthd[i]);
>  		seq_printf(m, "\tmax ACTHD = 0x%08llx\n",
>  			   (long long)ring->hangcheck.max_acthd);
>  	}
> -- 
> 1.9.1
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch