Re: [PATCH 10/11] drm/i915: don't get/put runtime PM at the debugfs forcewake file

Daniel Vetter
2014-03-05T13:41:52Z

On Fri, Feb 21, 2014 at 01:52:27PM -0300, Paulo Zanoni wrote:
> From: Paulo Zanoni <paulo.r.zanoni@intel.com>
>
> Because gen6_gt_force_wake_{get,put} should already be responsible for
> getting/putting runtime PM.
>
> Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
> ---
> drivers/gpu/drm/i915/i915_debugfs.c | 2 --
> 1 file changed, 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index 62d0c0915..2ec7b05 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -3597,7 +3597,6 @@ static int i915_forcewake_open(struct inode *inode, struct file *file)
> if (INTEL_INFO(dev)->gen < 6)
> return 0;
>
> - intel_runtime_pm_get(dev_priv);
> gen6_gt_force_wake_get(dev_priv, FORCEWAKE_ALL);

I agree that doing the runtime get/put from within the forcewake get/put
gives us nice nesting. The with that is that we do the forcewake get/put
from within register I/O functions, which means it's not simple at all to
figure out where all runtime_pm_get is called, which can lead to some big
surprises around locking (since our resume functions do a _lot_ of work).

This is the reason why I've asked for the exception for the forcewake ->
runtime pm nesting. We could fix this properly by moving the forcewake
get/put out of the register read/write functions and sprinkle it
explicitly over the code, but that's a _lot_ more work.

For now I'll punt on this patch until convinced otherwise.
-Daniel

>
> return 0;
> @@ -3612,7 +3611,6 @@ static int i915_forcewake_release(struct inode *inode, struct file *file)
> return 0;
>
> gen6_gt_force_wake_put(dev_priv, FORCEWAKE_ALL);
> - intel_runtime_pm_put(dev_priv);
>
> return 0;
> }
> --
> 1.8.5.3
>
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--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch