Re: [PATCH 2/4] drm/i915: fix rc6 initialization on Ironlake

From: Chris Wilson <chris@chris-wilson.co.uk>
To: Ben Widawsky <ben@bwidawsk.net>, intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH 2/4] drm/i915: fix rc6 initialization on Ironlake
Date: Sat, 19 Mar 2011 07:55:01 +0000	[thread overview]
Message-ID: <0d30dc$lgdgge@orsmga001.jf.intel.com> (raw)
In-Reply-To: <1300489968-8574-3-git-send-email-ben@bwidawsk.net>

On Fri, 18 Mar 2011 16:12:46 -0700, Ben Widawsky <ben@bwidawsk.net> wrote:
> There is a race condition between setting PWRCTXA and executing
> MI_SET_CONTEXT. PWRCTXA must not be set until a valid context has been
> written (or else the GPU could possible go into rc6, and return to an
> invalid context).
> 
> Reported-and-Tested-by: Gu Rui <chaos.proton@gmail.com>
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=28582
> Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
> ---
>  drivers/gpu/drm/i915/intel_display.c |   32 +++++++++++++++++++++++++++++---
>  1 files changed, 29 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 790af25..c1e9c30 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -6603,14 +6603,27 @@ static int ironlake_setup_rc6(struct drm_device *dev)
>  	return 0;
>  }
>  
> +static int ironlake_wait_set_context(struct drm_device *dev)
> +{
> +	struct drm_i915_private *dev_priv = dev->dev_private;
> +	struct intel_ring_buffer *ring = LP_RING(dev_priv);
> +	int ret = -EAGAIN;
> +
> +	ret = wait_for((I915_READ_HEAD(ring) == I915_READ_TAIL(ring)), 1000);
> +	if (ret && atomic_read(&dev_priv->mm.wedged)) {
> +		ret = -EIO;
> +	} else if (!ret) { /* head == tail */
> +		ret = 0;
> +	}
> +
> +	return ret;
> +}

Let's make this a more generic function because it does look useful.

static inline int intel_ring_wait_idle(struct intel_ring_buffer *ring)
{
	return intel_wait_ring_buffer(ring, ring->space - 8);
}

> +
>  void ironlake_enable_rc6(struct drm_device *dev)
>  {
>  	struct drm_i915_private *dev_priv = dev->dev_private;
>  	int ret;
>  
> -	/* rc6 disabled by default due to repeated reports of hanging during
> -	 * boot and resume.
> -	 */
>  	if (!i915_enable_rc6)
>  		return;
>  
> @@ -6640,6 +6653,19 @@ void ironlake_enable_rc6(struct drm_device *dev)
>  	OUT_RING(MI_FLUSH);
>  	ADVANCE_LP_RING();
>  
> +	/*
> +	 * Wait for the command parser to advance past MI_SET_CONTEXT. The HW
> +	 * does an implicit flush, combined with MI_FLUSH above, it should be
> +	 * safe to assume that renderctx is valid
> +	 */
> +	ret = ironlake_wait_set_context(dev);
> +	if (ret) {
> +		if (ret == -EAGAIN)
> +			DRM_ERROR("rc6 switch took too long, freeing the bo");

Just report the failure in all cases and avoid jargon (if possible)!

if (intel_ring_wait_idle(LP_RING(dev_priv))) {
	DRM_ERROR("failed to enable automatic power saving\n");
	return;
}

-- 
Chris Wilson, Intel Open Source Technology Centre