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From: Jani Nikula <jani.nikula@linux.intel.com>
To: intel-gfx@lists.freedesktop.org
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>, Ben Widawsky <ben@bwidawsk.net>
Subject: Re: [PATCH 2/3] drm/i915: Change forcewake timeout to 2ms
Date: Mon, 27 Aug 2012 09:59:49 +0300	[thread overview]
Message-ID: <87zk5gakgq.fsf@intel.com> (raw)
In-Reply-To: <1345836671-1180-3-git-send-email-ben@bwidawsk.net>

On Fri, 24 Aug 2012, Ben Widawsky <ben@bwidawsk.net> wrote:
> A designer familiar with the hardware has stated that the forcewake
> timeout can theoretically be as high as a little over 1ms. Therefore we
> modify our code to use 2ms (appropriate fudge and because we don't want
> to round down).
>
> Hopefully this can't prevent spurious timeouts.
>
> Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
> ---
>  drivers/gpu/drm/i915/intel_pm.c | 22 +++++++++++-----------
>  1 file changed, 11 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index f42c142..2a8468d 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -31,7 +31,7 @@
>  #include "../../../platform/x86/intel_ips.h"
>  #include <linux/module.h>
>  
> -#define FORCEWAKE_ACK_TIMEOUT_US 500
> +#define FORCEWAKE_ACK_TIMEOUT_MS 2
>  
>  /* FBC, or Frame Buffer Compression, is a technique employed to compress the
>   * framebuffer contents in-memory, aiming at reducing the required bandwidth
> @@ -3970,15 +3970,15 @@ static void __gen6_gt_force_wake_get(struct drm_i915_private *dev_priv)
>  	else
>  		forcewake_ack = FORCEWAKE_ACK;
>  
> -	if (wait_for_atomic_us((I915_READ_NOTRACE(forcewake_ack) & 1) == 0,
> -			       FORCEWAKE_ACK_TIMEOUT_US))
> +	if (wait_for_atomic((I915_READ_NOTRACE(forcewake_ack) & 1) == 0,
> +			    FORCEWAKE_ACK_TIMEOUT_MS))

Superficially this looks okay, but the implementation of
wait_for_atomic() not so. As a surprise, this change drops cpu_relax()
from the busy loop, even thought the timeout is potentially much longer.

The quick fix here would be to just use 2000 us with
wait_for_atomic_us(), but we should do something about wait_for_atomic()
too. Luckily it's only ever used at one place.

BR,
Jani.


>  		DRM_ERROR("Force wake wait timed out\n");
>  
>  	I915_WRITE_NOTRACE(FORCEWAKE, 1);
>  	POSTING_READ(FORCEWAKE);
>  
> -	if (wait_for_atomic_us((I915_READ_NOTRACE(forcewake_ack) & 1),
> -			       FORCEWAKE_ACK_TIMEOUT_US))
> +	if (wait_for_atomic((I915_READ_NOTRACE(forcewake_ack) & 1),
> +			    FORCEWAKE_ACK_TIMEOUT_MS))
>  		DRM_ERROR("Force wake wait timed out\n");
>  
>  	__gen6_gt_wait_for_thread_c0(dev_priv);
> @@ -3993,15 +3993,15 @@ static void __gen6_gt_force_wake_mt_get(struct drm_i915_private *dev_priv)
>  	else
>  		forcewake_ack = FORCEWAKE_MT_ACK;
>  
> -	if (wait_for_atomic_us((I915_READ_NOTRACE(forcewake_ack) & 1) == 0,
> -			       FORCEWAKE_ACK_TIMEOUT_US))
> +	if (wait_for_atomic((I915_READ_NOTRACE(forcewake_ack) & 1) == 0,
> +			    FORCEWAKE_ACK_TIMEOUT_MS))
>  		DRM_ERROR("Force wake wait timed out\n");
>  
>  	I915_WRITE_NOTRACE(FORCEWAKE_MT, _MASKED_BIT_ENABLE(1));
>  	POSTING_READ(FORCEWAKE_MT);
>  
> -	if (wait_for_atomic_us((I915_READ_NOTRACE(forcewake_ack) & 1),
> -			       FORCEWAKE_ACK_TIMEOUT_US))
> +	if (wait_for_atomic((I915_READ_NOTRACE(forcewake_ack) & 1),
> +			    FORCEWAKE_ACK_TIMEOUT_MS))
>  		DRM_ERROR("Force wake wait timed out\n");
>  
>  	__gen6_gt_wait_for_thread_c0(dev_priv);
> @@ -4088,8 +4088,8 @@ static void vlv_force_wake_get(struct drm_i915_private *dev_priv)
>  	I915_WRITE_NOTRACE(FORCEWAKE_VLV, 0xffffffff);
>  	POSTING_READ(FORCEWAKE_VLV);
>  
> -	if (wait_for_atomic_us((I915_READ_NOTRACE(FORCEWAKE_ACK_VLV) & 1),
> -			       FORCEWAKE_ACK_TIMEOUT_US))
> +	if (wait_for_atomic((I915_READ_NOTRACE(FORCEWAKE_ACK_VLV) & 1),
> +			    FORCEWAKE_ACK_TIMEOUT_MS))
>  		DRM_ERROR("Force wake wait timed out\n");
>  
>  	__gen6_gt_wait_for_thread_c0(dev_priv);
> -- 
> 1.7.12
>
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx

  reply	other threads:[~2012-08-27  6:55 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-08-24 19:31 [PATCH 0/3] Some forcewake fixes Ben Widawsky
2012-08-24 19:31 ` [PATCH 1/3] drm/i915: Extract forcewake ack timeout Ben Widawsky
2012-08-24 19:31 ` [PATCH 2/3] drm/i915: Change forcewake timeout to 2ms Ben Widawsky
2012-08-27  6:59   ` Jani Nikula [this message]
2012-08-28 15:51     ` Ben Widawsky
2012-08-28 16:00       ` Daniel Vetter
2012-08-28 16:07         ` Ben Widawsky
2012-08-28 16:27           ` Daniel Vetter
2012-08-24 19:31 ` [PATCH 3/3] drm/i915: Never read FORCEWAKE Ben Widawsky
2012-08-24 19:48   ` Daniel Vetter

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