Re: [PATCH 02/10] drm/i915: Implement w/a for sporadic read failures on waking from rc6

[Ben Widawsky <ben@bwidawsk.net>]

On Mon,  2 Jul 2012 11:51:03 -0300
Eugeni Dodonov <eugeni.dodonov@intel.com> wrote:

> From: Chris Wilson <chris@chris-wilson.co.uk>
> 
> As a w/a to prevent reads sporadically returning 0, we need to wait for
> the GT thread to return to TC0 before proceeding to read the registers.
> 
> v2: adapt for Haswell changes (Eugeni).
> 
> v3: use wait_for_atomic_us for thread status polling.
> 
> v3: *really* use wait_for_atomic for polling.
> 
> References: https://bugs.freedesktop.org/show_bug.cgi?id=50243
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Signed-off-by: Eugeni Dodonov <eugeni.dodonov@intel.com>

meh, I cannot find the register defs, but since I've heard about this
through the grapevine:
Acked-by: Ben Widawsky <ben@bwidawsk.net>
> ---
>  drivers/gpu/drm/i915/i915_drv.c | 22 ++++++++++++++++++++++
>  drivers/gpu/drm/i915/i915_reg.h |  4 ++++
>  2 files changed, 26 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
> index 928b667..a4ea4a9 100644
> --- a/drivers/gpu/drm/i915/i915_drv.c
> +++ b/drivers/gpu/drm/i915/i915_drv.c
> @@ -433,6 +433,22 @@ bool i915_semaphore_is_enabled(struct drm_device *dev)
>  	return 1;
>  }
>  
> +static void __gen6_gt_wait_for_thread_c0(struct drm_i915_private *dev_priv)
> +{
> +	u32 gt_thread_status_mask;
> +
> +	if (IS_HASWELL(dev_priv->dev))
> +		gt_thread_status_mask = GEN6_GT_THREAD_STATUS_CORE_MASK_HSW;
> +	else
> +		gt_thread_status_mask = GEN6_GT_THREAD_STATUS_CORE_MASK;
> +
> +	/* w/a for a sporadic read returning 0 by waiting for the GT
> +	 * thread to wake up.
> +	 */
> +	if (wait_for_atomic_us((I915_READ_NOTRACE(GEN6_GT_THREAD_STATUS_REG) & gt_thread_status_mask) == 0, 500))
> +		DRM_ERROR("GT thread status wait timed out\n");
> +}
> +
>  static void __gen6_gt_force_wake_get(struct drm_i915_private *dev_priv)
>  {
>  	if (wait_for_atomic_us((I915_READ_NOTRACE(FORCEWAKE_ACK) & 1) == 0, 500))
> @@ -442,6 +458,8 @@ static void __gen6_gt_force_wake_get(struct drm_i915_private *dev_priv)
>  
>  	if (wait_for_atomic_us((I915_READ_NOTRACE(FORCEWAKE_ACK) & 1), 500))
>  		DRM_ERROR("Force wake wait timed out\n");
> +
> +	__gen6_gt_wait_for_thread_c0(dev_priv);
>  }
>  
>  static void __gen6_gt_force_wake_mt_get(struct drm_i915_private *dev_priv)
> @@ -453,6 +471,8 @@ static void __gen6_gt_force_wake_mt_get(struct drm_i915_private *dev_priv)
>  
>  	if (wait_for_atomic_us((I915_READ_NOTRACE(FORCEWAKE_MT_ACK) & 1), 500))
>  		DRM_ERROR("Force wake wait timed out\n");
> +
> +	__gen6_gt_wait_for_thread_c0(dev_priv);
>  }
>  
>  /*
> @@ -538,6 +558,8 @@ static void vlv_force_wake_get(struct drm_i915_private *dev_priv)
>  
>  	if (wait_for_atomic_us((I915_READ_NOTRACE(FORCEWAKE_ACK_VLV) & 1), 500))
>  		DRM_ERROR("Force wake wait timed out\n");
> +
> +	__gen6_gt_wait_for_thread_c0(dev_priv);
>  }
>  
>  static void vlv_force_wake_put(struct drm_i915_private *dev_priv)
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index d8f516b..20f7f0d 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -1458,6 +1458,10 @@
>  #define DDRMPLL1		0X12c20
>  #define PEG_BAND_GAP_DATA	0x14d68
>  
> +#define GEN6_GT_THREAD_STATUS_REG 0x13805c
> +#define GEN6_GT_THREAD_STATUS_CORE_MASK 0x7
> +#define GEN6_GT_THREAD_STATUS_CORE_MASK_HSW (0x7 | (0x07 << 16))
> +
>  #define GEN6_GT_PERF_STATUS	0x145948
>  #define GEN6_RP_STATE_LIMITS	0x145994
>  #define GEN6_RP_STATE_CAP	0x145998



-- 
Ben Widawsky, Intel Open Source Technology Center