Re: [PATCH] drm/i915/hsw: Disable L3 caching of atomic memory operations.

[Ben Widawsky <ben@bwidawsk.net>]

On Wed, Oct 02, 2013 at 03:03:43PM -0700, Francisco Jerez wrote:
> Otherwise using any atomic memory operation will lock up the GPU due
> to a Haswell hardware bug.  This patch also defines a new DRM param so
> userspace knows that atomics can be used safely.
> 
> Signed-off-by: Francisco Jerez <currojerez@riseup.net>
> ---
>  drivers/gpu/drm/i915/i915_dma.c | 3 +++
>  drivers/gpu/drm/i915/i915_reg.h | 7 +++++++
>  drivers/gpu/drm/i915/intel_pm.c | 6 ++++++
>  include/uapi/drm/i915_drm.h     | 1 +
>  4 files changed, 17 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
> index c27a210..e4fcb3d 100644
> --- a/drivers/gpu/drm/i915/i915_dma.c
> +++ b/drivers/gpu/drm/i915/i915_dma.c
> @@ -1003,6 +1003,9 @@ static int i915_getparam(struct drm_device *dev, void *data,
>  	case I915_PARAM_HAS_EXEC_HANDLE_LUT:
>  		value = 1;
>  		break;
> +	case I915_PARAM_HAS_ATOMICS:
> +		value = 1;
> +		break;
>  	default:
>  		DRM_DEBUG("Unknown parameter %d\n", param->param);
>  		return -EINVAL;
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index c159e1a..611a863 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -3881,6 +3881,9 @@
>  #define GEN7_SQ_CHICKEN_MBCUNIT_CONFIG		0x9030
>  #define  GEN7_SQ_CHICKEN_MBCUNIT_SQINTMOB	(1<<11)
>  
> +#define HSW_SCRATCH1				0xb038
> +#define  HSW_SCRATCH1_L3_DATA_ATOMICS_DISABLE	(1<<27)
> +
>  #define HSW_FUSE_STRAP		0x42014
>  #define  HSW_CDCLK_LIMIT	(1 << 24)
>  
> @@ -4728,6 +4731,10 @@
>  #define GEN7_ROW_CHICKEN2_GT2		0xf4f4
>  #define   DOP_CLOCK_GATING_DISABLE	(1<<0)
>  
> +#define HSW_ROW_CHICKEN3		0xe49c
> +#define  HSW_ROW_CHICKEN3_L3_GLOBAL_ATOMICS_MASK       (1 << 22)
> +#define  HSW_ROW_CHICKEN3_L3_GLOBAL_ATOMICS_DISABLE    (1 << 6)
> +

You do not need the mask bit. We have macros for this:
_MASKED_BIT_ENABLE

>  #define G4X_AUD_VID_DID			(dev_priv->info->display_mmio_offset + 0x62020)
>  #define INTEL_AUDIO_DEVCL		0x808629FB
>  #define INTEL_AUDIO_DEVBLC		0x80862801
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index dd176b7..47f2b2f 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -4955,6 +4955,12 @@ static void haswell_init_clock_gating(struct drm_device *dev)
>  	I915_WRITE(GEN7_L3_CHICKEN_MODE_REGISTER,
>  			GEN7_WA_L3_CHICKEN_MODE);
>  
> +	/* L3 caching of data atomics doesn't work -- disable it. */
> +	I915_WRITE(HSW_SCRATCH1, HSW_SCRATCH1_L3_DATA_ATOMICS_DISABLE);
> +	I915_WRITE(HSW_ROW_CHICKEN3,
> +                   HSW_ROW_CHICKEN3_L3_GLOBAL_ATOMICS_MASK |
> +                   HSW_ROW_CHICKEN3_L3_GLOBAL_ATOMICS_DISABLE);
> +
>  	/* This is required by WaCatErrorRejectionIssue:hsw */
>  	I915_WRITE(GEN7_SQ_CHICKEN_MBCUNIT_CONFIG,
>  			I915_READ(GEN7_SQ_CHICKEN_MBCUNIT_CONFIG) |
> diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
> index 55bb572..fe0f52e 100644
> --- a/include/uapi/drm/i915_drm.h
> +++ b/include/uapi/drm/i915_drm.h
> @@ -335,6 +335,7 @@ typedef struct drm_i915_irq_wait {
>  #define I915_PARAM_HAS_EXEC_NO_RELOC	 25
>  #define I915_PARAM_HAS_EXEC_HANDLE_LUT   26
>  #define I915_PARAM_HAS_WT     	 	 27
> +#define I915_PARAM_HAS_ATOMICS           28
>  
>  typedef struct drm_i915_getparam {
>  	int param;

Also, AFAIK, this workaround still isn't in the bspec, so I think it's a
bit hard for people to review. I'd prefer if we had the bspec updated,
but since they're moving so slowly, and I have the context:

Reviewed-by: Ben Widawsky <ben@bwidawsk.net>

-- 
Ben Widawsky, Intel Open Source Technology Center