Re: [PATCH v4 17/18] drm/i915: Wa32bitGeneralStateOffset & Wa32bitInstructionBaseOffset

[Michel Thierry <michel.thierry@intel.com>]

On 7/7/2015 4:15 PM, Michel Thierry wrote:
> There are some allocations that must be only referenced by 32-bit
> offsets. To limit the chances of having the first 4GB already full,
> objects not requiring this workaround use DRM_MM_SEARCH_BELOW/
> DRM_MM_CREATE_TOP flags
>
> In specific, any resource used with flat/heapless (0x00000000-0xfffff000)
> General State Heap (GSH) or Intructions State Heap (ISH) must be in a
> 32-bit range, because the General State Offset and Instruction State
> Offset are limited to 32-bits.
>
> Objects must have EXEC_OBJECT_SUPPORTS_48B_ADDRESS flag to indicate if
> they can be allocated above the 32-bit address range. To limit the
> chances of having the first 4GB already full, objects will use
> DRM_MM_SEARCH_BELOW + DRM_MM_CREATE_TOP flags when possible.
>
> v2: Changed flag logic from neeeds_32b, to supports_48b.
> v3: Moved 48-bit support flag back to exec_object. (Chris, Daniel)
> v4: Split pin flags into PIN_ZONE_4G and PIN_HIGH; update PIN_OFFSET_MASK
> to use last PIN_ defined instead of hard-coded value; use correct limit
> check in eb_vma_misplaced. (Chris)
> v5: Don't touch PIN_OFFSET_MASK and update workaround comment (Chris)
>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> (v4)
> Signed-off-by: Michel Thierry <michel.thierry@intel.com>
> ---
>   drivers/gpu/drm/i915/i915_drv.h            |  2 ++
>   drivers/gpu/drm/i915/i915_gem.c            | 14 ++++++++++++--
>   drivers/gpu/drm/i915/i915_gem_execbuffer.c | 13 +++++++++++++
>   include/uapi/drm/i915_drm.h                |  3 ++-
>   4 files changed, 29 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 4a30a73..fc88e58 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -2772,6 +2772,8 @@ void i915_gem_vma_destroy(struct i915_vma *vma);
>   #define PIN_OFFSET_BIAS        (1<<3)
>   #define PIN_USER       (1<<4)
>   #define PIN_UPDATE     (1<<5)
> +#define PIN_ZONE_4G    (1<<6)
> +#define PIN_HIGH       (1<<7)
>   #define PIN_OFFSET_MASK (~4095)
>   int __must_check
>   i915_gem_object_pin(struct drm_i915_gem_object *obj,
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index ebfb789..b13900d 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -3720,6 +3720,8 @@ i915_gem_object_bind_to_vm(struct drm_i915_gem_object *obj,
>          struct drm_i915_private *dev_priv = dev->dev_private;
>          u32 fence_alignment, unfenced_alignment;
>          u64 size, fence_size;
> +       u32 search_flag = DRM_MM_SEARCH_DEFAULT;
> +       u32 alloc_flag = DRM_MM_CREATE_DEFAULT;
>          u64 start =
>                  flags & PIN_OFFSET_BIAS ? flags & PIN_OFFSET_MASK : 0;
>          u64 end =
> @@ -3761,6 +3763,14 @@ i915_gem_object_bind_to_vm(struct drm_i915_gem_object *obj,
>                                                     obj->tiling_mode,
>                                                     false);
>                  size = flags & PIN_MAPPABLE ? fence_size : obj->base.size;
> +
> +               if (flags & PIN_HIGH) {
> +                       search_flag = DRM_MM_SEARCH_BELOW;
> +                       alloc_flag = DRM_MM_CREATE_TOP;
> +               }
> +
> +               if (flags & PIN_ZONE_4G)
> +                       end = (1ULL << 32);
Hi Chris,
second thoughts on this... would PIN_HIGH & PIN_ZONE_4G be a problem if 
someone mixes a 64-bit kernel with 32-bit userland?
Maybe it's safer to set end = (1ULL << 32) - PAGE_SIZE.

>          }
>
>          if (alignment == 0)

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