[Intel-xe] [PATCH 1/6] drm/xe: add xe_ttm_stolen_cpu_access_needs_ggtt()

[Gwan-gyeong Mun]

Looks good to me.
By the way, the commit message explained only the case of smallbar, is 
there a way to access stolen memory in the case of dgpu resizable-bar?

Reviewed-by: Gwan-gyeong Mun <gwan-gyeong.mun at intel.com>

On 3/1/23 4:48 PM, Matthew Auld wrote:
> xe_ttm_stolen_cpu_inaccessible() was originally meant to just cover the
> case where stolen is not directly CPU accessible on some older
> integrated platforms, and as such a GGTT mapping was also required for
> CPU access (as per the check in xe_bo_create_pin_map_at()).
> 
> However with small-bar systems on dgfx we have one more case where
> stolen is also inaccessible, however here we don't have any fallback
> GGTT mode for CPU access. Fix the check in xe_bo_create_pin_map_at() to
> make this distinction clear. In such a case the later vmap() will fail
> anyway.
> 
> Suggested-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
> Signed-off-by: Matthew Auld <matthew.auld at intel.com>
> ---
>   drivers/gpu/drm/xe/xe_bo.c             |  2 +-
>   drivers/gpu/drm/xe/xe_ttm_stolen_mgr.c | 14 ++++++++++++++
>   drivers/gpu/drm/xe/xe_ttm_stolen_mgr.h |  1 +
>   3 files changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
> index 2bfd3f6f2e9a..876f77669104 100644
> --- a/drivers/gpu/drm/xe/xe_bo.c
> +++ b/drivers/gpu/drm/xe/xe_bo.c
> @@ -1151,7 +1151,7 @@ struct xe_bo *xe_bo_create_pin_map_at(struct xe_device *xe, struct xe_gt *gt,
>   	u64 end = offset == ~0ull ? offset : start + size;
>   
>   	if (flags & XE_BO_CREATE_STOLEN_BIT &&
> -	    xe_ttm_stolen_cpu_inaccessible(xe))
> +	    xe_ttm_stolen_cpu_access_needs_ggtt(xe))
>   		flags |= XE_BO_CREATE_GGTT_BIT;
>   
>   	bo = xe_bo_create_locked_range(xe, gt, vm, size, start, end, type, flags);
> diff --git a/drivers/gpu/drm/xe/xe_ttm_stolen_mgr.c b/drivers/gpu/drm/xe/xe_ttm_stolen_mgr.c
> index 2e8d07ad42ae..4bf373a03d64 100644
> --- a/drivers/gpu/drm/xe/xe_ttm_stolen_mgr.c
> +++ b/drivers/gpu/drm/xe/xe_ttm_stolen_mgr.c
> @@ -66,6 +66,20 @@ bool xe_ttm_stolen_cpu_inaccessible(struct xe_device *xe)
>   	return !mgr->io_base || GRAPHICS_VERx100(xe) < 1270;
>   }
>   
> +/**
> + * xe_ttm_stolen_needs_ggtt - If we can't directly CPU access stolen, can we
> + * then fallback to mapping through the GGTT.
> + * @xe: xe device
> + *
> + * Some older integrated platforms don't support reliable CPU access for stolen,
> + * however on such hardware we can always use the mappable part of the GGTT for
> + * CPU access. Check if that's the case for this device.
> + */
> +bool xe_ttm_stolen_cpu_access_needs_ggtt(struct xe_device *xe)
> +{
> +	return xe_ttm_stolen_cpu_inaccessible(xe) && !IS_DGFX(xe);
> +}
> +
>   static s64 detect_bar2_dgfx(struct xe_device *xe, struct xe_ttm_stolen_mgr *mgr)
>   {
>   	struct pci_dev *pdev = to_pci_dev(xe->drm.dev);
> diff --git a/drivers/gpu/drm/xe/xe_ttm_stolen_mgr.h b/drivers/gpu/drm/xe/xe_ttm_stolen_mgr.h
> index 2fda97b97a05..e210dada636e 100644
> --- a/drivers/gpu/drm/xe/xe_ttm_stolen_mgr.h
> +++ b/drivers/gpu/drm/xe/xe_ttm_stolen_mgr.h
> @@ -15,6 +15,7 @@ struct xe_device;
>   void xe_ttm_stolen_mgr_init(struct xe_device *xe);
>   int xe_ttm_stolen_io_mem_reserve(struct xe_device *xe, struct ttm_resource *mem);
>   bool xe_ttm_stolen_cpu_inaccessible(struct xe_device *xe);
> +bool xe_ttm_stolen_cpu_access_needs_ggtt(struct xe_device *xe);
>   u64 xe_ttm_stolen_io_offset(struct xe_bo *bo, u32 offset);
>   u64 xe_ttm_stolen_gpu_offset(struct xe_device *xe);
>