Re: [PATCH] drm/xe: Make WA BB part of LRC BO

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

Hi, Matt.

On Wed, 2025-06-11 at 20:19 -0700, Matthew Brost wrote:
> No idea why, but without this GuC context switches randomly fail when
> running IGTs in a loop. Need to follow up why this fixes the
> aforementioned issue but can live with a stable driver for now.
> 
> Fixes: 617d824c5323 ("drm/xe: Add WA BB to capture active context
> utilization")
> Cc: stable@vger.kernel.org
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>

This patch has non-trivial conflicts on drm-xe-fixes. If we need to
have it backported please help resolve the conflicts by:

./dim update-branches
./dim checkout drm-xe-fixes
./dim cherry-pick 3a1edef8f4b5

Fix up conflicts and finalize by

git cherry-pick --continue

And please send the resulting patch to me (including any tags that dim
added).

Thanks,
Thomas



> ---
>  drivers/gpu/drm/xe/xe_lrc.c       | 36 +++++++++++++++--------------
> --
>  drivers/gpu/drm/xe/xe_lrc_types.h |  3 ---
>  2 files changed, 18 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_lrc.c
> b/drivers/gpu/drm/xe/xe_lrc.c
> index 529c6a972a55..a875b93697a5 100644
> --- a/drivers/gpu/drm/xe/xe_lrc.c
> +++ b/drivers/gpu/drm/xe/xe_lrc.c
> @@ -40,6 +40,7 @@
>  
>  #define LRC_PPHWSP_SIZE				SZ_4K
>  #define LRC_INDIRECT_RING_STATE_SIZE		SZ_4K
> +#define LRC_WA_BB_SIZE				SZ_4K
>  
>  static struct xe_device *
>  lrc_to_xe(struct xe_lrc *lrc)
> @@ -910,7 +911,6 @@ static void xe_lrc_finish(struct xe_lrc *lrc)
>  {
>  	xe_hw_fence_ctx_finish(&lrc->fence_ctx);
>  	xe_bo_unpin_map_no_vm(lrc->bo);
> -	xe_bo_unpin_map_no_vm(lrc->bb_per_ctx_bo);
>  }
>  
>  /*
> @@ -973,22 +973,27 @@ struct wa_bb_setup {
>  			 u32 *batch, size_t max_size);
>  };
>  
> +static size_t wa_bb_offset(struct xe_lrc *lrc)
> +{
> +	return lrc->bo->size - LRC_WA_BB_SIZE;
> +}
> +
>  static int setup_wa_bb(struct xe_lrc *lrc, struct xe_hw_engine *hwe)
>  {
> -	const size_t max_size = lrc->bb_per_ctx_bo->size;
> +	const size_t max_size = LRC_WA_BB_SIZE;
>  	static const struct wa_bb_setup funcs[] = {
>  		{ .setup = wa_bb_setup_utilization },
>  	};
>  	ssize_t remain;
>  	u32 *cmd, *buf = NULL;
>  
> -	if (lrc->bb_per_ctx_bo->vmap.is_iomem) {
> +	if (lrc->bo->vmap.is_iomem) {
>  		buf = kmalloc(max_size, GFP_KERNEL);
>  		if (!buf)
>  			return -ENOMEM;
>  		cmd = buf;
>  	} else {
> -		cmd = lrc->bb_per_ctx_bo->vmap.vaddr;
> +		cmd = lrc->bo->vmap.vaddr + wa_bb_offset(lrc);
>  	}
>  
>  	remain = max_size / sizeof(*cmd);
> @@ -1011,13 +1016,14 @@ static int setup_wa_bb(struct xe_lrc *lrc,
> struct xe_hw_engine *hwe)
>  	*cmd++ = MI_BATCH_BUFFER_END;
>  
>  	if (buf) {
> -		xe_map_memcpy_to(gt_to_xe(lrc->gt), &lrc-
> >bb_per_ctx_bo->vmap, 0,
> -				 buf, (cmd - buf) * sizeof(*cmd));
> +		xe_map_memcpy_to(gt_to_xe(lrc->gt), &lrc->bo->vmap,
> +				 wa_bb_offset(lrc), buf,
> +				 (cmd - buf) * sizeof(*cmd));
>  		kfree(buf);
>  	}
>  
> -	xe_lrc_write_ctx_reg(lrc, CTX_BB_PER_CTX_PTR,
> -			     xe_bo_ggtt_addr(lrc->bb_per_ctx_bo) |
> 1);
> +	xe_lrc_write_ctx_reg(lrc, CTX_BB_PER_CTX_PTR,
> xe_bo_ggtt_addr(lrc->bo) +
> +			     wa_bb_offset(lrc) + 1);
>  
>  	return 0;
>  
> @@ -1059,20 +1065,13 @@ static int xe_lrc_init(struct xe_lrc *lrc,
> struct xe_hw_engine *hwe,
>  	 * FIXME: Perma-pinning LRC as we don't yet support moving
> GGTT address
>  	 * via VM bind calls.
>  	 */
> -	lrc->bo = xe_bo_create_pin_map(xe, tile, NULL, lrc_size,
> +	lrc->bo = xe_bo_create_pin_map(xe, tile, NULL,
> +				       lrc_size + LRC_WA_BB_SIZE,
>  				       ttm_bo_type_kernel,
>  				       bo_flags);
>  	if (IS_ERR(lrc->bo))
>  		return PTR_ERR(lrc->bo);
>  
> -	lrc->bb_per_ctx_bo = xe_bo_create_pin_map(xe, tile, NULL,
> SZ_4K,
> -						 
> ttm_bo_type_kernel,
> -						  bo_flags);
> -	if (IS_ERR(lrc->bb_per_ctx_bo)) {
> -		err = PTR_ERR(lrc->bb_per_ctx_bo);
> -		goto err_lrc_finish;
> -	}
> -
>  	lrc->size = lrc_size;
>  	lrc->ring.size = ring_size;
>  	lrc->ring.tail = 0;
> @@ -1860,7 +1859,8 @@ struct xe_lrc_snapshot
> *xe_lrc_snapshot_capture(struct xe_lrc *lrc)
>  	snapshot->seqno = xe_lrc_seqno(lrc);
>  	snapshot->lrc_bo = xe_bo_get(lrc->bo);
>  	snapshot->lrc_offset = xe_lrc_pphwsp_offset(lrc);
> -	snapshot->lrc_size = lrc->bo->size - snapshot->lrc_offset;
> +	snapshot->lrc_size = lrc->bo->size - snapshot->lrc_offset -
> +		LRC_WA_BB_SIZE;
>  	snapshot->lrc_snapshot = NULL;
>  	snapshot->ctx_timestamp =
> lower_32_bits(xe_lrc_ctx_timestamp(lrc));
>  	snapshot->ctx_job_timestamp = xe_lrc_ctx_job_timestamp(lrc);
> diff --git a/drivers/gpu/drm/xe/xe_lrc_types.h
> b/drivers/gpu/drm/xe/xe_lrc_types.h
> index ae24cf6f8dd9..883e550a9423 100644
> --- a/drivers/gpu/drm/xe/xe_lrc_types.h
> +++ b/drivers/gpu/drm/xe/xe_lrc_types.h
> @@ -53,9 +53,6 @@ struct xe_lrc {
>  
>  	/** @ctx_timestamp: readout value of CTX_TIMESTAMP on last
> update */
>  	u64 ctx_timestamp;
> -
> -	/** @bb_per_ctx_bo: buffer object for per context batch wa
> buffer */
> -	struct xe_bo *bb_per_ctx_bo;
>  };
>  
>  struct xe_lrc_snapshot;