[PATCH 1/2] drm/xe/lrc: Use a temporary buffer for WA BB

[Matthew Brost]

On Wed, Jun 04, 2025 at 08:03:05AM -0700, Lucas De Marchi wrote:
> In case the BO is in iomem, we can't simply take the vaddr and write to
> it. Instead, prepare a separate buffer that is later copied into io
> memory. Right now it's just a few words that could be using
> xe_map_write32(), but the intention is to grow the WA BB for other
> uses.
> 
> Fixes: 82b98cadb01f ("drm/xe: Add WA BB to capture active context utilization")
> Cc: Umesh Nerlige Ramappa <umesh.nerlige.ramappa at intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at igalia.com>

Reviewed-by: Matthew Brost <matthew.brost at intel.com>

> Signed-off-by: Lucas De Marchi <lucas.demarchi at intel.com>
> ---
>  drivers/gpu/drm/xe/xe_lrc.c | 24 ++++++++++++++++++++----
>  1 file changed, 20 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_lrc.c b/drivers/gpu/drm/xe/xe_lrc.c
> index 63d74e27f54cf..bf7c3981897de 100644
> --- a/drivers/gpu/drm/xe/xe_lrc.c
> +++ b/drivers/gpu/drm/xe/xe_lrc.c
> @@ -941,11 +941,18 @@ static void xe_lrc_finish(struct xe_lrc *lrc)
>   * store it in the PPHSWP.
>   */
>  #define CONTEXT_ACTIVE 1ULL
> -static void xe_lrc_setup_utilization(struct xe_lrc *lrc)
> +static int xe_lrc_setup_utilization(struct xe_lrc *lrc)
>  {
> -	u32 *cmd;
> +	u32 *cmd, *buf = NULL;
>  
> -	cmd = lrc->bb_per_ctx_bo->vmap.vaddr;
> +	if (lrc->bb_per_ctx_bo->vmap.is_iomem) {
> +		buf = kmalloc(lrc->bb_per_ctx_bo->size, GFP_KERNEL);
> +		if (!buf)
> +			return -ENOMEM;
> +		cmd = buf;
> +	} else {
> +		cmd = lrc->bb_per_ctx_bo->vmap.vaddr;
> +	}
>  
>  	*cmd++ = MI_STORE_REGISTER_MEM | MI_SRM_USE_GGTT | MI_SRM_ADD_CS_OFFSET;
>  	*cmd++ = ENGINE_ID(0).addr;
> @@ -966,9 +973,16 @@ static void xe_lrc_setup_utilization(struct xe_lrc *lrc)
>  
>  	*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));
> +		kfree(buf);
> +	}
> +
>  	xe_lrc_write_ctx_reg(lrc, CTX_BB_PER_CTX_PTR,
>  			     xe_bo_ggtt_addr(lrc->bb_per_ctx_bo) | 1);
>  
> +	return 0;
>  }
>  
>  #define PVC_CTX_ASID		(0x2e + 1)
> @@ -1125,7 +1139,9 @@ static int xe_lrc_init(struct xe_lrc *lrc, struct xe_hw_engine *hwe,
>  	map = __xe_lrc_start_seqno_map(lrc);
>  	xe_map_write32(lrc_to_xe(lrc), &map, lrc->fence_ctx.next_seqno - 1);
>  
> -	xe_lrc_setup_utilization(lrc);
> +	err = xe_lrc_setup_utilization(lrc);
> +	if (err)
> +		goto err_lrc_finish;
>  
>  	return 0;
>  
> 
> -- 
> 2.49.0
>