[PATCH v2 2/6] drm/xe: Use iosys_map helpers for WA BB emission

[Lucas De Marchi]

On Mon, Jun 02, 2025 at 12:19:52PM +0100, Tvrtko Ursulin wrote:
>To properly support discrete GPUs on all platforms it is required to use
>the iosys_map helpers.
>
>To fix we emit the WA BB into an on stack buffer and copy it over using
>xe_map_memcpy_to().

For https://lore.kernel.org/intel-xe/20250523-wa-bb-cmds-v1-0-40b337f71bcd@intel.com
we will extend the WA BB to other things (and that is the first
additional user). I don't think we can keep it on stack. For my next
version I was adding the patch below to allocate the buffer. Let me know
what you think.

commit 28dbdf201133d92b0e0b0a0139eae7fe5eb9e33b
Author: Lucas De Marchi <lucas.demarchi at intel.com>
Date:   Fri May 30 16:29:51 2025 -0700

     drm/xe/lrc: Use a temporary buffer for WA BB
     
     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>
     Signed-off-by: Lucas De Marchi <lucas.demarchi at intel.com>

diff --git a/drivers/gpu/drm/xe/xe_lrc.c b/drivers/gpu/drm/xe/xe_lrc.c
index 63d74e27f54cf..1b835d7efca2b 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);
+		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;
  
Lucas De Marchi