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

[Lucas De Marchi]

On Mon, Jun 02, 2025 at 04:22:47PM +0100, Tvrtko Ursulin wrote:
>
>On 02/06/2025 15:56, Lucas De Marchi wrote:
>>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 at 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.
>
>Works for me I think.
>
>I mean I don't exactly see yet how you will make it work for multiple 
>users adding stuff to the same wa bb, like will you consider a shared 

this is done via configfs that is read on probe only.... mainly intended
for testing new workarounds and tuning before changing anything in
xe.ko.

>buffer passed down from the level up or what, but in any case I can 
>probably adapt my series quite easily.
>
>In summary, you suggest my series waits for yours to land first?

Let me post this fix separately.

Lucas De Marchi

>
>Regards,
>
>Tvrtko
>
>>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
>