[PATCH 1/2] drm/xe: Move DSB l2 flush to a more sensible place

[Lucas De Marchi]

On Fri, Jun 06, 2025 at 11:45:47AM +0100, Matthew Auld wrote:
>From: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
>
>Flushing l2 is only needed after all data has been written.
>
>Fixes: 01570b446939 ("drm/xe/bmg: implement Wa_16023588340")
>Signed-off-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
>Cc: Matthew Auld <matthew.auld at intel.com>
>Cc: <stable at vger.kernel.org> # v6.12+
>Reviewed-by: Matthew Auld <matthew.auld at intel.com>
>Signed-off-by: Matthew Auld <matthew.auld at intel.com>
>---
> drivers/gpu/drm/xe/display/xe_dsb_buffer.c | 11 ++++-------
> 1 file changed, 4 insertions(+), 7 deletions(-)
>
>diff --git a/drivers/gpu/drm/xe/display/xe_dsb_buffer.c b/drivers/gpu/drm/xe/display/xe_dsb_buffer.c
>index f95375451e2f..9f941fc2e36b 100644
>--- a/drivers/gpu/drm/xe/display/xe_dsb_buffer.c
>+++ b/drivers/gpu/drm/xe/display/xe_dsb_buffer.c
>@@ -17,10 +17,7 @@ u32 intel_dsb_buffer_ggtt_offset(struct intel_dsb_buffer *dsb_buf)
>
> void intel_dsb_buffer_write(struct intel_dsb_buffer *dsb_buf, u32 idx, u32 val)
> {
>-	struct xe_device *xe = dsb_buf->vma->bo->tile->xe;
>-
> 	iosys_map_wr(&dsb_buf->vma->bo->vmap, idx * 4, u32, val);
>-	xe_device_l2_flush(xe);
> }
>
> u32 intel_dsb_buffer_read(struct intel_dsb_buffer *dsb_buf, u32 idx)
>@@ -30,12 +27,9 @@ u32 intel_dsb_buffer_read(struct intel_dsb_buffer *dsb_buf, u32 idx)
>
> void intel_dsb_buffer_memset(struct intel_dsb_buffer *dsb_buf, u32 idx, u32 val, size_t size)
> {
>-	struct xe_device *xe = dsb_buf->vma->bo->tile->xe;
>-
> 	WARN_ON(idx > (dsb_buf->buf_size - size) / sizeof(*dsb_buf->cmd_buf));
>
> 	iosys_map_memset(&dsb_buf->vma->bo->vmap, idx * 4, val, size);
>-	xe_device_l2_flush(xe);
> }
>
> bool intel_dsb_buffer_create(struct intel_crtc *crtc, struct intel_dsb_buffer *dsb_buf, size_t size)
>@@ -74,9 +68,12 @@ void intel_dsb_buffer_cleanup(struct intel_dsb_buffer *dsb_buf)
>
> void intel_dsb_buffer_flush_map(struct intel_dsb_buffer *dsb_buf)

assuming the calls to this function are already in the right place,

Reviewed-by: Lucas De Marchi <lucas.demarchi at intel.com>

... but it seems quite fragile as we are exposing the other the
functions writing to it. Not something introduced here though.


Lucas De Marchi

> {
>+	struct xe_device *xe = dsb_buf->vma->bo->tile->xe;
>+
> 	/*
> 	 * The memory barrier here is to ensure coherency of DSB vs MMIO,
> 	 * both for weak ordering archs and discrete cards.
> 	 */
>-	xe_device_wmb(dsb_buf->vma->bo->tile->xe);
>+	xe_device_wmb(xe);
>+	xe_device_l2_flush(xe);
> }
>-- 
>2.49.0
>