refactor(drm): mark the Vulkan-export output image fallback deprecated

Comment exportImages and its setupImages branch as a deprecated fallback
tracked by neferwl#23, and log the zero-copy output line as a warning
when it is used so reports show it.

commit: 760a0121b387b1f89d2e7be46069dfc939b8526b
author: brice · 15h ago · 2026-10-22 08:13 UTC
parent: f0c31c4
signature: GPG VerifiedCD88F9E564E0102646FB6077A1A07C7C7C3E349D · arch-gpg Verified for the committer email
checks: 1/1

2 files · +13 -2

M docs/dev/architecture.md +1 -1


@@ -29,7 +29,7 @@ About 35 channels connect them, all created in one place, so the full data flow
29	29		A DRM output flips between two images the renderer draws into, with no CPU copy.
30	30
31	31		- Allocation: the images are allocated with GBM (`GBM_BO_USE_SCANOUT \| GBM_BO_USE_RENDERING`), with the modifiers the primary plane lists that the renderer can render into and import. The renderer imports them as Vulkan images, and KMS gets framebuffers made from the same dmabufs. GBM is the display driver's own allocator, so the layouts it picks scan out correctly on every driver.
32		-	- Fallback: when libgbm is missing, GBM allocates nothing usable, or Vulkan or KMS refuses the images, the renderer allocates and exports them itself. Each kind (driver modifier, single-plane, linear) tries GBM, then the renderer. The log line `zero-copy output` names the allocator in its `alloc` field (`gbm` or `vulkan`).
	32	+	- Fallback: when libgbm is missing, GBM allocates nothing usable, or Vulkan or KMS refuses the images, the renderer allocates and exports them itself. Each kind (driver modifier, single-plane, linear) tries GBM, then the renderer. The log line `zero-copy output` names the allocator in its `alloc` field (`gbm` or `vulkan`), and is a warning for `vulkan`. This fallback is deprecated and goes away once GBM is validated on more setups (neferwl#23).
33	33		- Sync: nvidia-drm before 560.35.3 does not wait for `IN_FENCE_FD`. On it, the output waits for each frame's fence on the CPU and commits without one. A client buffer whose fence is still pending is composed, not scanned out, while `IN_FENCE_FD` is unavailable.
34	34
35	35		I also like bringing more tools to the Go ecosystem. NeferWL grew its own libraries along the way, and other Go projects can use them:


@@ -29,7 +29,7 @@ About 35 channels connect them, all created in one place, so the full data flow
29		A DRM output flips between two images the renderer draws into, with no CPU copy.	29		A DRM output flips between two images the renderer draws into, with no CPU copy.
30			30
31		- Allocation: the images are allocated with GBM (`GBM_BO_USE_SCANOUT \| GBM_BO_USE_RENDERING`), with the modifiers the primary plane lists that the renderer can render into and import. The renderer imports them as Vulkan images, and KMS gets framebuffers made from the same dmabufs. GBM is the display driver's own allocator, so the layouts it picks scan out correctly on every driver.	31		- Allocation: the images are allocated with GBM (`GBM_BO_USE_SCANOUT \| GBM_BO_USE_RENDERING`), with the modifiers the primary plane lists that the renderer can render into and import. The renderer imports them as Vulkan images, and KMS gets framebuffers made from the same dmabufs. GBM is the display driver's own allocator, so the layouts it picks scan out correctly on every driver.
32	-	- Fallback: when libgbm is missing, GBM allocates nothing usable, or Vulkan or KMS refuses the images, the renderer allocates and exports them itself. Each kind (driver modifier, single-plane, linear) tries GBM, then the renderer. The log line `zero-copy output` names the allocator in its `alloc` field (`gbm` or `vulkan`).	32	+	- Fallback: when libgbm is missing, GBM allocates nothing usable, or Vulkan or KMS refuses the images, the renderer allocates and exports them itself. Each kind (driver modifier, single-plane, linear) tries GBM, then the renderer. The log line `zero-copy output` names the allocator in its `alloc` field (`gbm` or `vulkan`), and is a warning for `vulkan`. This fallback is deprecated and goes away once GBM is validated on more setups (neferwl#23).
33		- Sync: nvidia-drm before 560.35.3 does not wait for `IN_FENCE_FD`. On it, the output waits for each frame's fence on the CPU and commits without one. A client buffer whose fence is still pending is composed, not scanned out, while `IN_FENCE_FD` is unavailable.	33		- Sync: nvidia-drm before 560.35.3 does not wait for `IN_FENCE_FD`. On it, the output waits for each frame's fence on the CPU and commits without one. A client buffer whose fence is still pending is composed, not scanned out, while `IN_FENCE_FD` is unavailable.
34			34
35		I also like bringing more tools to the Go ecosystem. NeferWL grew its own libraries along the way, and other Go projects can use them:	35		I also like bringing more tools to the Go ecosystem. NeferWL grew its own libraries along the way, and other Go projects can use them:

M internal/adapters/drm/images.go +12 -1


@@ -193,6 +193,9 @@ func (o *Output) setupImages(r ports.Renderer, kind imageKind, cause error, skip
193	193		}
194	194		o.log.Info().Err(gerr).Str("connector", o.conn.name).Int("kind", int(kind)).Str("alloc", allocGBM).Msg("output image allocation")
195	195		}
	196	+	// Deprecated fallback (neferwl#23): renderer-exported images, kept
	197	+	// while GBM is validated on few setups. Remove once no report shows
	198	+	// "alloc":"vulkan" for a few releases.
196	199		if err = o.exportImages(r, mods, kind == imagesSinglePlane); err == nil {
197	200		return kind, nil
198	201		}

@@ -232,6 +235,9 @@ func closeBufs(bufs []ports.DMABuf) {
232	235		}
233	236
234	237		// exportImages makes the renderer's exported targets the output images.
	238	+	//
	239	+	// Deprecated fallback for gbmImages, to remove with neferwl#23. Exported
	240	+	// Vulkan images corrupt scanout on nvidia-drm.
235	241		func (o *Output) exportImages(r ports.Renderer, mods []uint64, singlePlane bool) error {
236	242		o.dropImages(r)
237	243		bufs, err := r.ExportTargets(len(o.fbs), mods, singlePlane)

@@ -266,7 +272,12 @@ func (o *Output) showBufs(r ports.Renderer, bufs []ports.DMABuf, alloc string) e
266	272		return err
267	273		}
268	274		o.planes, o.imageMod = len(bufs[0].Planes), bufs[0].Modifier
269		-	o.log.Info().Str("connector", o.conn.name).Uint64("modifier", bufs[0].Modifier).Int("planes", o.planes).Str("alloc", alloc).Msg("zero-copy output")
	275	+	ev := o.log.Info()
	276	+	if alloc == allocVulkan {
	277	+	// The deprecated fallback is in use: make it visible in reports.
	278	+	ev = o.log.Warn()
	279	+	}
	280	+	ev.Str("connector", o.conn.name).Uint64("modifier", bufs[0].Modifier).Int("planes", o.planes).Str("alloc", alloc).Msg("zero-copy output")
270	281		return nil
271	282		}
272	283

 			}
 			o.log.Info().Err(gerr).Str("connector", o.conn.name).Int("kind", int(kind)).Str("alloc", allocGBM).Msg("output image allocation")
 		}
+		// Deprecated fallback (neferwl#23): renderer-exported images, kept
+		// while GBM is validated on few setups. Remove once no report shows
+		// "alloc":"vulkan" for a few releases.
 		if err = o.exportImages(r, mods, kind == imagesSinglePlane); err == nil {
 			return kind, nil
 		}
 }
 // exportImages makes the renderer's exported targets the output images.
+//
+// Deprecated fallback for gbmImages, to remove with neferwl#23. Exported
+// Vulkan images corrupt scanout on nvidia-drm.
 func (o *Output) exportImages(r ports.Renderer, mods []uint64, singlePlane bool) error {
 	o.dropImages(r)
 	bufs, err := r.ExportTargets(len(o.fbs), mods, singlePlane)
 		return err
 	}
 	o.planes, o.imageMod = len(bufs[0].Planes), bufs[0].Modifier
-	o.log.Info().Str("connector", o.conn.name).Uint64("modifier", bufs[0].Modifier).Int("planes", o.planes).Str("alloc", alloc).Msg("zero-copy output")
+	ev := o.log.Info()
+	if alloc == allocVulkan {
+		// The deprecated fallback is in use: make it visible in reports.
+		ev = o.log.Warn()
+	}
+	ev.Str("connector", o.conn.name).Uint64("modifier", bufs[0].Modifier).Int("planes", o.planes).Str("alloc", alloc).Msg("zero-copy output")
 	return nil
 }