linux-kernel - [PATCH v2 4/7] drm/gpuvm: Add a helper to check if two VA can be merged

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Message-ID: <20250702233621.12990-5-caterina.shablia@collabora.com>
Date: Wed,  2 Jul 2025 23:36:06 +0000
From: Caterina Shablia <caterina.shablia@...labora.com>
To: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>,
	Simona Vetter <simona@...ll.ch>
Cc: kernel@...labora.com,
	Caterina Shablia <caterina.shablia@...labora.com>,
	Boris Brezillon <boris.brezillon@...labora.com>,
	dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2 4/7] drm/gpuvm: Add a helper to check if two VA can be merged

From: Boris Brezillon <boris.brezillon@...labora.com>

We are going to add flags/properties that will impact the VA merging
ability. Instead of sprinkling tests all over the place in
__drm_gpuvm_sm_map(), let's add a helper aggregating all these checks
can call it for every existing VA we walk through in the
__drm_gpuvm_sm_map() loop.

Signed-off-by: Boris Brezillon <boris.brezillon@...labora.com>
Signed-off-by: Caterina Shablia <caterina.shablia@...labora.com>
---
 drivers/gpu/drm/drm_gpuvm.c | 47 +++++++++++++++++++++++++++++--------
 1 file changed, 37 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/drm_gpuvm.c b/drivers/gpu/drm/drm_gpuvm.c
index ae201d45e6b8..2df04dfcb6ef 100644
--- a/drivers/gpu/drm/drm_gpuvm.c
+++ b/drivers/gpu/drm/drm_gpuvm.c
@@ -2098,12 +2098,48 @@ op_unmap_cb(const struct drm_gpuvm_ops *fn, void *priv,
 	return fn->sm_step_unmap(&op, priv);
 }
 
+static bool can_merge(struct drm_gpuvm *gpuvm, const struct drm_gpuva *a,
+		      const struct drm_gpuva *b)
+{
+	/* Only GEM-based mappings can be merged, and they must point to
+	 * the same GEM object.
+	 */
+	if (a->gem.obj != b->gem.obj || !a->gem.obj)
+		return false;
+
+	/* Let's keep things simple for now and force all flags to match. */
+	if (a->flags != b->flags)
+		return false;
+
+	/* Order VAs for the rest of the checks. */
+	if (a->va.addr > b->va.addr)
+		swap(a, b);
+
+	/* We assume the caller already checked that VAs overlap or are
+	 * contiguous.
+	 */
+	if (drm_WARN_ON(gpuvm->drm, b->va.addr > a->va.addr + a->va.range))
+		return false;
+
+	/* We intentionally ignore u64 underflows because all we care about
+	 * here is whether the VA diff matches the GEM offset diff.
+	 */
+	return b->va.addr - a->va.addr == b->gem.offset - a->gem.offset;
+}
+
 static int
 __drm_gpuvm_sm_map(struct drm_gpuvm *gpuvm,
 		   const struct drm_gpuvm_ops *ops, void *priv,
 		   const struct drm_gpuvm_map_req *req)
 {
 	struct drm_gpuva *va, *next;
+	struct drm_gpuva reqva = {
+		.va.addr = req->va.addr,
+		.va.range = req->va.range,
+		.gem.offset = req->gem.offset,
+		.gem.obj = req->gem.obj,
+		.flags = req->flags,
+	};
 	u64 req_end = req->va.addr + req->va.range;
 	int ret;
 
@@ -2116,12 +2152,9 @@ __drm_gpuvm_sm_map(struct drm_gpuvm *gpuvm,
 		u64 addr = va->va.addr;
 		u64 range = va->va.range;
 		u64 end = addr + range;
-		bool merge = !!va->gem.obj;
+		bool merge = can_merge(gpuvm, va, &reqva);
 
 		if (addr == req->va.addr) {
-			merge &= obj == req->gem.obj &&
-				 offset == req->gem.offset;
-
 			if (end == req_end) {
 				ret = op_unmap_cb(ops, priv, va, merge);
 				if (ret)
@@ -2163,8 +2196,6 @@ __drm_gpuvm_sm_map(struct drm_gpuvm *gpuvm,
 			};
 			struct drm_gpuva_op_unmap u = { .va = va };
 
-			merge &= obj == req->gem.obj &&
-				 offset + ls_range == req->gem.offset;
 			u.keep = merge;
 
 			if (end == req_end) {
@@ -2196,10 +2227,6 @@ __drm_gpuvm_sm_map(struct drm_gpuvm *gpuvm,
 				break;
 			}
 		} else if (addr > req->va.addr) {
-			merge &= obj == req->gem.obj &&
-				 offset == req->gem.offset +
-					   (addr - req->va.addr);
-
 			if (end == req_end) {
 				ret = op_unmap_cb(ops, priv, va, merge);
 				if (ret)
-- 
2.47.2