[PATCH v6 02/31] cxl/regs: Let a BAR-owning driver own the component register block

[<mhonap@nvidia.com>]

From: Manish Honap <mhonap@nvidia.com>

cxl_map_component_regs() claims each mapped sub-block with
devm_request_mem_region(). A driver that requests the whole component
register BAR itself, such as vfio-cxl, would then collide with that
claim and fail to map the HDM decoder and RAS blocks.

Add cxl_reg_map_set_owned_resource() so such a driver records the
resource it already owns, the whole component register BAR, on the
register map.

Skip the sub-block request for a block inside that resource, and fail with
-ENXIO for a block outside it.

Assisted-by: LLM
Signed-off-by: Manish Honap <mhonap@nvidia.com>
---
 drivers/cxl/core/regs.c | 46 +++++++++++++++++++++++++++++++++++++++--
 include/cxl/cxl.h       |  2 ++
 include/cxl/pci.h       |  3 +++
 3 files changed, 49 insertions(+), 2 deletions(-)

diff --git a/drivers/cxl/core/regs.c b/drivers/cxl/core/regs.c
index 9235520b2f4e..c3df99de92c3 100644
--- a/drivers/cxl/core/regs.c
+++ b/drivers/cxl/core/regs.c
@@ -216,6 +216,39 @@ void __iomem *devm_cxl_iomap_block(struct device *dev, resource_size_t addr,
 }
 EXPORT_SYMBOL_NS_GPL(devm_cxl_iomap_block, "CXL");
 
+/**
+ * cxl_reg_map_set_owned_resource() - record the BAR a driver owns
+ * @map: register map of the component register block
+ * @res: resource of the whole component register BAR, which the caller
+ *	requests itself, before or after this call
+ *
+ * A driver that requests the whole component register BAR itself, such as
+ * vfio-cxl, records that BAR here. cxl_map_component_regs() then maps the
+ * blocks inside @res without requesting them again and refuses any block
+ * outside it. A register map has at most one owned resource.
+ *
+ * Call this after cxl_pci_setup_regs() has filled @map: enumeration rewrites
+ * the whole map and drops a previously recorded owned resource.
+ *
+ * Return: 0 on success, -EBUSY if an owned resource is already set, or
+ * -EINVAL if @map has not been set up or its block lies outside @res.
+ */
+int cxl_reg_map_set_owned_resource(struct cxl_register_map *map,
+				   struct resource *res)
+{
+	struct resource block = DEFINE_RES_MEM(map->resource, map->max_size);
+
+	if (WARN_ON_ONCE(map->owned))
+		return -EBUSY;
+	if (WARN_ON_ONCE(map->resource == CXL_RESOURCE_NONE ||
+			 !resource_contains(res, &block)))
+		return -EINVAL;
+
+	map->owned = res;
+	return 0;
+}
+EXPORT_SYMBOL_NS_GPL(cxl_reg_map_set_owned_resource, "CXL");
+
 int cxl_map_component_regs(const struct cxl_register_map *map,
 			   struct cxl_component_regs *regs,
 			   unsigned long map_mask)
@@ -234,6 +267,7 @@ int cxl_map_component_regs(const struct cxl_register_map *map,
 		struct mapinfo *mi = &mapinfo[i];
 		resource_size_t addr;
 		resource_size_t length;
+		struct resource res;
 
 		if (!mi->rmap->valid)
 			continue;
@@ -241,8 +275,16 @@ int cxl_map_component_regs(const struct cxl_register_map *map,
 			continue;
 		addr = map->resource + mi->rmap->offset;
 		length = mi->rmap->size;
-		*(mi->addr) = devm_cxl_iomap_block(host, addr, length);
-		if (!*(mi->addr))
+		res = DEFINE_RES_MEM(addr, length);
+
+		if (map->owned) {
+			if (!resource_contains(map->owned, &res))
+				return -ENXIO;
+			*mi->addr = devm_cxl_ioremap_block(host, addr, length);
+		} else {
+			*mi->addr = devm_cxl_iomap_block(host, addr, length);
+		}
+		if (!*mi->addr)
 			return -ENOMEM;
 	}
 
diff --git a/include/cxl/cxl.h b/include/cxl/cxl.h
index 3e70f74685b6..4bd0fec4951f 100644
--- a/include/cxl/cxl.h
+++ b/include/cxl/cxl.h
@@ -153,6 +153,7 @@ struct cxl_pmu_reg_map {
  * @bar: PCI BAR containing the register block
  * @bar_offset: register block offset relative to @bar
  * @reg_type: see enum cxl_regloc_type
+ * @owned: driver-owned resource whose sub-blocks are mapped without re-requesting
  * @component_map: cxl_reg_map for component registers
  * @device_map: cxl_reg_maps for device registers
  * @pmu_map: cxl_reg_maps for CXL Performance Monitoring Units
@@ -165,6 +166,7 @@ struct cxl_register_map {
 	int bar;
 	resource_size_t bar_offset;
 	u8 reg_type;
+	struct resource *owned;
 	union {
 		struct cxl_component_reg_map component_map;
 		struct cxl_device_reg_map device_map;
diff --git a/include/cxl/pci.h b/include/cxl/pci.h
index b15d7e415e27..0b74819fea6d 100644
--- a/include/cxl/pci.h
+++ b/include/cxl/pci.h
@@ -18,9 +18,12 @@ enum cxl_regloc_type {
 
 struct cxl_register_map;
 struct pci_dev;
+struct resource;
 
 int cxl_pci_setup_regs(struct pci_dev *pdev, enum cxl_regloc_type type,
 		       struct cxl_register_map *map);
+int cxl_reg_map_set_owned_resource(struct cxl_register_map *map,
+				   struct resource *res);
 int cxl_find_regblock(struct pci_dev *pdev, enum cxl_regloc_type type,
 		      struct cxl_register_map *map);
 int cxl_setup_regs(struct cxl_register_map *map);
-- 
2.53.0