[PATCH v4 02/27] cxl/regs: Skip sub-block region request for BAR-owning drivers

[<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 owns the whole component
register BAR, such as vfio-cxl, has already claimed the full BAR, so
the per-sub-block claim collides and the mapping fails.

Add a bar_owned parameter to cxl_pci_setup_regs() and record it in
skip_sub_bar_request on the register map. When set, cxl-core maps the
sub-block without requesting the region and leaves ownership with the
upper driver. cxl_pci passes false and keeps its existing claim,
preserving /dev/mem tooling access to the rest of the component space.

Signed-off-by: Manish Honap <mhonap@nvidia.com>
---
 drivers/cxl/core/pci.c  |  9 ++++++++-
 drivers/cxl/core/regs.c | 32 ++++++++++++++++++++++----------
 drivers/cxl/pci.c       |  4 ++--
 include/cxl/cxl.h       |  3 +++
 include/cxl/pci.h       |  2 +-
 5 files changed, 36 insertions(+), 14 deletions(-)

diff --git a/drivers/cxl/core/pci.c b/drivers/cxl/core/pci.c
index 9d807c1a002c..08d4c955137d 100644
--- a/drivers/cxl/core/pci.c
+++ b/drivers/cxl/core/pci.c
@@ -720,7 +720,7 @@ static int cxl_rcrb_get_comp_regs(struct pci_dev *pdev,
 }
 
 int cxl_pci_setup_regs(struct pci_dev *pdev, enum cxl_regloc_type type,
-		       struct cxl_register_map *map)
+		       struct cxl_register_map *map, bool bar_owned)
 {
 	int rc;
 
@@ -750,6 +750,13 @@ int cxl_pci_setup_regs(struct pci_dev *pdev, enum cxl_regloc_type type,
 		return rc;
 	}
 
+	/*
+	 * A caller that owns the whole register BAR (for example vfio-cxl)
+	 * maps the sub-blocks without claiming them, so the later
+	 * cxl_map_component_regs() does not collide with the full-BAR request.
+	 */
+	map->skip_sub_bar_request = bar_owned;
+
 	return cxl_setup_regs(map);
 }
 EXPORT_SYMBOL_NS_GPL(cxl_pci_setup_regs, "CXL");
diff --git a/drivers/cxl/core/regs.c b/drivers/cxl/core/regs.c
index 989e79383b99..90dd85f322f5 100644
--- a/drivers/cxl/core/regs.c
+++ b/drivers/cxl/core/regs.c
@@ -177,35 +177,47 @@ void cxl_probe_device_regs(struct device *dev, void __iomem *base,
 }
 EXPORT_SYMBOL_NS_GPL(cxl_probe_device_regs, "CXL");
 
-void __iomem *devm_cxl_iomap_block(struct device *dev, resource_size_t addr,
-				   resource_size_t length)
+static void __iomem *__cxl_iomap_block(struct device *dev, resource_size_t addr,
+				       resource_size_t length, bool request)
 {
+	resource_size_t end = addr + length - 1;
 	void __iomem *ret_val;
 	struct resource *res;
 
 	if (WARN_ON_ONCE(addr == CXL_RESOURCE_NONE))
 		return NULL;
 
-	res = devm_request_mem_region(dev, addr, length, dev_name(dev));
-	if (!res) {
-		resource_size_t end = addr + length - 1;
-
-		dev_err(dev, "Failed to request region %pa-%pa\n", &addr, &end);
-		return NULL;
+	/*
+	 * An owning driver (e.g. vfio-cxl) may already hold the whole BAR; a
+	 * sub-block request would then collide with that claim.
+	 */
+	if (request) {
+		res = devm_request_mem_region(dev, addr, length, dev_name(dev));
+		if (!res) {
+			dev_err(dev, "Failed to request region %pa-%pa\n", &addr, &end);
+			return NULL;
+		}
 	}
 
 	ret_val = devm_ioremap(dev, addr, length);
 	if (!ret_val)
-		dev_err(dev, "Failed to map region %pr\n", res);
+		dev_err(dev, "Failed to map region %pa-%pa\n", &addr, &end);
 
 	return ret_val;
 }
+
+void __iomem *devm_cxl_iomap_block(struct device *dev, resource_size_t addr,
+				   resource_size_t length)
+{
+	return __cxl_iomap_block(dev, addr, length, true);
+}
 EXPORT_SYMBOL_NS_GPL(devm_cxl_iomap_block, "CXL");
 
 int cxl_map_component_regs(const struct cxl_register_map *map,
 			   struct cxl_component_regs *regs,
 			   unsigned long map_mask)
 {
+	bool request = !map->skip_sub_bar_request;
 	struct device *host = map->host;
 	struct mapinfo {
 		const struct cxl_reg_map *rmap;
@@ -227,7 +239,7 @@ 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);
+		*(mi->addr) = __cxl_iomap_block(host, addr, length, request);
 		if (!*(mi->addr))
 			return -ENOMEM;
 	}
diff --git a/drivers/cxl/pci.c b/drivers/cxl/pci.c
index bb892dbfdd6d..ec1693c21f61 100644
--- a/drivers/cxl/pci.c
+++ b/drivers/cxl/pci.c
@@ -816,7 +816,7 @@ static int cxl_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
 
 	cxlds->rcd = is_cxl_restricted(pdev);
 
-	rc = cxl_pci_setup_regs(pdev, CXL_REGLOC_RBI_MEMDEV, &map);
+	rc = cxl_pci_setup_regs(pdev, CXL_REGLOC_RBI_MEMDEV, &map, false);
 	if (rc)
 		return rc;
 
@@ -829,7 +829,7 @@ static int cxl_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
 	 * still be useful for management functions so don't return an error.
 	 */
 	rc = cxl_pci_setup_regs(pdev, CXL_REGLOC_RBI_COMPONENT,
-				&cxlds->reg_map);
+				&cxlds->reg_map, false);
 	if (rc)
 		dev_warn(&pdev->dev, "No component registers (%d)\n", rc);
 	else if (!cxlds->reg_map.component_map.ras.valid)
diff --git a/include/cxl/cxl.h b/include/cxl/cxl.h
index efb8ac97bd92..f8e8fddba152 100644
--- a/include/cxl/cxl.h
+++ b/include/cxl/cxl.h
@@ -213,6 +213,8 @@ struct cxl_pmu_reg_map {
  * @resource: physical resource base of the register block
  * @max_size: maximum mapping size to perform register search
  * @reg_type: see enum cxl_regloc_type
+ * @skip_sub_bar_request: set via cxl_pci_setup_regs(); the owning driver holds
+ *			  the BAR, so skip the sub-block claim
  * @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
@@ -223,6 +225,7 @@ struct cxl_register_map {
 	resource_size_t resource;
 	resource_size_t max_size;
 	u8 reg_type;
+	bool skip_sub_bar_request;
 	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 3e0000015871..81a32004a604 100644
--- a/include/cxl/pci.h
+++ b/include/cxl/pci.h
@@ -18,5 +18,5 @@ struct cxl_register_map;
 struct pci_dev;
 
 int cxl_pci_setup_regs(struct pci_dev *pdev, enum cxl_regloc_type type,
-		       struct cxl_register_map *map);
+		       struct cxl_register_map *map, bool bar_owned);
 #endif
-- 
2.25.1