[RFC PATCH 2/4] PCI/CXL: Populate and insert/remove pdev->coh_resource[]

[Ankit Agrawal <ankita@nvidia.com>]

On systems with precommitted HDM decoders, the firmware programs
the decoders before any software runs. This range also stays constant
over the runs.

Snapshot precommitted CXL HDM decoder ranges into a new
pdev->coh_resource[] array, so later code has a known-good source for
a device coherent (CXL) windows without re-scanning decoder
registers.

Signed-off-by: Ankit Agrawal <ankita@nvidia.com>
Assisted-by: Claude:sonnet-5
---
 drivers/cxl/core/resource.c | 52 ++++++++++++++++++++++++++++++++++++-
 include/linux/pci.h         | 14 ++++++++++
 2 files changed, 65 insertions(+), 1 deletion(-)

diff --git a/drivers/cxl/core/resource.c b/drivers/cxl/core/resource.c
index 3422139ae3ab..4d2082c8e321 100644
--- a/drivers/cxl/core/resource.c
+++ b/drivers/cxl/core/resource.c
@@ -404,6 +404,46 @@ static struct cxl_hdm_info *cxl_pci_hdm_read_info(struct pci_dev *pdev,
 	return ERR_PTR(pcibios_err_to_errno(rc));
 }
 
+/*
+ * Snapshot committed decoders into pdev->coh_resource[] which is called
+ * once per pdev before any driver can bind, so a populated entry is
+ * always firmware-committed and not driver-committed.
+ *
+ * Insert each entry into iomem_resource for /proc/iomem visibility and
+ * conflict detection.
+ */
+static void cxl_populate_coh_resource(struct pci_dev *pdev,
+				      struct cxl_hdm_info *info)
+{
+	int count = min(info->decoder_count, PCI_CXL_MAX_COHERENT_RANGES);
+
+	for (int i = 0; i < count; i++) {
+		struct cxl_decoder_config *config = &info->settings[i].config;
+		struct resource *res = &pdev->coh_resource[i];
+		struct resource *conflict;
+
+		if (!(config->flags & CXL_DECODER_F_ENABLE))
+			continue;
+
+		*res = DEFINE_RES_NAMED_DESC(config->hpa_range.start,
+					     range_len(&config->hpa_range),
+					     "CXL coherent memory",
+					     IORESOURCE_MEM, IORES_DESC_NONE);
+
+		conflict = insert_resource_conflict(&iomem_resource, res);
+		if (conflict) {
+			pci_warn(pdev,
+				 "CXL coherent range: decoder%d %pR conflicts with %s %pR, leaving unpopulated\n",
+				 i, res, conflict->name, conflict);
+			memset(res, 0, sizeof(*res));
+			continue;
+		}
+
+		pci_info(pdev, "CXL coherent range: decoder%d precommitted, populated %pR\n",
+			 i, res);
+	}
+}
+
 static int __pci_cxl_hdm_cache_init(struct pci_dev *pdev)
 {
 	struct cxl_register_map map = { };
@@ -442,8 +482,10 @@ static int __pci_cxl_hdm_cache_init(struct pci_dev *pdev)
 	struct cxl_hdm_info *info __free(kfree) = read_info;
 	guard(rwsem_write)(&cxl_rwsem.dpa);
 	/* Another initializer may have published while we read MMIO. */
-	if (!pdev->hdm)
+	if (!pdev->hdm) {
+		cxl_populate_coh_resource(pdev, info);
 		pdev->hdm = no_free_ptr(info);
+	}
 
 	return 0;
 }
@@ -466,6 +508,14 @@ void pci_cxl_hdm_cache_release(struct pci_dev *pdev)
 	info = pdev->hdm;
 	/* Unpublish before freeing so subsequent readers cannot use stale state. */
 	pdev->hdm = NULL;
+
+	for (int i = 0; i < PCI_CXL_MAX_COHERENT_RANGES; i++) {
+		struct resource *res = &pdev->coh_resource[i];
+
+		if (res->parent)
+			remove_resource(res);
+	}
+
 	kfree(info);
 }
 
diff --git a/include/linux/pci.h b/include/linux/pci.h
index b00f5f38f77d..ce724d067fd2 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -148,6 +148,13 @@ enum {
 	DEVICE_COUNT_RESOURCE = PCI_NUM_RESOURCES,
 };
 
+/*
+ * Max CXL HDM decoders tracked per endpoint in pci_dev->coh_resource[].
+ * CXL 3.1 spec section 8.2.4.20.1 - CXL HDM Decoder Capability Register,
+ * mention a max of 10 decoders for a CXL device.
+ */
+#define PCI_CXL_MAX_COHERENT_RANGES 10
+
 /**
  * enum pci_interrupt_pin - PCI INTx interrupt values
  * @PCI_INTERRUPT_UNKNOWN: Unknown or unassigned interrupt
@@ -572,6 +579,13 @@ struct pci_dev {
 #endif
 #ifdef CONFIG_CXL_RESET
 	struct cxl_hdm_info *hdm;	/* CXL HDM decoder state */
+	/*
+	 * Precommitted CXL HDM decoder coherent ranges, snapshotted before
+	 * any driver binds. One entry per decoder index. Only written by
+	 * pci_cxl_hdm_cache_init()/_release(), outside any bound driver's
+	 * read window.
+	 */
+	struct resource coh_resource[PCI_CXL_MAX_COHERENT_RANGES];
 #endif
 #ifdef CONFIG_PCI_NPEM
 	struct npem	*npem;		/* Native PCIe Enclosure Management */
-- 
2.43.0