[PATCH v13 15/15] PCI/CXL: Restore CXL state after CXL bus reset

[Srirangan Madhavan <smadhavan@nvidia.com>]

CXL bus reset can clear HDM decoder programming and CXL Device DVSEC
control state. Restore the cached state after a successful cxl_bus reset
while IOMMU exclusion remains active.

Restore PCI configuration first so HDM MMIO is accessible, and preserve a
disabled state if restoration fails.

Tested-by: Richard Cheng <icheng@nvidia.com>
Signed-off-by: Srirangan Madhavan <smadhavan@nvidia.com>
---
 drivers/cxl/core/resource.c | 23 +++++++++++++++++++++--
 drivers/pci/pci.c           |  8 ++++++++
 include/cxl/cxl.h           | 17 +++++++++++++++++
 3 files changed, 46 insertions(+), 2 deletions(-)

diff --git a/drivers/cxl/core/resource.c b/drivers/cxl/core/resource.c
index 6bf503e498e1..0af0f96d5526 100644
--- a/drivers/cxl/core/resource.c
+++ b/drivers/cxl/core/resource.c
@@ -601,12 +601,12 @@ static int cxl_restore_hdm_decoder(struct pci_dev *pdev, void __iomem *hdm,
 	return 0;
 }
 
-static int cxl_snapshot_hdm(struct pci_dev *pdev,
-			    struct cxl_hdm_info **snapshot)
+int cxl_snapshot_hdm(struct pci_dev *pdev, struct cxl_hdm_info **snapshot)
 {
 	struct cxl_hdm_info *info;
 	size_t size;
 
+	device_lock_assert(&pdev->dev);
 	guard(rwsem_read)(&cxl_rwsem.dpa);
 	info = pdev->hdm;
 	if (!info)
@@ -762,6 +762,25 @@ static int cxl_reset_save_restored_state(struct pci_dev *pdev, u16 command)
 	return rc;
 }
 
+int cxl_restore_state_after_pci_reset(struct pci_dev *pdev,
+				      struct cxl_hdm_info *snapshot)
+{
+	u16 command;
+	int rc;
+
+	device_lock_assert(&pdev->dev);
+	guard(rwsem_write)(&cxl_rwsem.region);
+
+	cxl_restore_pci_state_for_hdm_restore(pdev, &command);
+	rc = cxl_restore_state(pdev, snapshot);
+	if (rc) {
+		cxl_reset_save_disabled_state(pdev);
+		return rc;
+	}
+
+	return cxl_reset_save_restored_state(pdev, command);
+}
+
 /*
  * CXL r4.0 sec 9.7.2 defines the reset completion timeout encodings.
  * Sec 9.7.3 leaves config-space access behavior undefined for 100 ms after
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index dc57a202c91f..6928c99aa785 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -5015,6 +5015,7 @@ static int pci_reset_bus_function(struct pci_dev *dev, bool probe)
 
 static int cxl_reset_bus_function(struct pci_dev *dev, bool probe)
 {
+	struct cxl_hdm_info *snapshot __free(kfree) = NULL;
 	struct pci_dev *bridge;
 	u16 dvsec, reg, val;
 	int rc;
@@ -5037,6 +5038,10 @@ static int cxl_reset_bus_function(struct pci_dev *dev, bool probe)
 	if (rc)
 		return -ENOTTY;
 
+	rc = cxl_snapshot_hdm(dev, &snapshot);
+	if (rc && rc != -ENXIO)
+		return rc;
+
 	rc = pci_dev_reset_iommu_prepare(dev);
 	if (rc) {
 		pci_err(dev, "failed to stop IOMMU for a PCI reset: %d\n", rc);
@@ -5057,6 +5062,9 @@ static int cxl_reset_bus_function(struct pci_dev *dev, bool probe)
 		pci_write_config_word(bridge, dvsec + PCI_DVSEC_CXL_PORT_CTL,
 				      reg);
 
+	if (!rc && snapshot)
+		rc = cxl_restore_state_after_pci_reset(dev, snapshot);
+
 	pci_dev_reset_iommu_done(dev);
 	return rc;
 }
diff --git a/include/cxl/cxl.h b/include/cxl/cxl.h
index a07dbf7463c0..2ff5bb117942 100644
--- a/include/cxl/cxl.h
+++ b/include/cxl/cxl.h
@@ -202,6 +202,9 @@ struct cxl_register_map {
 #ifdef CONFIG_CXL_RESET
 void pci_cxl_hdm_cache_init(struct pci_dev *pdev);
 void pci_cxl_hdm_cache_release(struct pci_dev *pdev);
+int cxl_snapshot_hdm(struct pci_dev *pdev, struct cxl_hdm_info **snapshot);
+int cxl_restore_state_after_pci_reset(struct pci_dev *pdev,
+				      struct cxl_hdm_info *snapshot);
 int cxl_reset_function(struct pci_dev *pdev, bool probe);
 #else
 static inline void pci_cxl_hdm_cache_init(struct pci_dev *pdev)
@@ -212,6 +215,20 @@ static inline void pci_cxl_hdm_cache_release(struct pci_dev *pdev)
 {
 }
 
+static inline int cxl_snapshot_hdm(struct pci_dev *pdev,
+				   struct cxl_hdm_info **snapshot)
+{
+	*snapshot = NULL;
+	return -ENXIO;
+}
+
+static inline int
+cxl_restore_state_after_pci_reset(struct pci_dev *pdev,
+				  struct cxl_hdm_info *snapshot)
+{
+	return 0;
+}
+
 static inline int cxl_reset_function(struct pci_dev *pdev, bool probe)
 {
 	return -ENOTTY;
-- 
2.43.0