[PATCH v11 12/12] PCI/CXL: Restore HDM state after CXL bus reset

[Srirangan Madhavan <smadhavan@nvidia.com>]

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

Restore PCI config state first so BARs are valid before HDM MMIO access.
If HDM restore fails, save a disabled PCI command state so later PCI
restore does not reopen bus mastering over invalid decoder state.

Reject cxl_bus reset for multifunction devices, matching cxl_reset.

This restores only HDM component decoder state. It does not restore CXL
Device DVSEC range/control registers.

Reported-by: Alex Williamson <alex.williamson@redhat.com>
Tested-by: Richard Cheng <icheng@nvidia.com>
Signed-off-by: Srirangan Madhavan <smadhavan@nvidia.com>
---
 drivers/cxl/core/resource.c | 18 ++++++++++++++++++
 drivers/pci/pci.c           |  6 ++++++
 include/cxl/cxl.h           |  6 ++++++
 3 files changed, 30 insertions(+)

diff --git a/drivers/cxl/core/resource.c b/drivers/cxl/core/resource.c
index fe330b825c0b..92d56d8baeb9 100644
--- a/drivers/cxl/core/resource.c
+++ b/drivers/cxl/core/resource.c
@@ -850,6 +850,24 @@ static int cxl_pci_target_reset_prepare(struct pci_dev *pdev,
 	return 0;
 }
 
+int cxl_restore_hdm_after_pci_reset(struct pci_dev *pdev)
+{
+	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_hdm(pdev);
+	if (rc) {
+		cxl_reset_save_disabled_state(pdev);
+		return rc;
+	}
+
+	return cxl_reset_save_restored_state(pdev, command);
+}
+
 static void cxl_hdm_range_context_init(struct cxl_hdm_range_context *ctx)
 {
 	INIT_LIST_HEAD(&ctx->ranges);
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 157f06c576e9..0a3ffdc70466 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -5027,6 +5027,9 @@ static int cxl_reset_bus_function(struct pci_dev *dev, bool probe)
 	if (!dvsec)
 		return -ENOTTY;
 
+	if (dev->multifunction)
+		return -ENOTTY;
+
 	if (probe)
 		return 0;
 
@@ -5054,6 +5057,9 @@ 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)
+		rc = cxl_restore_hdm_after_pci_reset(dev);
+
 	pci_dev_reset_iommu_done(dev);
 	return rc;
 }
diff --git a/include/cxl/cxl.h b/include/cxl/cxl.h
index d07afb789d63..c8b12f50f71c 100644
--- a/include/cxl/cxl.h
+++ b/include/cxl/cxl.h
@@ -162,6 +162,7 @@ struct cxl_hdm_info {
 #ifdef CONFIG_CXL_RESET
 void pci_cxl_hdm_init(struct pci_dev *pdev);
 void pci_cxl_hdm_release(struct pci_dev *pdev);
+int cxl_restore_hdm_after_pci_reset(struct pci_dev *pdev);
 int cxl_reset_function(struct pci_dev *pdev, bool probe);
 #else
 static inline void pci_cxl_hdm_init(struct pci_dev *pdev)
@@ -172,6 +173,11 @@ static inline void pci_cxl_hdm_release(struct pci_dev *pdev)
 {
 }
 
+static inline int cxl_restore_hdm_after_pci_reset(struct pci_dev *pdev)
+{
+	return 0;
+}
+
 static inline int cxl_reset_function(struct pci_dev *pdev, bool probe)
 {
 	return -ENOTTY;
-- 
2.43.0