[PATCH v7 10/11] PCI/cxl: Expose CXL Reset as a PCI reset method

[Srirangan Madhavan <smadhavan@nvidia.com>]

Add the CXL Reset helper to the PCI reset-method table so userspace can
select it through the existing reset_method ABI.

Advertise the method for Type 2 CXL devices that report CXL Reset support
in the CXL Device DVSEC. Reset execution still requires cached HDM decoder
state for the target and mem-capable siblings so that affected ranges can
be validated and HDM programming can be restored. If that state is
unavailable at reset time, return -ENOTTY so PCI can try the next reset
method.

Signed-off-by: Srirangan Madhavan <smadhavan@nvidia.com>
---
 drivers/cxl/core/reset.c | 33 +++++++++++++++++++++++++++++++++
 drivers/pci/pci.c        |  2 ++
 include/linux/pci.h      |  2 +-
 3 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/drivers/cxl/core/reset.c b/drivers/cxl/core/reset.c
index d801c91a5cbf..694d8a3789a4 100644
--- a/drivers/cxl/core/reset.c
+++ b/drivers/cxl/core/reset.c
@@ -1035,6 +1035,34 @@ static int cxl_reset_dvsec(struct pci_dev *pdev)
 	return dvsec;
 }
 
+static bool cxl_reset_hdm_available(struct pci_dev *pdev)
+{
+	struct cxl_hdm_info *info = READ_ONCE(pdev->hdm);
+
+	/*
+	 * pdev->hdm is allocated with PCI-device devres. Reset requests
+	 * operate on a live pci_dev, so the devres allocation remains valid
+	 * for this check.
+	 */
+	return info && info->regs.hdm_decoder;
+}
+
+static bool cxl_reset_scope_hdm_available(struct cxl_reset_context *ctx)
+{
+	if (!cxl_reset_hdm_available(ctx->target))
+		return false;
+
+	for (int i = 0; i < ctx->nr_siblings; i++) {
+		struct cxl_reset_sibling *sibling = &ctx->siblings[i];
+
+		if (sibling->has_mem &&
+		    !cxl_reset_hdm_available(sibling->pdev))
+			return false;
+	}
+
+	return true;
+}
+
 static int cxl_reset_update_ctrl2(struct pci_dev *pdev, int dvsec, u16 set,
 				  u16 clear)
 {
@@ -1211,6 +1239,11 @@ int cxl_reset_function(struct pci_dev *pdev, bool probe)
 	if (rc)
 		goto out;
 
+	if (!cxl_reset_scope_hdm_available(&ctx)) {
+		rc = -ENOTTY;
+		goto out;
+	}
+
 	rc = cxl_pci_functions_lock(&ctx);
 	if (rc)
 		goto out_unlock;
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 360f2aaee10c..b1ec20126390 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -33,6 +33,7 @@
 #include <asm/dma.h>
 #include <linux/aer.h>
 #include <linux/bitfield.h>
+#include <cxl/cxl.h>
 #include "pci.h"
 
 DEFINE_MUTEX(pci_slot_mutex);
@@ -5081,6 +5082,7 @@ const struct pci_reset_fn_method pci_reset_fn_methods[] = {
 	{ pci_dev_acpi_reset, .name = "acpi" },
 	{ pcie_reset_flr, .name = "flr" },
 	{ pci_af_flr, .name = "af_flr" },
+	{ cxl_reset_function, .name = "cxl_reset" },
 	{ pci_pm_reset, .name = "pm" },
 	{ pci_reset_bus_function, .name = "bus" },
 	{ cxl_reset_bus_function, .name = "cxl_bus" },
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 4df030837a3a..05b5feac5a49 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -51,7 +51,7 @@
 			       PCI_STATUS_PARITY)
 
 /* Number of reset methods used in pci_reset_fn_methods array in pci.c */
-#define PCI_NUM_RESET_METHODS 8
+#define PCI_NUM_RESET_METHODS 9
 
 #define PCI_RESET_PROBE		true
 #define PCI_RESET_DO_RESET	false
-- 
2.43.0