[PATCH v13 10/15] cxl: Add CXL Device Reset sequencing

[Srirangan Madhavan <smadhavan@nvidia.com>]

Implement CXL Device Reset for eligible Type 2 devices: disable CXL.cache,
perform supported writeback, drain transactions, prepare the IOMMU,
initiate reset with Memory Clear enabled, and wait for completion.

Observe the 100 ms post-reset quiet period before polling Status2, and
treat an all-ones read as not ready. Treat Control2 command bits as
transient state, restore cache policy on exit, preserve the primary error,
and abort when IOMMU preparation fails.

Signed-off-by: Srirangan Madhavan <smadhavan@nvidia.com>
---
 drivers/cxl/core/resource.c   | 229 ++++++++++++++++++++++++++++++++++
 include/cxl/cxl.h             |   7 ++
 include/uapi/linux/pci_regs.h |  14 +++
 3 files changed, 250 insertions(+)

diff --git a/drivers/cxl/core/resource.c b/drivers/cxl/core/resource.c
index b5f8c28e613f..57eec77cbb21 100644
--- a/drivers/cxl/core/resource.c
+++ b/drivers/cxl/core/resource.c
@@ -8,6 +8,8 @@
 #include <linux/export.h>
 #include <linux/io.h>
 #include <linux/ioport.h>
+#include <linux/iommu.h>
+#include <linux/jiffies.h>
 #include <linux/kernel.h>
 #include <linux/pci.h>
 #include <linux/slab.h>
@@ -419,3 +421,230 @@ void pci_cxl_hdm_cache_release(struct pci_dev *pdev)
 	pdev->hdm = NULL;
 	kfree(info);
 }
+
+/*
+ * 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
+ * initiating CXL Reset, then limits software to CXL Status2 access until
+ * reset completion, timeout, or error.
+ */
+#define CXL_RESET_RRS_WAIT_MS 100
+#define CXL_RESET_STATUS_POLL_MS 20
+static const u32 cxl_reset_timeout_ms[] = {
+	10, 100, 1000, 10000, 100000,
+};
+
+#define CXL_CACHE_WBI_TIMEOUT_US 100000
+#define CXL_CACHE_WBI_POLL_US 100
+
+#define CXL_RESET_CTRL2_CMD_MASK \
+	(PCI_DVSEC_CXL_INIT_CACHE_WBI | PCI_DVSEC_CXL_INIT_CXL_RST)
+
+static int cxl_reset_update_ctrl2_no_replay(struct pci_dev *pdev, int dvsec,
+					    u16 set, u16 clear)
+{
+	u16 ctrl2;
+	int rc;
+
+	rc = pci_read_config_word(pdev, dvsec + PCI_DVSEC_CXL_CTRL2, &ctrl2);
+	if (rc)
+		return pcibios_err_to_errno(rc);
+	if (PCI_POSSIBLE_ERROR(ctrl2))
+		return -ENODEV;
+
+	/*
+	 * INIT_CACHE_WBI and INIT_CXL_RST are commands. Do not replay a command
+	 * that remains set in the value read back while updating persistent
+	 * Control2 state.
+	 */
+	ctrl2 &= ~CXL_RESET_CTRL2_CMD_MASK;
+	ctrl2 &= ~clear;
+	ctrl2 |= set;
+
+	rc = pci_write_config_word(pdev, dvsec + PCI_DVSEC_CXL_CTRL2, ctrl2);
+	if (rc)
+		return pcibios_err_to_errno(rc);
+
+	return 0;
+}
+
+static int cxl_reset_wait_cache_wbi(struct pci_dev *pdev, int dvsec)
+{
+	unsigned long deadline;
+	u16 status2;
+	int rc;
+
+	rc = cxl_reset_update_ctrl2_no_replay(pdev, dvsec,
+					      PCI_DVSEC_CXL_INIT_CACHE_WBI, 0);
+	if (rc)
+		return rc;
+
+	deadline = jiffies + usecs_to_jiffies(CXL_CACHE_WBI_TIMEOUT_US);
+	while (time_before(jiffies, deadline)) {
+		usleep_range(CXL_CACHE_WBI_POLL_US,
+			     CXL_CACHE_WBI_POLL_US * 2);
+
+		rc = pci_read_config_word(pdev, dvsec + PCI_DVSEC_CXL_STATUS2,
+					  &status2);
+		if (rc)
+			return pcibios_err_to_errno(rc);
+		if (PCI_POSSIBLE_ERROR(status2))
+			return -ENODEV;
+		if (status2 & PCI_DVSEC_CXL_CACHE_INV)
+			return 0;
+	}
+
+	/* Do not miss completion concurrent with the polling deadline. */
+	rc = pci_read_config_word(pdev, dvsec + PCI_DVSEC_CXL_STATUS2,
+				  &status2);
+	if (rc)
+		return pcibios_err_to_errno(rc);
+	if (PCI_POSSIBLE_ERROR(status2))
+		return -ENODEV;
+	if (status2 & PCI_DVSEC_CXL_CACHE_INV)
+		return 0;
+
+	return -ETIMEDOUT;
+}
+
+static int cxl_reset_disable_cache(struct pci_dev *pdev, int dvsec, u16 cap)
+{
+	int rc;
+
+	rc = cxl_reset_update_ctrl2_no_replay(pdev, dvsec,
+					      PCI_DVSEC_CXL_DISABLE_CACHING, 0);
+	if (rc || !(cap & PCI_DVSEC_CXL_CACHE_WBI_CAPABLE))
+		return rc;
+
+	return cxl_reset_wait_cache_wbi(pdev, dvsec);
+}
+
+static int cxl_reset_wait_done(struct pci_dev *pdev, int dvsec, u16 cap)
+{
+	unsigned long deadline;
+	u32 timeout_ms;
+	u16 status2;
+	int idx, rc;
+
+	idx = FIELD_GET(PCI_DVSEC_CXL_RST_TIMEOUT, cap);
+	if (idx >= ARRAY_SIZE(cxl_reset_timeout_ms)) {
+		int last = ARRAY_SIZE(cxl_reset_timeout_ms) - 1;
+
+		pci_warn(pdev,
+			 "unknown CXL reset timeout encoding %d; using %u ms\n",
+			 idx, cxl_reset_timeout_ms[last]);
+		idx = last;
+	}
+
+	timeout_ms = max_t(u32, cxl_reset_timeout_ms[idx],
+			   CXL_RESET_RRS_WAIT_MS);
+	msleep(CXL_RESET_RRS_WAIT_MS);
+	deadline = jiffies + msecs_to_jiffies(timeout_ms -
+					      CXL_RESET_RRS_WAIT_MS);
+
+	for (;;) {
+		rc = pci_read_config_word(pdev, dvsec + PCI_DVSEC_CXL_STATUS2,
+					  &status2);
+		if (rc || status2 == U16_MAX)
+			goto not_ready;
+		if (status2 & PCI_DVSEC_CXL_RST_ERR)
+			return -EIO;
+		if (status2 & PCI_DVSEC_CXL_RST_DONE)
+			return 0;
+
+not_ready:
+		if (time_after_eq(jiffies, deadline))
+			return -ETIMEDOUT;
+
+		msleep(CXL_RESET_STATUS_POLL_MS);
+	}
+}
+
+static int cxl_reset_execute(struct pci_dev *pdev, int dvsec, u16 cap)
+{
+	int rc, rc2;
+
+	rc = cxl_reset_disable_cache(pdev, dvsec, cap);
+	if (rc)
+		goto out_enable_cache;
+
+	if (!pci_wait_for_pending_transaction(pdev)) {
+		pci_err(pdev, "timed out waiting for pending transactions\n");
+		rc = -ETIMEDOUT;
+		goto out_enable_cache;
+	}
+
+	rc = pci_dev_reset_iommu_prepare(pdev);
+	if (rc) {
+		pci_err(pdev, "failed to stop IOMMU for CXL reset: %d\n", rc);
+		goto out_enable_cache;
+	}
+
+	/* Clear Memory Clear again even if this command write reports failure. */
+	rc = cxl_reset_update_ctrl2_no_replay(pdev, dvsec,
+					      PCI_DVSEC_CXL_INIT_CXL_RST |
+					      PCI_DVSEC_CXL_RST_MEM_CLR_EN, 0);
+	if (rc)
+		goto out_clear_memory;
+
+	rc = cxl_reset_wait_done(pdev, dvsec, cap);
+
+out_clear_memory:
+	rc2 = cxl_reset_update_ctrl2_no_replay(
+		pdev, dvsec, 0, PCI_DVSEC_CXL_RST_MEM_CLR_EN);
+	if (rc2)
+		pci_err(pdev, "failed to clear CXL Reset Memory Clear: %d\n",
+			rc2);
+	rc = rc ?: rc2;
+
+	pci_dev_reset_iommu_done(pdev);
+
+out_enable_cache:
+	/*
+	 * DISABLE_CACHING was the first preparation step. Restore the original
+	 * cache policy last, after reset exclusion has ended.
+	 */
+	rc2 = cxl_reset_update_ctrl2_no_replay(
+		pdev, dvsec, 0, PCI_DVSEC_CXL_DISABLE_CACHING);
+	if (rc2)
+		pci_err(pdev, "failed to re-enable CXL caching: %d\n", rc2);
+	rc = rc ?: rc2;
+
+	return rc;
+}
+
+int cxl_reset_function(struct pci_dev *pdev, bool probe)
+{
+	int dvsec, rc;
+	u16 cap, ctrl;
+
+	dvsec = pci_find_dvsec_capability(pdev, PCI_VENDOR_ID_CXL,
+					  PCI_DVSEC_CXL_DEVICE);
+	if (!dvsec)
+		return -ENOTTY;
+
+	rc = pci_read_config_word(pdev, dvsec + PCI_DVSEC_CXL_CAP, &cap);
+	if (rc)
+		return pcibios_err_to_errno(rc);
+	if (PCI_POSSIBLE_ERROR(cap))
+		return -ENODEV;
+	if (!(cap & PCI_DVSEC_CXL_CACHE_CAPABLE) ||
+	    !(cap & PCI_DVSEC_CXL_MEM_CAPABLE) ||
+	    !(cap & PCI_DVSEC_CXL_RST_CAPABLE) ||
+	    !(cap & PCI_DVSEC_CXL_RST_MEM_CLR_CAPABLE))
+		return -ENOTTY;
+
+	rc = pci_read_config_word(pdev, dvsec + PCI_DVSEC_CXL_CTRL, &ctrl);
+	if (rc)
+		return pcibios_err_to_errno(rc);
+	if (PCI_POSSIBLE_ERROR(ctrl))
+		return -ENODEV;
+	if (!(ctrl & PCI_DVSEC_CXL_CACHE_ENABLE) ||
+	    !(ctrl & PCI_DVSEC_CXL_MEM_ENABLE))
+		return -ENOTTY;
+
+	if (probe)
+		return 0;
+
+	return cxl_reset_execute(pdev, dvsec, cap);
+}
diff --git a/include/cxl/cxl.h b/include/cxl/cxl.h
index 4bad41e74f74..a07dbf7463c0 100644
--- a/include/cxl/cxl.h
+++ b/include/cxl/cxl.h
@@ -6,6 +6,7 @@
 #define __CXL_CXL_H__
 
 #include <linux/device.h>
+#include <linux/errno.h>
 #include <linux/node.h>
 #include <linux/ioport.h>
 #include <linux/range.h>
@@ -201,6 +202,7 @@ 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_reset_function(struct pci_dev *pdev, bool probe);
 #else
 static inline void pci_cxl_hdm_cache_init(struct pci_dev *pdev)
 {
@@ -209,6 +211,11 @@ static inline void pci_cxl_hdm_cache_init(struct pci_dev *pdev)
 static inline void pci_cxl_hdm_cache_release(struct pci_dev *pdev)
 {
 }
+
+static inline int cxl_reset_function(struct pci_dev *pdev, bool probe)
+{
+	return -ENOTTY;
+}
 #endif
 
 /**
diff --git a/include/uapi/linux/pci_regs.h b/include/uapi/linux/pci_regs.h
index facaa324bd86..7224857c7b30 100644
--- a/include/uapi/linux/pci_regs.h
+++ b/include/uapi/linux/pci_regs.h
@@ -1352,8 +1352,22 @@
 #define   PCI_DVSEC_CXL_CACHE_CAPABLE			_BITUL(0)
 #define   PCI_DVSEC_CXL_MEM_CAPABLE			_BITUL(2)
 #define   PCI_DVSEC_CXL_HDM_COUNT			__GENMASK(5, 4)
+#define   PCI_DVSEC_CXL_CACHE_WBI_CAPABLE		_BITUL(6)
+#define   PCI_DVSEC_CXL_RST_CAPABLE			_BITUL(7)
+#define   PCI_DVSEC_CXL_RST_TIMEOUT			__GENMASK(10, 8)
+#define   PCI_DVSEC_CXL_RST_MEM_CLR_CAPABLE		_BITUL(11)
 #define  PCI_DVSEC_CXL_CTRL				0xC
+#define   PCI_DVSEC_CXL_CACHE_ENABLE			_BITUL(0)
 #define   PCI_DVSEC_CXL_MEM_ENABLE			_BITUL(2)
+#define  PCI_DVSEC_CXL_CTRL2				0x10
+#define   PCI_DVSEC_CXL_DISABLE_CACHING			_BITUL(0)
+#define   PCI_DVSEC_CXL_INIT_CACHE_WBI			_BITUL(1)
+#define   PCI_DVSEC_CXL_INIT_CXL_RST			_BITUL(2)
+#define   PCI_DVSEC_CXL_RST_MEM_CLR_EN			_BITUL(3)
+#define  PCI_DVSEC_CXL_STATUS2				0x12
+#define   PCI_DVSEC_CXL_CACHE_INV			_BITUL(0)
+#define   PCI_DVSEC_CXL_RST_DONE			_BITUL(1)
+#define   PCI_DVSEC_CXL_RST_ERR				_BITUL(2)
 #define  PCI_DVSEC_CXL_RANGE_SIZE_HIGH(i)		(0x18 + (i * 0x10))
 #define  PCI_DVSEC_CXL_RANGE_SIZE_LOW(i)		(0x1C + (i * 0x10))
 #define   PCI_DVSEC_CXL_MEM_INFO_VALID			_BITUL(0)
-- 
2.43.0