From: Srirangan Madhavan <smadhavan@nvidia.com>
To: Alison Schofield <alison.schofield@intel.com>,
Bjorn Helgaas <bhelgaas@google.com>,
Dave Jiang <dave.jiang@intel.com>,
Davidlohr Bueso <dave@stgolabs.net>,
Ira Weiny <ira.weiny@intel.com>,
Jonathan Cameron <jic23@kernel.org>,
Vishal Verma <vishal.l.verma@intel.com>,
linux-cxl@vger.kernel.org, linux-pci@vger.kernel.org,
linux-kernel@vger.kernel.org
Cc: Alex Williamson <alex.williamson@redhat.com>,
vsethi@nvidia.com, alwilliamson@nvidia.com,
Sai Yashwanth Reddy Kancherla <skancherla@nvidia.com>,
Vishal Aslot <vaslot@nvidia.com>,
Manish Honap <mhonap@nvidia.com>, Jiandi An <jan@nvidia.com>,
Richard Cheng <icheng@nvidia.com>,
linux-tegra@vger.kernel.org,
Srirangan Madhavan <smadhavan@nvidia.com>
Subject: [PATCH v15 10/16] PCI/CXL: Add CXL Device Reset sequencing
Date: Sun, 11 Oct 2026 02:14:16 +0000 [thread overview]
Message-ID: <20261011021422.3428136-11-smadhavan@nvidia.com> (raw)
In-Reply-To: <20261011021422.3428136-1-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.
Reuse Device DVSEC discovery from cache initialization and keep the
reset entry point declaration private to PCI core.
Link: https://git.kernel.org/pub/scm/linux/kernel/git/djiang/linux.git/commit/?id=04f8f84816d724f8b47f4d47a77916ac37c63a49
Suggested-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Srirangan Madhavan <smadhavan@nvidia.com>
---
drivers/pci/cxl.c | 249 +++++++++++++++++++++++++++++++++-
drivers/pci/pci.h | 5 +
include/uapi/linux/pci_regs.h | 14 ++
3 files changed, 267 insertions(+), 1 deletion(-)
diff --git a/drivers/pci/cxl.c b/drivers/pci/cxl.c
index 471b57391593..9eb13adf0daa 100644
--- a/drivers/pci/cxl.c
+++ b/drivers/pci/cxl.c
@@ -3,13 +3,17 @@
/*
* CXL reset support in the PCI core. Cache the HDM decoder state of a CXL
* memory device at enumeration, so it can be restored after a reset without
- * a CXL driver. HDM register formats and programming live in drivers/cxl.
+ * a CXL driver, and implement CXL Device Reset. HDM register formats and
+ * programming live in drivers/cxl.
*/
#include <linux/bitfield.h>
#include <linux/cleanup.h>
+#include <linux/delay.h>
#include <linux/errno.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>
@@ -221,3 +225,246 @@ void pci_cxl_hdm_cache_release(struct pci_dev *pdev)
{
cxl_hdm_cache_release(&pdev->hdm);
}
+
+/*
+ * 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
+#define CXL_RESET_MAX_WAIT_MS 20000
+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_restore_cache_policy(struct pci_dev *pdev, int dvsec,
+ u16 saved_ctrl2)
+{
+ int rc;
+
+ rc = cxl_reset_update_ctrl2_no_replay(pdev, dvsec,
+ saved_ctrl2 & PCI_DVSEC_CXL_DISABLE_CACHING,
+ PCI_DVSEC_CXL_DISABLE_CACHING);
+ if (rc)
+ pci_err(pdev, "failed to restore CXL cache policy: %d\n", rc);
+
+ return rc;
+}
+
+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)) {
+ pci_warn(pdev,
+ "unknown CXL reset timeout encoding %d; using %u ms\n",
+ idx, CXL_RESET_MAX_WAIT_MS);
+ idx = ARRAY_SIZE(cxl_reset_timeout_ms) - 1;
+ }
+
+ /* Allow one retry after the mandatory 100 ms quiet period. */
+ timeout_ms = clamp_t(u32, cxl_reset_timeout_ms[idx],
+ CXL_RESET_RRS_WAIT_MS + CXL_RESET_STATUS_POLL_MS,
+ CXL_RESET_MAX_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)
+ return pcibios_err_to_errno(rc);
+ if (status2 != U16_MAX) {
+ if (status2 & PCI_DVSEC_CXL_RST_ERR)
+ return -EIO;
+ if (status2 & PCI_DVSEC_CXL_RST_DONE)
+ return 0;
+ }
+
+ if (time_after_eq(jiffies, deadline))
+ return -ETIMEDOUT;
+
+ msleep(CXL_RESET_STATUS_POLL_MS);
+ }
+}
+
+static int cxl_clear_memory(struct pci_dev *pdev, int dvsec, bool initiate)
+{
+ if (initiate)
+ return cxl_reset_update_ctrl2_no_replay(pdev, dvsec,
+ PCI_DVSEC_CXL_INIT_CXL_RST |
+ PCI_DVSEC_CXL_RST_MEM_CLR_EN,
+ 0);
+
+ return cxl_reset_update_ctrl2_no_replay(pdev, dvsec, 0,
+ PCI_DVSEC_CXL_RST_MEM_CLR_EN);
+}
+
+static int __cxl_reset_execute(struct pci_dev *pdev, int dvsec, u16 cap)
+{
+ int rc, rc2;
+
+ if (!pci_wait_for_pending_transaction(pdev)) {
+ pci_err(pdev, "timed out waiting for pending transactions\n");
+ return -ETIMEDOUT;
+ }
+
+ rc = pci_dev_reset_iommu_prepare(pdev);
+ if (rc) {
+ pci_err(pdev, "failed to stop IOMMU for CXL reset: %d\n", rc);
+ return rc;
+ }
+
+ rc = cxl_clear_memory(pdev, dvsec, true);
+ if (!rc)
+ rc = cxl_reset_wait_done(pdev, dvsec, cap);
+
+ /* Always clear Memory Clear; successful cleanup must not hide reset failure. */
+ rc2 = cxl_clear_memory(pdev, dvsec, false);
+ if (rc2)
+ pci_err(pdev, "failed to clear CXL Reset Memory Clear: %d\n", rc2);
+ rc = rc ?: rc2;
+
+ pci_dev_reset_iommu_done(pdev);
+ return rc;
+}
+
+static int cxl_reset_execute(struct pci_dev *pdev, int dvsec, u16 cap)
+{
+ u16 saved_ctrl2;
+ int rc, rc2;
+
+ rc = pci_read_config_word(pdev, dvsec + PCI_DVSEC_CXL_CTRL2, &saved_ctrl2);
+ if (rc)
+ return pcibios_err_to_errno(rc);
+ if (PCI_POSSIBLE_ERROR(saved_ctrl2))
+ return -ENODEV;
+
+ rc = cxl_reset_disable_cache(pdev, dvsec, cap);
+ if (!rc)
+ rc = __cxl_reset_execute(pdev, dvsec, cap);
+ /* Restore cache policy after any attempt to disable caching. */
+ rc2 = cxl_reset_restore_cache_policy(pdev, dvsec, saved_ctrl2);
+ return rc ?: rc2;
+}
+
+int cxl_reset_function(struct pci_dev *pdev, bool probe)
+{
+ u16 dvsec, cap, ctrl;
+ int rc;
+
+ rc = cxl_pci_device_dvsec(pdev, &dvsec, &cap);
+ if (rc)
+ return rc;
+ 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/drivers/pci/pci.h b/drivers/pci/pci.h
index 9e218f236e66..743e65abd758 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -733,9 +733,14 @@ static inline void pci_doe_disconnected(struct pci_dev *pdev) { }
#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) { }
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
#ifdef CONFIG_PCI_NPEM
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
next prev parent reply other threads:[~2026-10-11 2:15 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-11 2:14 [PATCH v15 00/16] PCI/CXL: Add CXL reset support for Type 2 devices Srirangan Madhavan
2026-10-11 2:14 ` [PATCH v15 01/16] cxl: Drop stale decoder interleave limit comment Srirangan Madhavan
2026-10-11 2:14 ` [PATCH v15 02/16] cxl: Share CXL port upstream PCI device lookup Srirangan Madhavan
2026-10-11 2:14 ` [PATCH v15 03/16] cxl: Move decoder declarations to shared header Srirangan Madhavan
2026-10-11 2:14 ` [PATCH v15 04/16] cxl: Embed decoder configuration in a standalone structure Srirangan Madhavan
2026-10-11 2:14 ` [PATCH v15 05/16] cxl: Introduce endpoint HDM decoder settings Srirangan Madhavan
2026-10-11 2:14 ` [PATCH v15 06/16] cxl: Move HDM decoder helpers to built-in code Srirangan Madhavan
2026-10-11 2:14 ` [PATCH v15 07/16] cxl: Share HDM decoder register unpacking Srirangan Madhavan
2026-10-11 2:14 ` [PATCH v15 08/16] cxl: Refresh cached PCI HDM decoder settings Srirangan Madhavan
2026-10-11 2:14 ` [PATCH v15 09/16] PCI/CXL: Cache endpoint HDM state during PCI enumeration Srirangan Madhavan
2026-10-11 2:14 ` Srirangan Madhavan [this message]
2026-10-11 2:14 ` [PATCH v15 11/16] cxl: Validate and synchronize HDM ranges around reset Srirangan Madhavan
2026-10-11 2:14 ` [PATCH v15 12/16] PCI/CXL: Reject reset with unsafe function scope Srirangan Madhavan
2026-10-11 2:14 ` [PATCH v15 13/16] PCI/CXL: Restore CXL state after PCI reset Srirangan Madhavan
2026-10-11 2:14 ` [PATCH v15 14/16] PCI/CXL: Expose CXL Reset as a PCI reset method Srirangan Madhavan
2026-10-11 2:14 ` [PATCH v15 15/16] PCI/CXL: Restore CXL state after CXL bus reset Srirangan Madhavan
2026-10-11 2:14 ` [PATCH v15 16/16] tools/testing/cxl: Add HDM decoder range checks Srirangan Madhavan
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