[PATCH V3 3/3] PCI: Add helpers to enable/disable CXL.mem and CXL.cache

From: Sean V Kelley
Date: Wed May 20 2020 - 14:06:53 EST


With these helpers, a device driver can enable/disable access to
CXL.mem and CXL.cache. Note that the device driver is responsible for
managing the memory area.

Signed-off-by: Sean V Kelley <sean.v.kelley@xxxxxxxxxxxxxxx>
---
drivers/pci/cxl.c | 84 +++++++++++++++++++++++++++++++++++++++++++++++
drivers/pci/pci.h | 8 +++++
2 files changed, 92 insertions(+)

diff --git a/drivers/pci/cxl.c b/drivers/pci/cxl.c
index 4497c597347f..e58e5262b59a 100644
--- a/drivers/pci/cxl.c
+++ b/drivers/pci/cxl.c
@@ -24,6 +24,90 @@
#define PCI_CXL_HDM_COUNT(reg) (((reg) & (3 << 4)) >> 4)
#define PCI_CXL_VIRAL BIT(14)

+#define PCI_CXL_CONFIG_LOCK BIT(0)
+
+static void pci_cxl_unlock(struct pci_dev *dev)
+{
+ int cxl = dev->cxl_cap;
+ u16 lock;
+
+ pci_read_config_word(dev, cxl + PCI_CXL_LOCK, &lock);
+ lock &= ~PCI_CXL_CONFIG_LOCK;
+ pci_write_config_word(dev, cxl + PCI_CXL_LOCK, lock);
+}
+
+static void pci_cxl_lock(struct pci_dev *dev)
+{
+ int cxl = dev->cxl_cap;
+ u16 lock;
+
+ pci_read_config_word(dev, cxl + PCI_CXL_LOCK, &lock);
+ lock |= PCI_CXL_CONFIG_LOCK;
+ pci_write_config_word(dev, cxl + PCI_CXL_LOCK, lock);
+}
+
+/*
+ * CXL DVSEC CTRL registers have Read-Write-Lockable attributes.
+ * PCI_CXL_CONFIG_LOCK locks these CTRL registers by making them RO.
+ * This lock prevents future changes to configuration and is not intended
+ * for enforcing mutual exclusion. See CXL 1.1, sec 7.1.1.6
+ */
+static int pci_cxl_enable_disable_feature(struct pci_dev *dev, int enable,
+ u16 feature)
+{
+ int cxl = dev->cxl_cap;
+ int ret;
+ u16 reg;
+
+ if (!dev->cxl_cap)
+ return -EINVAL;
+
+ /* Only for Device 0 Function 0, Root Complex Integrated Endpoints */
+ if (dev->devfn != 0 || (pci_pcie_type(dev) != PCI_EXP_TYPE_RC_END))
+ return -EINVAL;
+
+ pci_cxl_unlock(dev);
+ ret = pci_read_config_word(dev, cxl + PCI_CXL_CTRL, &reg);
+ if (ret)
+ goto lock;
+
+ if (enable)
+ reg |= feature;
+ else
+ reg &= ~feature;
+
+ ret = pci_write_config_word(dev, cxl + PCI_CXL_CTRL, reg);
+
+lock:
+ pci_cxl_lock(dev);
+
+ return ret;
+}
+
+int pci_cxl_mem_enable(struct pci_dev *dev)
+{
+ return pci_cxl_enable_disable_feature(dev, true, PCI_CXL_MEM);
+}
+EXPORT_SYMBOL_GPL(pci_cxl_mem_enable);
+
+void pci_cxl_mem_disable(struct pci_dev *dev)
+{
+ pci_cxl_enable_disable_feature(dev, false, PCI_CXL_MEM);
+}
+EXPORT_SYMBOL_GPL(pci_cxl_mem_disable);
+
+int pci_cxl_cache_enable(struct pci_dev *dev)
+{
+ return pci_cxl_enable_disable_feature(dev, true, PCI_CXL_CACHE);
+}
+EXPORT_SYMBOL_GPL(pci_cxl_cache_enable);
+
+void pci_cxl_cache_disable(struct pci_dev *dev)
+{
+ pci_cxl_enable_disable_feature(dev, false, PCI_CXL_CACHE);
+}
+EXPORT_SYMBOL_GPL(pci_cxl_cache_disable);
+
/*
* pci_find_cxl_capability - Identify and return offset to Vendor-Specific
* capabilities.
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index d9905e2dee95..5ec7fa0eb709 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -472,8 +472,16 @@ static inline void pci_restore_ats_state(struct pci_dev *dev) { }
#ifdef CONFIG_PCI_CXL
/* Compute eXpress Link */
void pci_cxl_init(struct pci_dev *dev);
+int pci_cxl_mem_enable(struct pci_dev *dev);
+void pci_cxl_mem_disable(struct pci_dev *dev);
+int pci_cxl_cache_enable(struct pci_dev *dev);
+void pci_cxl_cache_disable(struct pci_dev *dev);
#else
static inline void pci_cxl_init(struct pci_dev *dev) { }
+static inline int pci_cxl_mem_enable(struct pci_dev *dev) { return 0; }
+static inline void pci_cxl_mem_disable(struct pci_dev *dev) { }
+static inline int pci_cxl_cache_enable(struct pci_dev *dev) { return 0; }
+static inline void pci_cxl_cache_disable(struct pci_dev *dev) { }
#endif

#ifdef CONFIG_PCI_PRI
--
2.26.2