Latency tolerance reporting allows devices to send messages to the root
complex indicating their latency tolerance for snooped & unsnooped
memory transactions. Add support for enabling & disabling this
feature, along with a routine to set the max latencies a device should
send upstream.
Signed-off-by: Jesse Barnes <jbarnes@xxxxxxxxxxxxxxxx>
---
drivers/pci/pci.c | 149 ++++++++++++++++++++++++++++++++++++++++++++++
include/linux/pci.h | 5 ++
include/linux/pci_regs.h | 9 +++
3 files changed, 163 insertions(+), 0 deletions(-)
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 01e4cab..53302cb 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -1979,6 +1979,155 @@ void pci_disable_obff(struct pci_dev *dev)
}
EXPORT_SYMBOL(pci_disable_obff);
+/**
+ * pci_ltr_supported - check whether a device supports LTR
+ * @dev: PCI device
+ *
+ * RETURNS:
+ * True if @dev supports latency tolerance reporting, false otherwise.
+ */
+bool pci_ltr_supported(struct pci_dev *dev)
+{
+ int pos;
+ u32 cap;
+
+ if (!pci_is_pcie(dev))
+ return false;
+
+ pos = pci_pcie_cap(dev);
+ if (!pos)
+ return false;
+
+ pci_read_config_dword(dev, pos + PCI_EXP_DEVCAP2, &cap);
+
+ return cap & PCI_EXP_DEVCAP2_LTR;
+}
+EXPORT_SYMBOL(pci_ltr_supported);
+
+/**
+ * pci_enable_ltr - enable latency tolerance reporting
+ * @dev: PCI device
+ *
+ * Enable LTR on @dev if possible, which means enabling it first on
+ * upstream ports.
+ *
+ * RETURNS:
+ * Zero on success, errno on failure.
+ */
+int pci_enable_ltr(struct pci_dev *dev)
+{
+ int pos;
+ u16 ctrl;
+ int ret;
+
+ if (!pci_ltr_supported(dev))
+ return -ENOTSUPP;
+
+ pos = pci_pcie_cap(dev);
+ if (!pos)
+ return -ENOTSUPP;
+
+ /* Only primary function can enable/disable LTR */
+ if (PCI_FUNC(dev->devfn) != 0)
+ return -EINVAL;
+
+ /* Enable upstream ports first */
+ if (dev->bus) {
+ ret = pci_enable_ltr(dev->bus->self);
+ if (ret)
+ return ret;
+ }
+
+ pci_read_config_word(dev, pos + PCI_EXP_DEVCTL2, &ctrl);
+ ctrl |= PCI_EXP_LTR_EN;
+ pci_write_config_word(dev, pos + PCI_EXP_DEVCTL2, ctrl);
+
+ return 0;
+}
+EXPORT_SYMBOL(pci_enable_ltr);
+
+/**
+ * pci_disable_ltr - disable latency tolerance reporting
+ * @dev: PCI device
+ */
+void pci_disable_ltr(struct pci_dev *dev)
+{
+ int pos;
+ u16 ctrl;
+
+ if (!pci_ltr_supported(dev))
+ return;
+
+ pos = pci_pcie_cap(dev);
+ if (!pos)
+ return;
+
+ /* Only primary function can enable/disable LTR */
+ if (PCI_FUNC(dev->devfn) != 0)
+ return;
+
+ pci_read_config_word(dev, pos + PCI_EXP_DEVCTL2, &ctrl);
+ ctrl &= ~PCI_EXP_LTR_EN;
+ pci_write_config_word(dev, pos + PCI_EXP_DEVCTL2, ctrl);
+}
+EXPORT_SYMBOL(pci_disable_ltr);
+
+static int __pci_ltr_scale(int *val)
+{
+ int scale = 0;
+
+ while (*val > 1023) {
+ *val = (*val + 31) / 32;
+ scale++;
+ }
+ return scale;
+}
+
+/**
+ * pci_set_ltr - set LTR latency values
+ * @dev: PCI device
+ * @snoop_lat_ns: snoop latency in nanoseconds
+ * @nosnoop_lat_ns: nosnoop latency in nanoseconds
+ *
+ * Figure out the scale and set the LTR values accordingly.
+ */
+int pci_set_ltr(struct pci_dev *dev, int snoop_lat_ns, int nosnoop_lat_ns)
+{
+ int pos, ret, snoop_scale, nosnoop_scale;
+ u16 val;
+
+ if (!pci_ltr_supported(dev))
+ return -ENOTSUPP;
+
+ snoop_scale = __pci_ltr_scale(&snoop_lat_ns);
+ nosnoop_scale = __pci_ltr_scale(&nosnoop_lat_ns);
+
+ if (snoop_lat_ns > PCI_LTR_VALUE_MASK ||
+ nosnoop_lat_ns > PCI_LTR_VALUE_MASK)
+ return -EINVAL;
+
+ if ((snoop_scale > (PCI_LTR_SCALE_MASK >> PCI_LTR_SCALE_SHIFT)) ||
+ (nosnoop_scale > (PCI_LTR_SCALE_MASK >> PCI_LTR_SCALE_SHIFT)))
+ return -EINVAL;
+
+ pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_LTR);
+ if (!pos)
+ return -ENOTSUPP;
+
+ val = (snoop_scale << PCI_LTR_SCALE_SHIFT) | snoop_lat_ns;
+ ret = pci_write_config_word(dev, pos + PCI_LTR_MAX_SNOOP_LAT, val);
+ if (ret != 4)
+ return -EIO;
+
+ val = (nosnoop_scale << PCI_LTR_SCALE_SHIFT) | nosnoop_lat_ns;
+ ret = pci_write_config_word(dev, pos + PCI_LTR_MAX_NOSNOOP_LAT, val);
+ if (ret != 4)
+ return -EIO;
+
+ return 0;
+}
+EXPORT_SYMBOL(pci_set_ltr);
+
static int pci_acs_enable;
/**
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 45a035c..df4d69b 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -840,6 +840,11 @@ enum pci_obff_signal_type {
int pci_enable_obff(struct pci_dev *dev, enum pci_obff_signal_type);
void pci_disable_obff(struct pci_dev *dev);
+bool pci_ltr_supported(struct pci_dev *dev);
+int pci_enable_ltr(struct pci_dev *dev);
+void pci_disable_ltr(struct pci_dev *dev);
+int pci_set_ltr(struct pci_dev *dev, int snoop_lat_ns, int nosnoop_lat_ns);
+
/* For use by arch with custom probe code */
void set_pcie_port_type(struct pci_dev *pdev);
void set_pcie_hotplug_bridge(struct pci_dev *pdev);
diff --git a/include/linux/pci_regs.h b/include/linux/pci_regs.h
index aa42026..e884096 100644
--- a/include/linux/pci_regs.h
+++ b/include/linux/pci_regs.h
@@ -508,6 +508,7 @@
#define PCI_EXP_RTSTA_PENDING 0x20000 /* PME pending */
#define PCI_EXP_DEVCAP2 36 /* Device Capabilities 2 */
#define PCI_EXP_DEVCAP2_ARI 0x20 /* Alternative Routing-ID */
+#define PCI_EXP_DEVCAP2_LTR 0x800 /* Latency tolerance reporting */
#define PCI_EXP_OBFF_MASK 0xc0000 /* OBFF support mechanism */
#define PCI_EXP_OBFF_MSG 0x40000 /* New message signaling */
#define PCI_EXP_OBFF_WAKE 0x80000 /* Re-use WAKE# for OBFF */
@@ -515,6 +516,7 @@
#define PCI_EXP_DEVCTL2_ARI 0x20 /* Alternative Routing-ID */
#define PCI_EXP_IDO_REQ_EN 0x100 /* ID-based ordering request enable */
#define PCI_EXP_IDO_CMP_EN 0x200 /* ID-based ordering completion enable */
+#define PCI_EXP_LTR_EN 0x400 /* Latency tolerance reporting */
#define PCI_EXP_OBFF_MSGA_EN 0x2000 /* OBFF enable with Message type A */
#define PCI_EXP_OBFF_MSGB_EN 0x4000 /* OBFF enable with Message type B */
#define PCI_EXP_OBFF_WAKE_EN 0x6000 /* OBFF using WAKE# signaling */
@@ -535,6 +537,7 @@
#define PCI_EXT_CAP_ID_ARI 14
#define PCI_EXT_CAP_ID_ATS 15
#define PCI_EXT_CAP_ID_SRIOV 16
+#define PCI_EXT_CAP_ID_LTR 24
/* Advanced Error Reporting */
#define PCI_ERR_UNCOR_STATUS 4 /* Uncorrectable Error Status */
@@ -691,6 +694,12 @@
#define PCI_SRIOV_VFM_MO 0x2 /* Active.MigrateOut */
#define PCI_SRIOV_VFM_AV 0x3 /* Active.Available */
+#define PCI_LTR_MAX_SNOOP_LAT 0x4
+#define PCI_LTR_MAX_NOSNOOP_LAT 0x6
+#define PCI_LTR_VALUE_MASK 0x000003ff
+#define PCI_LTR_SCALE_MASK 0x00001c00
+#define PCI_LTR_SCALE_SHIFT 10
+
/* Access Control Service */
#define PCI_ACS_CAP 0x04 /* ACS Capability Register */
#define PCI_ACS_SV 0x01 /* Source Validation */
--
1.7.1
--
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