PCI: add PCI-X/PCI-Express read control interfaces

This patch introduces an interface to read and write PCI-X / PCI-Express
maximum read byte count values from PCI config space. There is a second
function that returns the maximum _designed_ read byte count, which marks the
maximum value for a device, since some drivers try to set MMRBC to the
highest allowed value and rely on such a function.

Based on patch set by Stephen Hemminger <[e-mail]>

Cc: Stephen Hemminger <[e-mail]>
Signed-off-by: Peter Oruba <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/pci/pci.c

···
 #endif
 
 /**
+ * pcix_get_max_mmrbc - get PCI-X maximum designed memory read byte count
+ * @dev: PCI device to query
+ *
+ * Returns mmrbc: maximum designed memory read count in bytes
+ *    or appropriate error value.
+ */
+int pcix_get_max_mmrbc(struct pci_dev *dev)
+{
+	int ret, err, cap;
+	u32 stat;
+
+	cap = pci_find_capability(dev, PCI_CAP_ID_PCIX);
+	if (!cap)
+		return -EINVAL;
+
+	err = pci_read_config_dword(dev, cap + PCI_X_STATUS, &stat);
+	if (err)
+		return -EINVAL;
+
+	ret = (stat & PCI_X_STATUS_MAX_READ) >> 12;
+
+	return ret;
+}
+EXPORT_SYMBOL(pcix_get_max_mmrbc);
+
+/**
+ * pcix_get_mmrbc - get PCI-X maximum memory read byte count
+ * @dev: PCI device to query
+ *
+ * Returns mmrbc: maximum memory read count in bytes
+ *    or appropriate error value.
+ */
+int pcix_get_mmrbc(struct pci_dev *dev)
+{
+	int ret, cap;
+	u32 cmd;
+
+	cap = pci_find_capability(dev, PCI_CAP_ID_PCIX);
+	if (!cap)
+		return -EINVAL;
+
+	ret = pci_read_config_dword(dev, cap + PCI_X_CMD, &cmd);
+	if (!ret)
+		ret = 512 << ((cmd & PCI_X_CMD_MAX_READ) >> 2);
+
+	return ret;
+}
+EXPORT_SYMBOL(pcix_get_mmrbc);
+
+/**
+ * pcix_set_mmrbc - set PCI-X maximum memory read byte count
+ * @dev: PCI device to query
+ * @mmrbc: maximum memory read count in bytes
+ *    valid values are 512, 1024, 2048, 4096
+ *
+ * If possible sets maximum memory read byte count, some bridges have erratas
+ * that prevent this.
+ */
+int pcix_set_mmrbc(struct pci_dev *dev, int mmrbc)
+{
+	int cap, err = -EINVAL;
+	u32 stat, cmd, v, o;
+
+	if (mmrbc < 512 || mmrbc > 4096 || (mmrbc & (mmrbc-1)))
+		goto out;
+
+	v = ffs(mmrbc) - 10;
+
+	cap = pci_find_capability(dev, PCI_CAP_ID_PCIX);
+	if (!cap)
+		goto out;
+
+	err = pci_read_config_dword(dev, cap + PCI_X_STATUS, &stat);
+	if (err)
+		goto out;
+
+	if (v > (stat & PCI_X_STATUS_MAX_READ) >> 21)
+		return -E2BIG;
+
+	err = pci_read_config_dword(dev, cap + PCI_X_CMD, &cmd);
+	if (err)
+		goto out;
+
+	o = (cmd & PCI_X_CMD_MAX_READ) >> 2;
+	if (o != v) {
+		if (v > o && dev->bus &&
+		   (dev->bus->bus_flags & PCI_BUS_FLAGS_NO_MMRBC))
+			return -EIO;
+
+		cmd &= ~PCI_X_CMD_MAX_READ;
+		cmd |= v << 2;
+		err = pci_write_config_dword(dev, cap + PCI_X_CMD, cmd);
+	}
+out:
+	return err;
+}
+EXPORT_SYMBOL(pcix_set_mmrbc);
+
+/**
+ * pcie_get_readrq - get PCI Express read request size
+ * @dev: PCI device to query
+ *
+ * Returns maximum memory read request in bytes
+ *    or appropriate error value.
+ */
+int pcie_get_readrq(struct pci_dev *dev)
+{
+	int ret, cap;
+	u16 ctl;
+
+	cap = pci_find_capability(dev, PCI_CAP_ID_EXP);
+	if (!cap)
+		return -EINVAL;
+
+	ret = pci_read_config_word(dev, cap + PCI_EXP_DEVCTL, &ctl);
+	if (!ret)
+	ret = 128 << ((ctl & PCI_EXP_DEVCTL_READRQ) >> 12);
+
+	return ret;
+}
+EXPORT_SYMBOL(pcie_get_readrq);
+
+/**
+ * pcie_set_readrq - set PCI Express maximum memory read request
+ * @dev: PCI device to query
+ * @count: maximum memory read count in bytes
+ *    valid values are 128, 256, 512, 1024, 2048, 4096
+ *
+ * If possible sets maximum read byte count
+ */
+int pcie_set_readrq(struct pci_dev *dev, int rq)
+{
+	int cap, err = -EINVAL;
+	u16 ctl, v;
+
+	if (rq < 128 || rq > 4096 || (rq & (rq-1)))
+		goto out;
+
+	v = (ffs(rq) - 8) << 12;
+
+	cap = pci_find_capability(dev, PCI_CAP_ID_EXP);
+	if (!cap)
+		goto out;
+
+	err = pci_read_config_word(dev, cap + PCI_EXP_DEVCTL, &ctl);
+	if (err)
+		goto out;
+
+	if ((ctl & PCI_EXP_DEVCTL_READRQ) != v) {
+		ctl &= ~PCI_EXP_DEVCTL_READRQ;
+		ctl |= v;
+		err = pci_write_config_dword(dev, cap + PCI_EXP_DEVCTL, ctl);
+	}
+
+out:
+	return err;
+}
+EXPORT_SYMBOL(pcie_set_readrq);
+
+/**
  * pci_select_bars - Make BAR mask from the type of resource
  * @dev: the PCI device for which BAR mask is made
  * @flags: resource type mask to be selected

drivers/pci/quirks.c

···
 DECLARE_PCI_FIXUP_RESUME(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_8131_BRIDGE, quirk_amd_8131_ioapic);
 #endif /* CONFIG_X86_IO_APIC */
 
+/*
+ * Some settings of MMRBC can lead to data corruption so block changes.
+ * See AMD 8131 HyperTransport PCI-X Tunnel Revision Guide
+ */
+static void __init quirk_amd_8131_mmrbc(struct pci_dev *dev)
+{
+	unsigned char revid;
+
+	pci_read_config_byte(dev, PCI_REVISION_ID, &revid);
+	if (dev->subordinate && revid <= 0x12) {
+		printk(KERN_INFO "AMD8131 rev %x detected, disabling PCI-X MMRBC\n",
+			revid);
+		dev->subordinate->bus_flags |= PCI_BUS_FLAGS_NO_MMRBC;
+	}
+}
+DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_8131_BRIDGE, quirk_amd_8131_mmrbc);
 
 /*
  * FIXME: it is questionable that quirk_via_acpi

include/linux/pci.h

···
 
 typedef unsigned short __bitwise pci_bus_flags_t;
 enum pci_bus_flags {
-	PCI_BUS_FLAGS_NO_MSI = (__force pci_bus_flags_t) 1,
+	PCI_BUS_FLAGS_NO_MSI   = (__force pci_bus_flags_t) 1,
+	PCI_BUS_FLAGS_NO_MMRBC = (__force pci_bus_flags_t) 2,
 };
 
 struct pci_cap_saved_state {
···
 void pci_msi_off(struct pci_dev *dev);
 int pci_set_dma_mask(struct pci_dev *dev, u64 mask);
 int pci_set_consistent_dma_mask(struct pci_dev *dev, u64 mask);
+int pcix_get_max_mmrbc(struct pci_dev *dev);
+int pcix_get_mmrbc(struct pci_dev *dev);
+int pcix_set_mmrbc(struct pci_dev *dev, int mmrbc);
+int pcie_set_readrq(struct pci_dev *dev, int rq);
 void pci_update_resource(struct pci_dev *dev, struct resource *res, int resno);
 int __must_check pci_assign_resource(struct pci_dev *dev, int i);
 int __must_check pci_assign_resource_fixed(struct pci_dev *dev, int i);