i2c-nforce2: Add support for multiplexing on the Tyan S4985

Just like the Tyan S4882, the S4985 uses a multiplexer to give access
to all 16 memory module SPD EEPROMs. This specific i2c-nforce2-s4985
driver adds support for this. It is heavily based on the older
i2c-amd756-s4882 driver.

As more mainboards will use multiplexer chips, we will have to find a
way to support them without having to write a new specfic driver for
each. The recent changes to the i2c subsystem should help us, and the
new gpio subsystem might help, too.

Signed-off-by: Jean Delvare <khali@linux-fr.org>

4 files changed, 287 insertions, 0 deletions

diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig
index 48438cc5d0ca..00d76e13588f 100644
--- a/drivers/i2c/busses/Kconfig
+++ b/drivers/i2c/busses/Kconfig
@@ -315,6 +315,19 @@ config I2C_NFORCE2
           This driver can also be built as a module.  If so, the module
           will be called i2c-nforce2.
 
+config I2C_NFORCE2_S4985
+        tristate "SMBus multiplexing on the Tyan S4985"
+        depends on I2C_NFORCE2 && EXPERIMENTAL
+        help
+          Enabling this option will add specific SMBus support for the Tyan
+          S4985 motherboard.  On this 4-CPU board, the SMBus is multiplexed
+          over 4 different channels, where the various memory module EEPROMs
+          live.  Saying yes here will give you access to these in addition
+          to the trunk.
+
+          This driver can also be built as a module.  If so, the module
+          will be called i2c-nforce2-s4985.
+
 config I2C_OCORES
         tristate "OpenCores I2C Controller"
         depends on EXPERIMENTAL
diff --git a/drivers/i2c/busses/Makefile b/drivers/i2c/busses/Makefile
index e8c882a5ea66..8b0a8c257905 100644
--- a/drivers/i2c/busses/Makefile
+++ b/drivers/i2c/busses/Makefile
@@ -24,6 +24,7 @@ obj-$(CONFIG_I2C_POWERMAC)	+= i2c-powermac.o
 obj-$(CONFIG_I2C_MPC)           += i2c-mpc.o
 obj-$(CONFIG_I2C_MV64XXX)       += i2c-mv64xxx.o
 obj-$(CONFIG_I2C_NFORCE2)       += i2c-nforce2.o
+obj-$(CONFIG_I2C_NFORCE2_S4985) += i2c-nforce2-s4985.o
 obj-$(CONFIG_I2C_OCORES)        += i2c-ocores.o
 obj-$(CONFIG_I2C_OMAP)          += i2c-omap.o
 obj-$(CONFIG_I2C_PARPORT)       += i2c-parport.o
diff --git a/drivers/i2c/busses/i2c-nforce2-s4985.c b/drivers/i2c/busses/i2c-nforce2-s4985.c
new file mode 100644
index 000000000000..6a8995dfd0bb
--- /dev/null
+++ b/drivers/i2c/busses/i2c-nforce2-s4985.c
@@ -0,0 +1,257 @@
+/*
+ * i2c-nforce2-s4985.c - i2c-nforce2 extras for the Tyan S4985 motherboard
+ *
+ * Copyright (C) 2008 Jean Delvare <khali@linux-fr.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+/*
+ * We select the channels by sending commands to the Philips
+ * PCA9556 chip at I2C address 0x18. The main adapter is used for
+ * the non-multiplexed part of the bus, and 4 virtual adapters
+ * are defined for the multiplexed addresses: 0x50-0x53 (memory
+ * module EEPROM) located on channels 1-4. We define one virtual
+ * adapter per CPU, which corresponds to one multiplexed channel:
+ *   CPU0: virtual adapter 1, channel 1
+ *   CPU1: virtual adapter 2, channel 2
+ *   CPU2: virtual adapter 3, channel 3
+ *   CPU3: virtual adapter 4, channel 4
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/init.h>
+#include <linux/i2c.h>
+#include <linux/mutex.h>
+
+extern struct i2c_adapter *nforce2_smbus;
+
+static struct i2c_adapter *s4985_adapter;
+static struct i2c_algorithm *s4985_algo;
+
+/* Wrapper access functions for multiplexed SMBus */
+static DEFINE_MUTEX(nforce2_lock);
+
+static s32 nforce2_access_virt0(struct i2c_adapter *adap, u16 addr,
+                                unsigned short flags, char read_write,
+                                u8 command, int size,
+                                union i2c_smbus_data *data)
+{
+        int error;
+
+        /* We exclude the multiplexed addresses */
+        if ((addr & 0xfc) == 0x50 || (addr & 0xfc) == 0x30
+         || addr == 0x18)
+                return -ENXIO;
+
+        mutex_lock(&nforce2_lock);
+        error = nforce2_smbus->algo->smbus_xfer(adap, addr, flags, read_write,
+                                                command, size, data);
+        mutex_unlock(&nforce2_lock);
+
+        return error;
+}
+
+/* We remember the last used channels combination so as to only switch
+   channels when it is really needed. This greatly reduces the SMBus
+   overhead, but also assumes that nobody will be writing to the PCA9556
+   in our back. */
+static u8 last_channels;
+
+static inline s32 nforce2_access_channel(struct i2c_adapter *adap, u16 addr,
+                                         unsigned short flags, char read_write,
+                                         u8 command, int size,
+                                         union i2c_smbus_data *data,
+                                         u8 channels)
+{
+        int error;
+
+        /* We exclude the non-multiplexed addresses */
+        if ((addr & 0xfc) != 0x50 && (addr & 0xfc) != 0x30)
+                return -ENXIO;
+
+        mutex_lock(&nforce2_lock);
+        if (last_channels != channels) {
+                union i2c_smbus_data mplxdata;
+                mplxdata.byte = channels;
+
+                error = nforce2_smbus->algo->smbus_xfer(adap, 0x18, 0,
+                                                        I2C_SMBUS_WRITE, 0x01,
+                                                        I2C_SMBUS_BYTE_DATA,
+                                                        &mplxdata);
+                if (error)
+                        goto UNLOCK;
+                last_channels = channels;
+        }
+        error = nforce2_smbus->algo->smbus_xfer(adap, addr, flags, read_write,
+                                                command, size, data);
+
+UNLOCK:
+        mutex_unlock(&nforce2_lock);
+        return error;
+}
+
+static s32 nforce2_access_virt1(struct i2c_adapter *adap, u16 addr,
+                                unsigned short flags, char read_write,
+                                u8 command, int size,
+                                union i2c_smbus_data *data)
+{
+        /* CPU0: channel 1 enabled */
+        return nforce2_access_channel(adap, addr, flags, read_write, command,
+                                      size, data, 0x02);
+}
+
+static s32 nforce2_access_virt2(struct i2c_adapter *adap, u16 addr,
+                                unsigned short flags, char read_write,
+                                u8 command, int size,
+                                union i2c_smbus_data *data)
+{
+        /* CPU1: channel 2 enabled */
+        return nforce2_access_channel(adap, addr, flags, read_write, command,
+                                      size, data, 0x04);
+}
+
+static s32 nforce2_access_virt3(struct i2c_adapter *adap, u16 addr,
+                                unsigned short flags, char read_write,
+                                u8 command, int size,
+                                union i2c_smbus_data *data)
+{
+        /* CPU2: channel 3 enabled */
+        return nforce2_access_channel(adap, addr, flags, read_write, command,
+                                      size, data, 0x08);
+}
+
+static s32 nforce2_access_virt4(struct i2c_adapter *adap, u16 addr,
+                                unsigned short flags, char read_write,
+                                u8 command, int size,
+                                union i2c_smbus_data *data)
+{
+        /* CPU3: channel 4 enabled */
+        return nforce2_access_channel(adap, addr, flags, read_write, command,
+                                      size, data, 0x10);
+}
+
+static int __init nforce2_s4985_init(void)
+{
+        int i, error;
+        union i2c_smbus_data ioconfig;
+
+        /* Unregister physical bus */
+        if (!nforce2_smbus)
+                return -ENODEV;
+        error = i2c_del_adapter(nforce2_smbus);
+        if (error) {
+                dev_err(&nforce2_smbus->dev, "Physical bus removal failed\n");
+                goto ERROR0;
+        }
+
+        printk(KERN_INFO "Enabling SMBus multiplexing for Tyan S4985\n");
+        /* Define the 5 virtual adapters and algorithms structures */
+        s4985_adapter = kzalloc(5 * sizeof(struct i2c_adapter), GFP_KERNEL);
+        if (!s4985_adapter) {
+                error = -ENOMEM;
+                goto ERROR1;
+        }
+        s4985_algo = kzalloc(5 * sizeof(struct i2c_algorithm), GFP_KERNEL);
+        if (!s4985_algo) {
+                error = -ENOMEM;
+                goto ERROR2;
+        }
+
+        /* Fill in the new structures */
+        s4985_algo[0] = *(nforce2_smbus->algo);
+        s4985_algo[0].smbus_xfer = nforce2_access_virt0;
+        s4985_adapter[0] = *nforce2_smbus;
+        s4985_adapter[0].algo = s4985_algo;
+        s4985_adapter[0].dev.parent = nforce2_smbus->dev.parent;
+        for (i = 1; i < 5; i++) {
+                s4985_algo[i] = *(nforce2_smbus->algo);
+                s4985_adapter[i] = *nforce2_smbus;
+                snprintf(s4985_adapter[i].name, sizeof(s4985_adapter[i].name),
+                         "SMBus nForce2 adapter (CPU%d)", i - 1);
+                s4985_adapter[i].algo = s4985_algo + i;
+                s4985_adapter[i].dev.parent = nforce2_smbus->dev.parent;
+        }
+        s4985_algo[1].smbus_xfer = nforce2_access_virt1;
+        s4985_algo[2].smbus_xfer = nforce2_access_virt2;
+        s4985_algo[3].smbus_xfer = nforce2_access_virt3;
+        s4985_algo[4].smbus_xfer = nforce2_access_virt4;
+
+        /* Configure the PCA9556 multiplexer */
+        ioconfig.byte = 0x00; /* All I/O to output mode */
+        error = nforce2_smbus->algo->smbus_xfer(nforce2_smbus, 0x18, 0,
+                                                I2C_SMBUS_WRITE, 0x03,
+                                                I2C_SMBUS_BYTE_DATA, &ioconfig);
+        if (error) {
+                dev_err(&nforce2_smbus->dev, "PCA9556 configuration failed\n");
+                error = -EIO;
+                goto ERROR3;
+        }
+
+        /* Register virtual adapters */
+        for (i = 0; i < 5; i++) {
+                error = i2c_add_adapter(s4985_adapter + i);
+                if (error) {
+                        dev_err(&nforce2_smbus->dev,
+                                "Virtual adapter %d registration "
+                                "failed, module not inserted\n", i);
+                        for (i--; i >= 0; i--)
+                                i2c_del_adapter(s4985_adapter + i);
+                        goto ERROR3;
+                }
+        }
+
+        return 0;
+
+ERROR3:
+        kfree(s4985_algo);
+        s4985_algo = NULL;
+ERROR2:
+        kfree(s4985_adapter);
+        s4985_adapter = NULL;
+ERROR1:
+        /* Restore physical bus */
+        i2c_add_adapter(nforce2_smbus);
+ERROR0:
+        return error;
+}
+
+static void __exit nforce2_s4985_exit(void)
+{
+        if (s4985_adapter) {
+                int i;
+
+                for (i = 0; i < 5; i++)
+                        i2c_del_adapter(s4985_adapter+i);
+                kfree(s4985_adapter);
+                s4985_adapter = NULL;
+        }
+        kfree(s4985_algo);
+        s4985_algo = NULL;
+
+        /* Restore physical bus */
+        if (i2c_add_adapter(nforce2_smbus))
+                dev_err(&nforce2_smbus->dev, "Physical bus restoration "
+                        "failed\n");
+}
+
+MODULE_AUTHOR("Jean Delvare <khali@linux-fr.org>");
+MODULE_DESCRIPTION("S4985 SMBus multiplexing");
+MODULE_LICENSE("GPL");
+
+module_init(nforce2_s4985_init);
+module_exit(nforce2_s4985_exit);
diff --git a/drivers/i2c/busses/i2c-nforce2.c b/drivers/i2c/busses/i2c-nforce2.c
index 43c9f8df9509..f95efff9b3d1 100644
--- a/drivers/i2c/busses/i2c-nforce2.c
+++ b/drivers/i2c/busses/i2c-nforce2.c
@@ -124,6 +124,20 @@ static struct dmi_system_id __devinitdata nforce2_dmi_blacklist2[] = {
 
 static struct pci_driver nforce2_driver;
 
+/* For multiplexing support, we need a global reference to the 1st
+   SMBus channel */
+#if defined CONFIG_I2C_NFORCE2_S4985 || defined CONFIG_I2C_NFORCE2_S4985_MODULE
+struct i2c_adapter *nforce2_smbus;
+EXPORT_SYMBOL_GPL(nforce2_smbus);
+
+static void nforce2_set_reference(struct i2c_adapter *adap)
+{
+        nforce2_smbus = adap;
+}
+#else
+static inline void nforce2_set_reference(struct i2c_adapter *adap) { }
+#endif
+
 static void nforce2_abort(struct i2c_adapter *adap)
 {
         struct nforce2_smbus *smbus = adap->algo_data;
@@ -398,6 +412,7 @@ static int __devinit nforce2_probe(struct pci_dev *dev, const struct pci_device_
                 return -ENODEV;
         }
 
+        nforce2_set_reference(&smbuses[0].adapter);
         return 0;
 }
 
@@ -406,6 +421,7 @@ static void __devexit nforce2_remove(struct pci_dev *dev)
 {
         struct nforce2_smbus *smbuses = (void*) pci_get_drvdata(dev);
 
+        nforce2_set_reference(NULL);
         if (smbuses[0].base) {
                 i2c_del_adapter(&smbuses[0].adapter);
                 release_region(smbuses[0].base, smbuses[0].size);