Generic bitbanged MDIO library

Previously, bitbanged MDIO was only supported in individual
hardware-specific drivers.  This code factors out the higher level
protocol implementation, reducing the hardware-specific portion to
functions setting direction, data, and clock.

Signed-off-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

3 files changed, 197 insertions, 0 deletions

diff --git a/drivers/net/phy/Kconfig b/drivers/net/phy/Kconfig
index 432c210513b..54b2ba99664 100644
--- a/drivers/net/phy/Kconfig
+++ b/drivers/net/phy/Kconfig
@@ -90,4 +90,13 @@ config FIXED_MII_AMNT
         This control will have specified number allocated for each fixed
         PHY type enabled.
 
+config MDIO_BITBANG
+        tristate "Support for bitbanged MDIO buses"
+        help
+          This module implements the MDIO bus protocol in software,
+          for use by low level drivers that export the ability to
+          drive the relevant pins.
+
+          If in doubt, say N.
+
 endif # PHYLIB
diff --git a/drivers/net/phy/Makefile b/drivers/net/phy/Makefile
index 8885650647f..3d6cc7b67a8 100644
--- a/drivers/net/phy/Makefile
+++ b/drivers/net/phy/Makefile
@@ -13,3 +13,4 @@ obj-$(CONFIG_VITESSE_PHY)	+= vitesse.o
 obj-$(CONFIG_BROADCOM_PHY)      += broadcom.o
 obj-$(CONFIG_ICPLUS_PHY)        += icplus.o
 obj-$(CONFIG_FIXED_PHY)         += fixed.o
+obj-$(CONFIG_MDIO_BITBANG)      += mdio-bitbang.o
diff --git a/drivers/net/phy/mdio-bitbang.c b/drivers/net/phy/mdio-bitbang.c
new file mode 100644
index 00000000000..8cd243d92af
--- /dev/null
+++ b/drivers/net/phy/mdio-bitbang.c
@@ -0,0 +1,187 @@
+/*
+ * Bitbanged MDIO support.
+ *
+ * Author: Scott Wood <scottwood@freescale.com>
+ * Copyright (c) 2007 Freescale Semiconductor
+ *
+ * Based on CPM2 MDIO code which is:
+ *
+ * Copyright (c) 2003 Intracom S.A.
+ *  by Pantelis Antoniou <panto@intracom.gr>
+ *
+ * 2005 (c) MontaVista Software, Inc.
+ * Vitaly Bordug <vbordug@ru.mvista.com>
+ *
+ * This file is licensed under the terms of the GNU General Public License
+ * version 2. This program is licensed "as is" without any warranty of any
+ * kind, whether express or implied.
+ */
+
+#include <linux/module.h>
+#include <linux/mdio-bitbang.h>
+#include <linux/slab.h>
+#include <linux/types.h>
+#include <linux/delay.h>
+
+#define MDIO_READ 1
+#define MDIO_WRITE 0
+
+#define MDIO_SETUP_TIME 10
+#define MDIO_HOLD_TIME 10
+
+/* Minimum MDC period is 400 ns, plus some margin for error.  MDIO_DELAY
+ * is done twice per period.
+ */
+#define MDIO_DELAY 250
+
+/* The PHY may take up to 300 ns to produce data, plus some margin
+ * for error.
+ */
+#define MDIO_READ_DELAY 350
+
+/* MDIO must already be configured as output. */
+static void mdiobb_send_bit(struct mdiobb_ctrl *ctrl, int val)
+{
+        const struct mdiobb_ops *ops = ctrl->ops;
+
+        ops->set_mdio_data(ctrl, val);
+        ndelay(MDIO_DELAY);
+        ops->set_mdc(ctrl, 1);
+        ndelay(MDIO_DELAY);
+        ops->set_mdc(ctrl, 0);
+}
+
+/* MDIO must already be configured as input. */
+static int mdiobb_get_bit(struct mdiobb_ctrl *ctrl)
+{
+        const struct mdiobb_ops *ops = ctrl->ops;
+
+        ndelay(MDIO_DELAY);
+        ops->set_mdc(ctrl, 1);
+        ndelay(MDIO_READ_DELAY);
+        ops->set_mdc(ctrl, 0);
+
+        return ops->get_mdio_data(ctrl);
+}
+
+/* MDIO must already be configured as output. */
+static void mdiobb_send_num(struct mdiobb_ctrl *ctrl, u16 val, int bits)
+{
+        int i;
+
+        for (i = bits - 1; i >= 0; i--)
+                mdiobb_send_bit(ctrl, (val >> i) & 1);
+}
+
+/* MDIO must already be configured as input. */
+static u16 mdiobb_get_num(struct mdiobb_ctrl *ctrl, int bits)
+{
+        int i;
+        u16 ret = 0;
+
+        for (i = bits - 1; i >= 0; i--) {
+                ret <<= 1;
+                ret |= mdiobb_get_bit(ctrl);
+        }
+
+        return ret;
+}
+
+/* Utility to send the preamble, address, and
+ * register (common to read and write).
+ */
+static void mdiobb_cmd(struct mdiobb_ctrl *ctrl, int read, u8 phy, u8 reg)
+{
+        const struct mdiobb_ops *ops = ctrl->ops;
+        int i;
+
+        ops->set_mdio_dir(ctrl, 1);
+
+        /*
+         * Send a 32 bit preamble ('1's) with an extra '1' bit for good
+         * measure.  The IEEE spec says this is a PHY optional
+         * requirement.  The AMD 79C874 requires one after power up and
+         * one after a MII communications error.  This means that we are
+         * doing more preambles than we need, but it is safer and will be
+         * much more robust.
+         */
+
+        for (i = 0; i < 32; i++)
+                mdiobb_send_bit(ctrl, 1);
+
+        /* send the start bit (01) and the read opcode (10) or write (10) */
+        mdiobb_send_bit(ctrl, 0);
+        mdiobb_send_bit(ctrl, 1);
+        mdiobb_send_bit(ctrl, read);
+        mdiobb_send_bit(ctrl, !read);
+
+        mdiobb_send_num(ctrl, phy, 5);
+        mdiobb_send_num(ctrl, reg, 5);
+}
+
+
+static int mdiobb_read(struct mii_bus *bus, int phy, int reg)
+{
+        struct mdiobb_ctrl *ctrl = bus->priv;
+        int ret, i;
+
+        mdiobb_cmd(ctrl, MDIO_READ, phy, reg);
+        ctrl->ops->set_mdio_dir(ctrl, 0);
+
+        /* check the turnaround bit: the PHY should be driving it to zero */
+        if (mdiobb_get_bit(ctrl) != 0) {
+                /* PHY didn't drive TA low -- flush any bits it
+                 * may be trying to send.
+                 */
+                for (i = 0; i < 32; i++)
+                        mdiobb_get_bit(ctrl);
+
+                return 0xffff;
+        }
+
+        ret = mdiobb_get_num(ctrl, 16);
+        mdiobb_get_bit(ctrl);
+        return ret;
+}
+
+static int mdiobb_write(struct mii_bus *bus, int phy, int reg, u16 val)
+{
+        struct mdiobb_ctrl *ctrl = bus->priv;
+
+        mdiobb_cmd(ctrl, MDIO_WRITE, phy, reg);
+
+        /* send the turnaround (10) */
+        mdiobb_send_bit(ctrl, 1);
+        mdiobb_send_bit(ctrl, 0);
+
+        mdiobb_send_num(ctrl, val, 16);
+
+        ctrl->ops->set_mdio_dir(ctrl, 0);
+        mdiobb_get_bit(ctrl);
+        return 0;
+}
+
+struct mii_bus *alloc_mdio_bitbang(struct mdiobb_ctrl *ctrl)
+{
+        struct mii_bus *bus;
+
+        bus = kzalloc(sizeof(struct mii_bus), GFP_KERNEL);
+        if (!bus)
+                return NULL;
+
+        __module_get(ctrl->ops->owner);
+
+        bus->read = mdiobb_read;
+        bus->write = mdiobb_write;
+        bus->priv = ctrl;
+
+        return bus;
+}
+
+void free_mdio_bitbang(struct mii_bus *bus)
+{
+        struct mdiobb_ctrl *ctrl = bus->priv;
+
+        module_put(ctrl->ops->owner);
+        kfree(bus);
+}