Author: ian
Date: Thu Jun 29 01:50:58 2017
New Revision: 320461
URL: https://svnweb.freebsd.org/changeset/base/320461
Log:
Add iic_recover_bus(), a helper function that can be used by any i2c driver
which is able to manipulate the clock and data lines directly.
When an i2c bus is hung by a slave device stuck in the middle of a
transaction that didn't complete properly, this function manipulates the
clock and data lines in a sequence known to reliably reset slave devices.
The most common cause of a hung i2c bus is a system reboot in the middle of
an i2c transfer (so it doesnt' happen often, but now there is a way other
than power cycling to recover from it).
Added:
head/sys/dev/iicbus/iic_recover_bus.c (contents, props changed)
head/sys/dev/iicbus/iic_recover_bus.h (contents, props changed)
Added: head/sys/dev/iicbus/iic_recover_bus.c
==============================================================================
--- /dev/null 00:00:00 1970 (empty, because file is newly added)
+++ head/sys/dev/iicbus/iic_recover_bus.c Thu Jun 29 01:50:58 2017
(r320461)
@@ -0,0 +1,124 @@
+/*-
+ * Copyright (c) 2017 Ian Lepore <i...@freebsd.org>
+ * All rights reserved.
+ *
+ * Development sponsored by Microsemi, Inc.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+/*
+ * Helper code to recover a hung i2c bus by bit-banging a recovery sequence.
+ *
+ * An i2c bus can be hung by a slave driving the clock (rare) or data lines
low.
+ * The most common cause is a partially-completed transaction such as rebooting
+ * while a slave is sending a byte of data. Because i2c allows the clock to
+ * freeze for any amount of time, the slave device will continue driving the
+ * data line until power is removed, or the clock cycles enough times to
+ * complete the current byte. After completing any partial byte, a START/STOP
+ * sequence resets the slave and the bus is recovered.
+ *
+ * Any i2c driver which is able to manually set the level of the clock and data
+ * lines can use this common code for bus recovery. On many SOCs that have
+ * embedded i2c controllers, the i2c pins can be temporarily reassigned as gpio
+ * pins to do the bus recovery, then can be assigned back to the i2c hardware.
+ */
+
+#include "opt_platform.h"
+
+#include <sys/param.h>
+#include <sys/systm.h>
+#include <sys/bus.h>
+
+#include <dev/iicbus/iic_recover_bus.h>
+#include <dev/iicbus/iiconf.h>
+
+int
+iic_recover_bus(struct iicrb_pin_access *pins)
+{
+ const u_int timeout_us = 40000;
+ const u_int delay_us = 500;
+ int i;
+
+ /*
+ * Start with clock and data high.
+ */
+ pins->setsda(pins->ctx, 1);
+ pins->setscl(pins->ctx, 1);
+
+ /*
+ * At this point, SCL should be high. If it's not, some slave on the
+ * bus is doing clock-stretching and we should wait a while. If that
+ * slave is completely locked up there may be no way to recover at all.
+ * We wait up to 40 milliseconds, a seriously pessimistic time (even a
+ * cheap eeprom has a max post-write delay of only 10ms), and also long
+ * enough to allow SMB slaves to timeout normally after 35ms.
+ */
+ for (i = 0; i < timeout_us; i += delay_us) {
+ if (pins->getscl(pins->ctx))
+ break;
+ DELAY(delay_us);
+ }
+ if (i >= timeout_us)
+ return (IIC_EBUSERR);
+
+ /*
+ * At this point we should be able to control the clock line. Some
+ * slave may be part way through a byte transfer, and could be holding
+ * the data line low waiting for more clock pulses to finish the byte.
+ * Cycle the clock until we see the data line go high, but only up to 9
+ * times because if it's not free after 9 clocks we're never going to
+ * win this battle. We do 9 max because that's a byte plus an ack/nack
+ * bit, after which the slave must not be driving the data line anymore.
+ */
+ for (i = 0; ; ++i) {
+ if (pins->getsda(pins->ctx))
+ break;
+ if (i == 9)
+ return (IIC_EBUSERR);
+ pins->setscl(pins->ctx, 0);
+ DELAY(5);
+ pins->setscl(pins->ctx, 1);
+ DELAY(5);
+ }
+
+ /*
+ * At this point we should be in control of both the clock and data
+ * lines, and both lines should be high. To complete the reset of a
+ * slave that was part way through a transaction, we need to do a
+ * START/STOP sequence, which leaves both lines high at the end.
+ * - START: SDA transitions high->low while SCL remains high.
+ * - STOP: SDA transitions low->high while SCL remains high.
+ * Note that even though the clock line remains high, we transition the
+ * data line no faster than it would change state with a 100khz clock.
+ */
+ pins->setsda(pins->ctx, 0);
+ DELAY(5);
+ pins->setsda(pins->ctx, 1);
+ DELAY(5);
+
+ return (0);
+}
+
Added: head/sys/dev/iicbus/iic_recover_bus.h
==============================================================================
--- /dev/null 00:00:00 1970 (empty, because file is newly added)
+++ head/sys/dev/iicbus/iic_recover_bus.h Thu Jun 29 01:50:58 2017
(r320461)
@@ -0,0 +1,57 @@
+/*-
+ * Copyright (c) 2017 Ian Lepore <i...@freebsd.org>
+ * All rights reserved.
+ *
+ * Development sponsored by Microsemi, Inc.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * $FreeBSD$
+ */
+
+/*
+ * Helper code to recover a hung i2c bus by bit-banging a recovery sequence.
+ */
+
+#ifndef _IICBUS_IIC_RECOVER_BUS_H_
+#define _IICBUS_IIC_RECOVER_BUS_H_
+
+struct iicrb_pin_access {
+ void *ctx;
+ int (*getsda)(void *ctx);
+ void (*setsda)(void *ctx, int value);
+ int (*getscl)(void *ctx);
+ void (*setscl)(void *ctx, int value);
+};
+
+/*
+ * Drive the bus-recovery logic by manipulating the line states using the
+ * caller-provided functions. This does not block or sleep or acquire any
locks
+ * (unless the provided pin access functions do so). It uses DELAY() to pace
+ * bits on the bus.
+ *
+ * Returns 0 if the bus is functioning properly or IIC_EBUSERR if the recovery
+ * attempt failed and some slave device is still driving the bus.
+ */
+int iic_recover_bus(struct iicrb_pin_access *pins);
+
+#endif
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