Commit 14911c6f authored by Wolfram Sang's avatar Wolfram Sang Committed by Wolfram Sang
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i2c: gpio: add fault injector

Add fault injection capabilities to the i2c-gpio driver. When connected
to another I2C bus, it can create unusual states which the other I2C bus
master driver needs to handle. Only for debugging!

Signed-off-by: default avatarWolfram Sang <>
parent 4d67c2e7
Linux I2C fault injection
The GPIO based I2C bus master driver can be configured to provide fault
injection capabilities. It is then meant to be connected to another I2C bus
which is driven by the I2C bus master driver under test. The GPIO fault
injection driver can create special states on the bus which the other I2C bus
master driver should handle gracefully.
Once the Kconfig option I2C_GPIO_FAULT_INJECTOR is enabled, there will be an
'i2c-fault-injector' subdirectory in the Kernel debugfs filesystem, usually
mounted at /sys/kernel/debug. There will be a separate subdirectory per GPIO
driven I2C bus. Each subdirectory will contain files to trigger the fault
injection. They will be described now along with their intended use-cases.
By reading this file, you get the current state of SCL. By writing, you can
change its state to either force it low or to release it again. So, by using
"echo 0 > scl" you force SCL low and thus, no communication will be possible
because the bus master under test will not be able to clock. It should detect
the condition of SCL being unresponsive and report an error to the upper
By reading this file, you get the current state of SDA. By writing, you can
change its state to either force it low or to release it again. So, by using
"echo 0 > sda" you force SDA low and thus, data cannot be transmitted. The bus
master under test should detect this condition and trigger a bus recovery (see
I2C specification version 4, section 3.1.16) using the helpers of the Linux I2C
core (see 'struct bus_recovery_info'). However, the bus recovery will not
succeed because SDA is still pinned low until you manually release it again
with "echo 1 > sda". A test with an automatic release can be done with the
'incomplete_transfer' file.
This file is write only and you need to write the address of an existing I2C
client device to it. Then, a transfer to this device will be started, but it
will stop at the ACK phase after the address of the client has been
transmitted. Because the device will ACK its presence, this results in SDA
being pulled low by the device while SCL is high. So, similar to the "sda" file
above, the bus master under test should detect this condition and try a bus
recovery. This time, however, it should succeed and the device should release
SDA after toggling SCL. Please note: there are I2C client devices which detect
a stuck SDA on their side and release it on their own after a few milliseconds.
Also, there are external devices deglitching and monitoring the I2C bus. They
can also detect a stuck SDA and will init a bus recovery on their own. If you
want to implement bus recovery in a bus master driver, make sure you checked
your hardware setup carefully before.
......@@ -603,6 +603,14 @@ config I2C_GPIO
This is a very simple bitbanging I2C driver utilizing the
arch-neutral GPIO API to control the SCL and SDA lines.
bool "GPIO-based fault injector"
depends on I2C_GPIO
This adds some functionality to the i2c-gpio driver which can inject
faults to an I2C bus, so another bus master can be stress-tested.
This is for debugging. If unsure, say 'no'.
tristate "Highlander FPGA SMBus interface"
depends on SH_HIGHLANDER
......@@ -7,6 +7,8 @@
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
#include <linux/debugfs.h>
#include <linux/delay.h>
#include <linux/i2c.h>
#include <linux/i2c-algo-bit.h>
#include <linux/i2c-gpio.h>
......@@ -23,6 +25,9 @@ struct i2c_gpio_private_data {
struct i2c_adapter adap;
struct i2c_algo_bit_data bit_data;
struct i2c_gpio_platform_data pdata;
struct dentry *debug_dir;
......@@ -64,6 +69,108 @@ static int i2c_gpio_getscl(void *data)
return gpiod_get_value(priv->scl);
static struct dentry *i2c_gpio_debug_dir;
#define setsda(bd, val) ((bd)->setsda((bd)->data, val))
#define setscl(bd, val) ((bd)->setscl((bd)->data, val))
#define getsda(bd) ((bd)->getsda((bd)->data))
#define getscl(bd) ((bd)->getscl((bd)->data))
#define WIRE_ATTRIBUTE(wire) \
static int fops_##wire##_get(void *data, u64 *val) \
{ \
struct i2c_gpio_private_data *priv = data; \
i2c_lock_adapter(&priv->adap); \
*val = get##wire(&priv->bit_data); \
i2c_unlock_adapter(&priv->adap); \
return 0; \
} \
static int fops_##wire##_set(void *data, u64 val) \
{ \
struct i2c_gpio_private_data *priv = data; \
i2c_lock_adapter(&priv->adap); \
set##wire(&priv->bit_data, val); \
i2c_unlock_adapter(&priv->adap); \
return 0; \
} \
DEFINE_DEBUGFS_ATTRIBUTE(fops_##wire, fops_##wire##_get, fops_##wire##_set, "%llu\n")
static int fops_incomplete_transfer_set(void *data, u64 addr)
struct i2c_gpio_private_data *priv = data;
struct i2c_algo_bit_data *bit_data = &priv->bit_data;
int i, pattern;
if (addr > 0x7f)
return -EINVAL;
/* ADDR (7 bit) + RD (1 bit) + SDA hi (1 bit) */
pattern = (addr << 2) | 3;
/* START condition */
setsda(bit_data, 0);
/* Send ADDR+RD, request ACK, don't send STOP */
for (i = 8; i >= 0; i--) {
setscl(bit_data, 0);
udelay(bit_data->udelay / 2);
setsda(bit_data, (pattern >> i) & 1);
udelay((bit_data->udelay + 1) / 2);
setscl(bit_data, 1);
return 0;
DEFINE_DEBUGFS_ATTRIBUTE(fops_incomplete_transfer, NULL, fops_incomplete_transfer_set, "%llu\n");
static void i2c_gpio_fault_injector_init(struct platform_device *pdev)
struct i2c_gpio_private_data *priv = platform_get_drvdata(pdev);
* If there will be a debugfs-dir per i2c adapter somewhen, put the
* 'fault-injector' dir there. Until then, we have a global dir with
* all adapters as subdirs.
if (!i2c_gpio_debug_dir) {
i2c_gpio_debug_dir = debugfs_create_dir("i2c-fault-injector", NULL);
if (!i2c_gpio_debug_dir)
priv->debug_dir = debugfs_create_dir(pdev->name, i2c_gpio_debug_dir);
if (!priv->debug_dir)
debugfs_create_file_unsafe("scl", 0600, priv->debug_dir, priv, &fops_scl);
debugfs_create_file_unsafe("sda", 0600, priv->debug_dir, priv, &fops_sda);
debugfs_create_file_unsafe("incomplete_transfer", 0200, priv->debug_dir,
priv, &fops_incomplete_transfer);
static void i2c_gpio_fault_injector_exit(struct platform_device *pdev)
struct i2c_gpio_private_data *priv = platform_get_drvdata(pdev);
static inline void i2c_gpio_fault_injector_init(struct platform_device *pdev) {}
static inline void i2c_gpio_fault_injector_exit(struct platform_device *pdev) {}
static void of_i2c_gpio_get_props(struct device_node *np,
struct i2c_gpio_platform_data *pdata)
......@@ -228,6 +335,8 @@ static int i2c_gpio_probe(struct platform_device *pdev)
? ", no clock stretching" : "");
return 0;
......@@ -236,6 +345,8 @@ static int i2c_gpio_remove(struct platform_device *pdev)
struct i2c_gpio_private_data *priv;
struct i2c_adapter *adap;
priv = platform_get_drvdata(pdev);
adap = &priv->adap;
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