Add a fault injector simulating 'arbitration lost' from multi-master
setups. Read the docs for its usage.
A helper function for future fault injectors using SCL interrupts is
created to achieve this.
Signed-off-by: Wolfram Sang <wsa+rene...@sang-engineering.com>
---
Change since RFC:
* user supplied value is now duration of interference instead of number of
interferences
* refactored code to suppy a resusable helper function to install SCL interrupt
handlers
* added error checks to interrupt number
* slightly renamed the SCL interrupt when registering
Thanks again, Geert, for the review!
Documentation/i2c/gpio-fault-injection | 25 ++++++++++++
drivers/i2c/busses/i2c-gpio.c | 71 ++++++++++++++++++++++++++++++++++
2 files changed, 96 insertions(+)
diff --git a/Documentation/i2c/gpio-fault-injection
b/Documentation/i2c/gpio-fault-injection
index 1a44e3edc0c4..5262801438e6 100644
--- a/Documentation/i2c/gpio-fault-injection
+++ b/Documentation/i2c/gpio-fault-injection
@@ -83,3 +83,28 @@ This is why bus recovery (up to 9 clock pulses) must either
check SDA or send
additional STOP conditions to ensure the bus has been released. Otherwise
random data will be written to a device!
+Lost arbitration
+================
+
+Here, we want to simulate the condition where the master under tests loses the
+bus arbitration against another master in a multi-master setup.
+
+"lose_arbitration"
+------------------
+
+This file is write only and you need to write the duration of the arbitration
+interference (in us). The calling process will then sleep and wait for the
+next bus clock. The process is interruptible, though.
+
+Arbitration lost is achieved by waiting for SCL going down by the master under
+test and then pulling SDA low for some time. So, the I2C address sent out
+should be corrupted and that should be detected properly. That means that the
+address sent out should have a lot of '1' bits to be able to detect corruption.
+There doesn't need to be a device at this address because arbitration lost
+should be detected beforehand. Also note, that SCL going down is monitored
+using interrupts, so the interrupt latency might cause the first bits to be not
+corrupted. A good starting point for using this fault injector on an otherwise
+idle bus is:
+
+# echo 200 > lose_arbitration &
+# i2cget -y <bus_to_test> 0x3f
diff --git a/drivers/i2c/busses/i2c-gpio.c b/drivers/i2c/busses/i2c-gpio.c
index 2d532cc042f5..f3645148d120 100644
--- a/drivers/i2c/busses/i2c-gpio.c
+++ b/drivers/i2c/busses/i2c-gpio.c
@@ -7,12 +7,14 @@
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
+#include <linux/completion.h>
#include <linux/debugfs.h>
#include <linux/delay.h>
#include <linux/gpio/consumer.h>
#include <linux/i2c-algo-bit.h>
#include <linux/i2c.h>
#include <linux/init.h>
+#include <linux/interrupt.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/platform_data/i2c-gpio.h>
@@ -27,6 +29,9 @@ struct i2c_gpio_private_data {
struct i2c_gpio_platform_data pdata;
#ifdef CONFIG_I2C_GPIO_FAULT_INJECTOR
struct dentry *debug_dir;
+ /* these must be protected by bus lock */
+ struct completion scl_irq_completion;
+ u64 scl_irq_data;
#endif
};
@@ -162,6 +167,67 @@ static int fops_incomplete_write_byte_set(void *data, u64
addr)
}
DEFINE_DEBUGFS_ATTRIBUTE(fops_incomplete_write_byte, NULL,
fops_incomplete_write_byte_set, "%llu\n");
+static int i2c_gpio_fi_act_on_scl_irq(struct i2c_gpio_private_data *priv,
+ irqreturn_t handler(int, void*))
+{
+ int ret, irq = gpiod_to_irq(priv->scl);
+
+ if (irq < 0)
+ return irq;
+
+ i2c_lock_bus(&priv->adap, I2C_LOCK_ROOT_ADAPTER);
+
+ ret = gpiod_direction_input(priv->scl);
+ if (ret)
+ goto unlock;
+
+ reinit_completion(&priv->scl_irq_completion);
+
+ ret = request_irq(irq, handler, IRQF_TRIGGER_FALLING,
+ "i2c_gpio_fault_injector_scl_irq", priv);
+ if (ret)
+ goto output;
+
+ wait_for_completion_interruptible(&priv->scl_irq_completion);
+
+ free_irq(irq, priv);
+ output:
+ ret = gpiod_direction_output(priv->scl, 1);
+ unlock:
+ i2c_unlock_bus(&priv->adap, I2C_LOCK_ROOT_ADAPTER);
+
+ return ret;
+}
+
+static irqreturn_t lose_arbitration_irq(int irq, void *dev_id)
+{
+ struct i2c_gpio_private_data *priv = dev_id;
+
+ setsda(&priv->bit_data, 0);
+ udelay(priv->scl_irq_data);
+ setsda(&priv->bit_data, 1);
+
+ complete(&priv->scl_irq_completion);
+
+ return IRQ_HANDLED;
+}
+
+static int fops_lose_arbitration_set(void *data, u64 duration)
+{
+ struct i2c_gpio_private_data *priv = data;
+
+ priv->scl_irq_data = duration;
+ /*
+ * Interrupt on falling SCL. This ensures that the master under test has
+ * really started the transfer. Interrupt on falling SDA did only
+ * exercise 'bus busy' detection on some HW but not 'arbitration lost'.
+ * Note that the interrupt latency may cause the first bits to be
+ * transmitted correctly.
+ */
+ return i2c_gpio_fi_act_on_scl_irq(priv, lose_arbitration_irq);
+}
+DEFINE_DEBUGFS_ATTRIBUTE(fops_lose_arbitration, NULL,
fops_lose_arbitration_set, "%llu\n");
+
static void i2c_gpio_fault_injector_init(struct platform_device *pdev)
{
struct i2c_gpio_private_data *priv = platform_get_drvdata(pdev);
@@ -181,10 +247,15 @@ static void i2c_gpio_fault_injector_init(struct
platform_device *pdev)
if (!priv->debug_dir)
return;
+ init_completion(&priv->scl_irq_completion);
+
debugfs_create_file_unsafe("incomplete_address_phase", 0200,
priv->debug_dir,
priv, &fops_incomplete_addr_phase);
debugfs_create_file_unsafe("incomplete_write_byte", 0200,
priv->debug_dir,
priv, &fops_incomplete_write_byte);
+ if (priv->bit_data.getscl)
+ debugfs_create_file_unsafe("lose_arbitration", 0200,
priv->debug_dir,
+ priv, &fops_lose_arbitration);
debugfs_create_file_unsafe("scl", 0600, priv->debug_dir, priv,
&fops_scl);
debugfs_create_file_unsafe("sda", 0600, priv->debug_dir, priv,
&fops_sda);
}
--
2.11.0
