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Diffstat (limited to 'Documentation/i2c/gpio-fault-injection')
| -rw-r--r-- | Documentation/i2c/gpio-fault-injection | 61 |
1 files changed, 58 insertions, 3 deletions
diff --git a/Documentation/i2c/gpio-fault-injection b/Documentation/i2c/gpio-fault-injection index a4ce62090fd5..c87f416d53dd 100644 --- a/Documentation/i2c/gpio-fault-injection +++ b/Documentation/i2c/gpio-fault-injection @@ -1,3 +1,4 @@ +========================= Linux I2C fault injection ========================= @@ -13,6 +14,9 @@ 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. +Wire states +=========== + "scl" ----- @@ -34,10 +38,10 @@ 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 -following class of fault injectors. +"incomplete transfers" class of fault injectors. -Introduction to incomplete transfers ------------------------------------- +Incomplete transfers +==================== The following fault injectors create situations where SDA will be held low by a device. Bus recovery should be able to fix these situations. But please note: @@ -79,3 +83,54 @@ 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 test 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 +intereference (in µs, maximum is 100ms). 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 + +Panic during transfer +===================== + +This fault injector will create a Kernel panic once the master under test +started a transfer. This usually means that the state machine of the bus master +driver will be ungracefully interrupted and the bus may end up in an unusual +state. Use this to check if your shutdown/reboot/boot code can handle this +scenario. + +"inject_panic" +-------------- + +This file is write only and you need to write the delay between the detected +start of a transmission and the induced Kernel panic (in µs, maximum is 100ms). +The calling process will then sleep and wait for the next bus clock. The +process is interruptible, though. + +Start of a transfer is detected by waiting for SCL going down by the master +under test. A good starting point for using this fault injector is: + +# echo 0 > inject_panic & +# i2cget -y <bus_to_test> <some_address> + +Note that there doesn't need to be a device listening to the address you are +using. Results may vary depending on that, though. |