diff options
author | Jens Axboe <axboe@kernel.dk> | 2018-02-05 12:55:38 -0700 |
---|---|---|
committer | Jens Axboe <axboe@kernel.dk> | 2018-02-05 12:55:38 -0700 |
commit | 9e05c864993c5442227f83ae1694a737d7a102ed (patch) | |
tree | e35b60bb3c0c179f147e9acaad5444f1e5d9117e /Documentation/i2c/gpio-fault-injection | |
parent | 3c15f3f545afa320c5e3822825a9a53c664776b6 (diff) | |
parent | 35277995e17919ab838beae765f440674e8576eb (diff) |
Merge branch 'master' into test
* master: (688 commits)
dt-bindings: mailbox: qcom: Document the APCS clock binding
mailbox: qcom: Create APCS child device for clock controller
mailbox: qcom: Convert APCS IPC driver to use regmap
KVM/SVM: Allow direct access to MSR_IA32_SPEC_CTRL
KVM/VMX: Allow direct access to MSR_IA32_SPEC_CTRL
KVM/VMX: Emulate MSR_IA32_ARCH_CAPABILITIES
KVM/x86: Add IBPB support
KVM/x86: Update the reverse_cpuid list to include CPUID_7_EDX
pinctrl: remove include file from <linux/device.h>
firmware: dmi: handle missing DMI data gracefully
firmware: dmi_scan: Fix handling of empty DMI strings
firmware: dmi_scan: Drop dmi_initialized
firmware: dmi: Optimize dmi_matches
Revert "defer call to mem_cgroup_sk_alloc()"
soreuseport: fix mem leak in reuseport_add_sock()
net: qlge: use memmove instead of skb_copy_to_linear_data
net: qed: use correct strncpy() size
net: cxgb4: avoid memcpy beyond end of source buffer
cls_u32: add missing RCU annotation.
r8152: set rx mode early when linking on
...
Diffstat (limited to 'Documentation/i2c/gpio-fault-injection')
-rw-r--r-- | Documentation/i2c/gpio-fault-injection | 54 |
1 files changed, 54 insertions, 0 deletions
diff --git a/Documentation/i2c/gpio-fault-injection b/Documentation/i2c/gpio-fault-injection new file mode 100644 index 000000000000..e0c4f775e239 --- /dev/null +++ b/Documentation/i2c/gpio-fault-injection @@ -0,0 +1,54 @@ +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. + +"scl" +----- + +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 +layers. + +"sda" +----- + +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. + +"incomplete_transfer" +--------------------- + +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. |