1# Voltage Regulator Configuration 2 3Author: Shawn McCarney (Discord ShawnMcCarney) 4 5Primary assignee: Shawn McCarney 6 7Other contributors: Derek Howard (Discord derekh55), Matt Spinler (Discord mspinler) 8 9Created: 2019-07-13 10 11 12## Problem Description 13[Voltage regulators][1] have many configurable properties such as output 14voltage, over-current limit, and pgood thresholds. The configuration is often 15dependent on the system type and rail type. Regulators have a hardware default 16configuration that is defined by hardware engineers early in system design. 17However, this default configuration sometimes must be modified by firmware. A 18new application is needed to configure regulators. It should be data-driven to 19support a variety of regulator types and to avoid hard-coded logic. 20 21 22## Background and References 23 24### Regulator Configuration Data ("Config File") 25Hardware engineers must specify many low-level configuration values for a 26regulator. Some simple examples include output voltage, over-current limit, 27and pgood thresholds. These values often vary depending on the system type and 28rail type. 29 30Depending on the regulator type, the hardware engineer may enter the 31configuration values into a tool that produces a "config file". 32 33The regulator configuration information is sent to manufacturing and stored in 34non-volatile memory on the regulator. This provides the hardware/power-on 35default configuration. 36 37The default configuration values often need to be changed later. This can be 38due to factors such as the following: 39* New information found during hardware testing. For example, downstream 40 hardware requires a higher voltage or is drawing more current than expected. 41* Hardware workarounds. Problems in the regulator hardware or related hardware 42 sometimes require new configuration values to work around the issue. The 43 problem may be resolved in newer versions of the hardware, but firmware still 44 must support the older hardware. For this reason, hardware workarounds are 45 sometimes conditional, applied only to regulators with a certain version 46 register value or [Vital Product Data (VPD)][2] keyword value. 47* Improve manufacturing yields. Sometimes regulator configuration values must 48 be changed to allow more hardware to pass manufacturing tests. For example, 49 the voltage may need to be increased to overcome minor manufacturing defects. 50 51### OpenBMC Regulator Configuration Scripts 52Regulator configuration changes are performed on some OpenBMC systems using 53shell scripts. For example, the following scripts configure regulators on 54Witherspoon systems: 55* [vrm-control.sh][3] 56* [power-workarounds.sh][4] 57 58### Hwmon and IIO Device Driver Frameworks 59The Linux [Hardware Monitoring Kernel API (hwmon)][5] and [Industrial I/O 60Subsystem (IIO)][6] provide device driver frameworks for monitoring hardware 61and making sensor values available to applications. They do not provide an 62interface for performing low-level regulator configuration. 63 64### Voltage and Current Regulator Device Framework 65The Linux [Voltage and Current Regulator API][7] provides a device driver 66framework for voltage and current regulators. It provides a mechanism for the 67device drivers of "consumer" devices to request a voltage or current level from 68the regulator. It does not provide an interface for performing low-level 69regulator configuration. 70 71 72## Requirements 73* Provide ability to modify configuration of any voltage regulator with a PMBus 74 or I2C connection to the BMC. 75* Apply the configuration changes early in the boot before the regulators are 76 enabled. 77* If an error occurs trying to configure a regulator, log the error and 78 continue with the next regulator. 79* Read configuration changes from a data file that is read at run-time. 80* Provide a method for testing new configuration changes by copying a new data 81 file to the BMC. 82 83### Non-Requirements 84* Enable/disable voltage regulators and monitor their pgood signals. 85 * This is handled by the power sequencer chip and related firmware. 86* Modify regulator configuration after regulator has been enabled. 87 * Modifying regulator configuration while the system is running 88 is often done by the host using a different bus connection. 89* Validate that the correct number and types of regulators are present in the 90 system. 91* Concurrent maintenance or hot-plugging of regulators, where a regulator is 92 removed/added/replaced while the system is running. 93 94 95## Proposed Design 96 97### Application 98A new application named `phosphor-regulators` will be created to configure 99voltage regulators. The application will be located in the proposed new 100`phosphor-power` repository. 101 102*Statement of direction: This application will provide other regulator-based 103functionality in the future, such as detecting redundant phase faults.* 104 105### Application Data File 106The application will read a JSON file at runtime that defines the configuration 107changes for all regulators. The JSON file will be specific to a system type, 108so it will be stored in the GitHub repository for the appropriate build layer 109(such as meta-ibm). 110 111JSON file location on the BMC: 112* Standard directory: `/usr/share/phosphor-regulators` (read-only) 113* Test directory: `/etc/phosphor-regulators` (writable) 114 115A new version of the JSON file can be tested by copying it to the test 116directory. The application will search both directories, and the file in the 117test directory will override the file in the standard directory. If the 118application receives a SIGHUP signal, it will re-read the JSON file. 119 120A document will be provided that describes the objects and properties that can 121appear in the JSON file. A validation tool will also be provided to verify the 122syntax and contents of the JSON file. 123 124*Statement of direction: This JSON file will be used in the future to define 125other regulator operations, such as how to detect a redundant phase fault.* 126 127### D-Bus Interfaces 128The following new D-Bus interface will be created: 129* Name: `xyz.openbmc_project.Regulator.Collection.Configure` 130* Description: Configures all voltage regulators. 131* Properties: None 132* Methods: Configure() 133 134*Statement of direction: New interfaces that apply to all regulators would use 135the same xyz.openbmc_project.Regulator.Collection namespace. New interfaces 136that apply to a single regulator would use the xyz.openbmc_project.Regulator 137namespace.* 138 139### D-Bus Paths 140The new `xyz.openbmc_project.Regulator.Collection.Configure` interface will be 141implemented on the object path `/xyz/openbmc_project/regulators`. 142 143*Statement of direction: New interfaces that apply to all regulators would be 144implemented on the same object path. Individual regulators would be 145represented by the object path 146`/xyz/openbmc_project/regulators/<regulator_name>`, and interfaces that apply 147to a single regulator would be implemented on that path.* 148 149### Systemd 150The application will be started using systemd when the BMC is at standby. The 151service file will be named `xyz.openbmc_project.Regulators.service`. 152 153During the boot when the chassis is being powered on, the Configure() method on 154the new `xyz.openbmc_project.Regulator.Collection.Configure` interface will be 155called. This must be done prior to the systemd target that enables the 156regulators (powers them on). 157 158### Regulator Device Interface 159The application will communicate with the voltage regulators directly using the 160[i2c-dev][8] userspace I2C interface. Direct communication will be used rather 161than device drivers because the current Linux device driver frameworks do not 162provide the necessary functionality. See the [Alternatives 163Considered](#alternatives-considered) section for more information. 164 165Voltage regulators that are configured using this application will not be bound 166to device drivers in the Linux device tree. When the system is powered on, the 167application will obtain the regulator sensor values and store them on D-Bus in 168the same format as `phosphor-hwmon`. 169 170*Statement of direction: If a driver framework is developed in the future that 171supports low-level regulator configuration, then this application will be 172enhanced to utilize those drivers. The goal is for the application to support 173a flexible device interface, where drivers are used if possible and i2c-dev is 174used if necessary.* 175 176 177## Alternatives Considered 178 179### Using Standard Linux Device Drivers to Configure Regulators 180Ideally one of the following device driver frameworks could be used rather than 181i2c-dev to configure the regulators: 182* [Hardware Monitoring Kernel API][5] 183* [Industrial I/O Subsystem][6] 184* [Voltage and Current Regulator API][7] 185 186Unfortunately none of these provide the required functionality: 187* Ability to perform system-specific and rail-specific, low-level 188 configuration. 189* Ability to perform dynamic configuration based on regulator version register 190 values or [VPD][2] values. 191* Ability to test new configuration values iteratively and quickly without 192 needing to modify a device driver or rebuild the kernel. 193 194A meeting was held with Joel Stanley and Andrew Jeffery to discuss this issue. 195They believe long term a new driver framework could be designed that would 196provide this functionality and would be acceptable to the Linux upstream 197community. If this occurs, this application will be modified to utilize the 198new driver framework rather than performing direct I2C communication from 199userspace. 200 201### Using Shell Scripts to Configure Regulators 202Currently shell scripts are used to configure regulators on some OpenBMC 203systems, such as Witherspoon. During boot, the shell scripts unbind device 204drivers, perform `i2cset` commands to configure regulators, and then re-bind 205device drivers. 206 207Using shell scripts has the following disadvantages: 208* Typically no error checking is performed to verify the `i2cset` command 209 worked. If error checking were added based on return code, it would be 210 difficult to log an appropriate error with all the necessary information. 211* On a large system with many regulators and register updates, a shell 212 script would run more slowly than an application and negatively impact boot 213 speed. Each `i2cset` command requires starting a separate child process. 214* Scripts are usually hard-coded to one system type and do not provide a 215 common, data-driven solution. 216 217 218## Impacts 219* No major impacts are expected to existing APIs, security, documentation, 220 performance, or upgradability. 221* The new D-Bus interface is documented in the [Proposed 222 Design](#proposed-design) section. 223* The application should be able to configure regulators using 224 i2c-dev as fast or faster than equivalent shell scripts using `i2cset`. 225* The regulator sensor values will be stored on D-Bus in a way that is 226 consistent with `phosphor-hwmon`. 227 228 229## Testing 230* Automated test cases will be written to test as much of the application code 231 as possible. 232* A mock device interface will be used to test that the correct I2C reads and 233 writes are occurring without accessing real hardware. 234* End-to-end boot testing will be performed to ensure that the correct I2C 235 reads/writes occurred, that the system boots, and that no errors occur. 236* CI tests that boot a system will indirectly test this application. 237 238 239[1]: https://en.wikipedia.org/wiki/Voltage_regulator_module 240[2]: https://en.wikipedia.org/wiki/Vital_Product_Data 241[3]: https://github.com/openbmc/meta-ibm/blob/master/meta-witherspoon/recipes-phosphor/chassis/vrm-control/vrm-control.sh 242[4]: https://github.com/openbmc/meta-ibm/blob/master/meta-witherspoon/recipes-phosphor/chassis/power-workarounds/witherspoon/power-workarounds.sh 243[5]: https://www.kernel.org/doc/html/latest/hwmon/hwmon-kernel-api.html 244[6]: https://www.kernel.org/doc/html/latest/driver-api/iio/index.html 245[7]: https://www.kernel.org/doc/html/latest/driver-api/regulator.html 246[8]: https://www.kernel.org/doc/Documentation/i2c/dev-interface 247