Zephyr SSFC CBI Configuration
The CrOS Board Information CBI feature is enabled with the CONFIG_PLATFORM_EC_CBI_EEPROM Kconfig, as defined in the CBI Configuration.
One of the CBI elements is the Second Source Factory Cache SSFC field. This config is used at run time to select different hardware options or behaviours, and is defined generally on a board by board basis. The SSFC describes later decisions for a board to indicate alternate second sourced hardware stuffing which can be used by the EC to know which drivers to load.
The SSFC block is limited to 32 bits. The 32 bits are divided into individual fields of varying sizes. Each field has defined values that may be set to control the behaviour according to the definition for that board.
Device tree is used to define and specify the field sizes and values.
The SSFC device tree nodes are defined via the cros-ec,cbi-ssfc and cros-ec,cbi-ssfc-value YAML bindings.
The cros-ec,cbi-ssfc bindings define the name and size of each field. The cros-ec,cbi-ssfc-value bindings allow names/values to be defined for each value that may be stored in the field. One of the values may be designated as the default, which is used if the CBI data cannot be accessed.
Spare CBI SSFC fields are always initialised as zeros, so that future fields will have a guaranteed value, so typically a zero value is used as a default, indicating the default field.
An example definition is:
cbi-ssfc {
compatible = "cros-ec,cbi-ssfc";
base_sensor {
enum-name = "BASE_SENSOR";
size = <3>;
base_sensor_0: bmi160 {
compatible = "cros-ec,cbi-ssfc-value";
status = "okay";
value = <1>;
};
};
lid_sensor {
enum-name = "LID_SENSOR";
size = <3>;
lid_sensor_0: bma255 {
compatible = "cros-ec,cbi-ssfc-value";
status = "okay";
value = <1>;
};
};
lightbar {
enum-name = "LIGHTBAR";
size = <2>;
lightbar_0: 10_led {
compatible = "cros-ec,cbi-ssfc-value";
status = "okay";
value = <1>;
};
};
};
To access the presence of an SSFC component, the CBI driver should be used to access the CBI API to check for an SSFC match e.g:
#include "cros_cbi.h"
bool is_base_sensor_bmi160(void)
{
return cros_cbi_ssfc_check_match(
CBI_SSFC_VALUE_ID(DT_NODELABEL(base_sensor_0)));
}
No threads used in this feature.
The ectool cbi command can be used to read and set the SSFC.