How to describe i2c switch in json file

[znning]

How to describe below i2c topology in json file?

i2c-0------- |--------------------|
             | PCA9548         ch0|----emc1413
             |                 ch1|----ina219
reset_pin----|--------------------|

[edineshkumar]

Need to configure Mux in kernel device tree and then you can use corresponded bus number and slave address in json file I guess.

Below is the reference for to configure Mux in DT.

https://github.com/openbmc/linux/blob/dev-6.1/arch/arm/boot/dts/aspeed-bmc-facebook-fuji.dts

[saipavann27]

There is Two ways to configure the Mux (PCA9548) Connected End devices (Ex: emc1413 (Temp sensor), ina219 (adc)) in the Json file.

Ex: i2c0 (Master) --> Mux (PCA9548) --> channel-0 (emc1413)
--> channel-1 (ina219)
--> channel 2,3,4,5,6,7.

                                       1. Static Method.
                                       2. Dynamic Method.

Note: Before configuring the json file in application level. Need to Modify the required board specific file (dts) and need add the specific Mux driver and In Each channel, need to add the required End Device. Below is the reference for to configure Mux in DT.

        Link: https://github.com/openbmc/linux/blob/dev-6.1/arch/arm/boot/dts/aspeed-bmc-facebook-fuji.dts

1. Static Method:

                   This Method does not require the eeprom configuration. we will mention PROBE type true in json and will hardcode the bus number in the json for each device.
   
                  Example Json: 
                                                  {
                                                      "Exposes": [
                                                             {
                                                                 "Address": "<Device Adress>",
                                                                 "Bus": "<Bus Number>", /* Bus Need to check and confirm Every time  */
                                                                 "Name": "<Device Name>",
                                                                 "Type": "<Device Type>" /* Ex: "TYPE":"ADC" For ADC Sensor */
                                                             },
                                                             {
                                                                   /* Other Devices */
                                                             }
                                                        ],
                                                       "Name": "<Name of the Board>",
                                                       "Probe": "TRUE", /* Hardcoding to Probe type TRUE */
                                                       "Type": "Board"
                                                  }
   

2. Dynamic Method:

                           This method requires an eeprom device configuration and we will configure the json with PROBE. Based on probe we will dynamically assigned bus numbers for End devices
   
                       Example Json: 
                                                   {
                                                       "Exposes": [
                                                              {
                                                                   "Address": "$address", /* Bus Address we will get if device is detected by HW */
                                                                    "Bus": "$bus", /* Bus Number we will get if device is detected by HW */
                                                                   "Name": "<Name of the Device>",
                                                                   "Type": "EEPROM"
                                                              },
                                                              {
                                                                  "Address": "<Device Adress>",
                                                                  "Bus": "$bus+1", /* Device bus number under the channel 1 */  
                                                                  "Name": "<Device Name>",
                                                                  "Type": "<Device Type>" /* Ex: "TYPE":"ADC" For ADC Sensor */
                                                              },
                                                               {
                                                                  "Address": "<Device Adress>",
                                                                  "Bus": "$bus+4", /* Device bus number under the channel 4 */  
                                                                  "Name": "<Device Name>",
                                                                  "Type": "<Device Type>" /* Ex: "TYPE":"ADC" For ADC Sensor */
                                                              },
                                                              {
                                                                    /* Other Devices */
                                                              }
                                                         ],
                                                        "Name": "<Name of the Board>",
                                                       "Probe": "xyz.openbmc_project.FruDevice({'BOARD_PRODUCT_NAME': '<NAME>'})",
                                                        "Type": "Board"
                                                   }
   

[saipavann27]

Please refer this for detail documentation: https://gerrit.openbmc.org/c/openbmc/entity-manager/+/85577