On 2019-09-30 04:43, Biwen Li wrote: >> >> On 2019-09-29 12:36, Biwen Li wrote: >>> On some Layerscape boards like LS2085ARDB and LS2088ARDB, input >>> pull-up resistors on PCA954x MUX device are missing on board, So, if >>> MUX are disabled after powered-on, input lines will float leading to >>> incorrect functionality. SDA and SCL are not "inputs". They are part of a bus and are both bidirectional signals. Speaking of input signals in an I2C context is ambiguous. >> >> Hi! >> >> Are you saying that the parent bus of the mux is relying on some pull-ups inside >> the mux? > Yes, as follows: > VCC > ------- > |------------------- > | | > \ \ > /10K resister / 10k resister > \ \ > | | > | | > I2C1_SCL ------------------------ I2C1_SCL | ---------------------- > --------------------|SCL | ----------------------------------------|SCL | > I2C1_SDA | PCA9547 | I2C1_SDA | | PCA9547 | > --------------------|SDA | ----------------------------|-----------|SDA | > ------------------------ ---------------------- > --wrong design(need software fix as above or hardware fix)-- --proper design-- Ok, got it (but the "picture" didn't help). >> >>> Hence, PCA954x MUX device should never be turned-off after power-on. >>> >>> Add property to skip disabling PCA954x MUX device if device tree >>> contains "i2c-mux-never-disable" >>> for PCA954x device node. >>> >>> Errata ID: E-00013 on board LS2085ARDB and LS2088ARDB (Board revision >>> found on Rev.B, Rev.C and Rev.D) >> >> I think you should follow the example of the i2c-mux-gpio driver and implement >> the idle-state property instead. >> >> That is a lot more consistent, assuming it solves the problem at hand? > Got it, thanks, I will try it. I'll wait for that patch then, instead of spending more energy on the never-disable approach. Cheers, Peter
