Re: Another problem with I2C multiplexer bus naming

[Danielle Costantino <danielle.costantino-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Try lsi2c on your system and see if the "PATHs" are unique.

on github: https://github.com/costad2/i2cdev

This should provide you with a unique and unchanging path for all of
you i2c devices.

Then when the conflicting/inconsistent bus appears its path will not
change even if its i2c-%d changes.

- Danielle


On Wed, Mar 11, 2015 at 9:11 PM, Bob Feretich
<bob.feretich-8wbKi1faPaosQv5ZqcSHkQ@public.gmane.org> wrote:
> I am working on a BeagleBone Black (BBB) Cape that contains a PCA9548 multiplexer (mux). The BBB uses two I2C buses, i2c-0 for power management and i2c-2 for Cape discovery and other general use. I have created a dtsi file to describe the mux on my Cape per the Linux Documentation instructions.
>
>
> ...
>
> &i2c2 {
>     i2cmux@77 {
>          compatible = "nxp,pca9548";
>          #address-cells = <1>;
>          #size-cells = <0>;
>          reg = <0x77>;
> };
> ...
>
> When I boot Linux (3.14 kernel) without the cape attached I see i2c-0 and i2c-2...
> ubuntu@arm:~$ ls /dev/i2*
> /dev/i2c-0  /dev/i2c-2
> ubuntu@arm:~$ i2cdetect -l
> i2c-0    i2c           OMAP I2C adapter                    I2C adapter
> i2c-2    i2c           OMAP I2C adapter                    I2C adapter
>
> But, I can also see in dmesg that i2c-0 probing is deferred until after i2c-2.
> [    2.186756] omap_i2c 44e0b000.i2c: could not find pctldev for node /pinmux@44e10800/pinmux_i2c0_pins, deferring probe
> [    2.186803] platform 44e0b000.i2c: Driver omap_i2c requests probe deferral
> [    2.193949] omap_i2c 4819c000.i2c: bus 2 rev0.11 at 100 kHz
> ...snipped...
> [    2.965899] tps65217 0-0024: TPS65217 ID 0xe version 1.2
> [    2.967376] at24 0-0050: 32768 byte 24c256 EEPROM, writable, 1 bytes/write
> [    2.967500] omap_i2c 44e0b000.i2c: bus 0 rev0.11 at 400 kHz
>
>
> This causes a problem when I boot with the Cape attached.
> 1) Probing is deferred on i2c-0.
> 2) i2c-2 is probed, the mux is discovered, and the child buses are
>
>     assigned i2c-0, i2c-1, and i2c-3 through i2c-8.
> 3) The original i2c-0 bus is then probed, but since it requires the name i2c-0 and that name is already used, adapter addition fails.
>
> ubuntu@arm:~$ ls /dev/i2*
> /dev/i2c-0  /dev/i2c-2  /dev/i2c-4  /dev/i2c-6  /dev/i2c-8
> /dev/i2c-1  /dev/i2c-3  /dev/i2c-5  /dev/i2c-7
> ubuntu@arm:~$ i2cdetect -l
> i2c-0    i2c           i2c-2-mux (chan_id 0)               I2C adapter
> i2c-1    i2c           i2c-2-mux (chan_id 1)               I2C adapter
> i2c-2    i2c           OMAP I2C adapter                    I2C adapter
> i2c-3    i2c           i2c-2-mux (chan_id 2)               I2C adapter
> i2c-4    i2c           i2c-2-mux (chan_id 3)               I2C adapter
> i2c-5    i2c           i2c-2-mux (chan_id 4)               I2C adapter
> i2c-6    i2c           i2c-2-mux (chan_id 5)               I2C adapter
> i2c-7    i2c           i2c-2-mux (chan_id 6)               I2C adapter
> i2c-8    i2c           i2c-2-mux (chan_id 7)               I2C adapter
>
>
> From dmesg...
> [    2.186754] omap_i2c 44e0b000.i2c: could not find pctldev for node /pinmux@44e10800/pinmux_i2c0_pins, deferring probe
> [    2.186802] platform 44e0b000.i2c: Driver omap_i2c requests probe deferral
> [    2.193953] omap_i2c 4819c000.i2c: bus 2 rev0.11 at 100 kHz
> ...snipped...
> [    2.753254] i2c /dev entries driver
> [    2.756232] i2c i2c-2: Added multiplexed i2c bus 0
> [    2.756992] i2c i2c-2: Added multiplexed i2c bus 1
> [    2.757690] i2c i2c-2: Added multiplexed i2c bus 3
> [    2.758361] i2c i2c-2: Added multiplexed i2c bus 4
> [    2.759065] i2c i2c-2: Added multiplexed i2c bus 5
> [    2.759717] i2c i2c-2: Added multiplexed i2c bus 6
> [    2.760392] i2c i2c-2: Added multiplexed i2c bus 7
> [    2.761065] i2c i2c-2: Added multiplexed i2c bus 8
> [    2.761081] pca954x 2-0077: registered 8 multiplexed busses for I2C switch
>
> ...snipped...
> [    2.951717] omap_i2c 44e0b000.i2c: failure adding adapter
> ...snipped...
> [    2.964249] omap_i2c: probe of 44e0b000.i2c failed with error -16
> ... snipped ...
> [    8.997764] cpu cpu0: of_pm_voltdm_notifier_register: Failed to get cpu0 regulator/voltdm: -517
> [    8.997796] cpu cpu0: cpu0 clock notifier not ready, retry
> [    9.082435] platform cpufreq-cpu0.0: Driver cpufreq-cpu0 requests probe deferral
> [    9.194548] slave hdmi.38: could not get i2c
>
>
> Is there a quick work-around for this problem (prevent deferred probing or defer both bus probes)?
>
> Is there a way that I can force the child buses to use names that don't conflict with BBB predefined buses (perhaps a property or alias in the device tree)?
>
> Will the future "multiple i2c multiplexers on the same bus" solution fix this problem?
>
> Any other ideas for a work around?
>
> Regards,
>
> Bob Feretich
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-- 
- Danielle Costantino