On 04/21/2016 04:56 PM, Peter Rosin wrote: > Crestez Dan Leonard wrote: >> On 04/20/2016 11:31 PM, Peter Rosin wrote: >>> Crestez Dan Leonard wrote: >>>> Changes since that version: >>>> * Nest the adapter in inv_mpu6050_state instead of making it static >>>> * Explicitly forward of_node "i2c-aux-master" to allow describing aux devices >>>> via devicetree. >>>> >>>> For bypass/mux mode devicetree works automatically. The forwarding is based on >>>> the "chan_id" parameter to i2c_add_mux_adapter and is implemented here: >>>> >>>> http://lxr.free-electrons.com/source/drivers/i2c/i2c-mux.c?v=4.5#L158 >>>> >>>> Perhaps it might be better for devices handled via master mode to be described >>>> via i2c@1? This would work by scanning the mpu node's children for something >>>> with reg == 1. >>> >>> The 0 in i2c@0 (which is used by the mux mode) is the index of the mux slave >>> meaning that i2c@1 would be a second mux slave on the same mux, but this is >>> not a real mux as such, it is a gate which is piggybacking on the i2c mux infra. >>> So, this "mux" can't have a second slave which is why only 0 is valid. >> >> This behavior is automatic in i2c mux code and seems to assume that all >> the children of mux_dev are i2c muxes. This might be obviously correct >> and useful for dedicated i2c mux devices but in my case mux_dev is just >> the i2c_client for a sensor. >> >> From Documentation/devicetree/bindings/i2c/i2c-mux.txt: >> >>> An i2c bus multiplexer/switch will have several child busses that are >>> numbered uniquely in a device dependent manner. The nodes for an i2c >>> bus multiplexer/switch will have one child node for each child bus. >> >> This seems to be written in a way that would allow me to define the >> "auxiliary i2c master" as bus "1". After all, the numbering is device >> dependent and it's not clear that all the child busses need to be >> accessible through muxing rather than indirect access through device >> registers. > > You are correct that if you have devicetree children where reg does > not match the chan_id given to i2c_add_mux_adapter() those children > will be ignored by the i2c-mux code. So, the code would be happy with > a devicetree such as: > > mpu6050@68 { > compatible = "..."; > reg = <0x68>; > ... > i2c-aux-mux@0 { > #address-cells = <1>; > #size-cells = <0>; > reg = <0>; > > foo@44 { > compatible = "bar"; > reg = <0x44>; > ... > } > } > i2c-aux-master@1 { > #address-cells = <1>; > #size-cells = <0>; > reg = <1>; > > gazonk@44 { > compatible = "baz"; > reg = <0x44>; > ... > } > } > } > > as long as you do only call i2c_add_mux_adapter() with chan_id = 0. And that > is what you are doing. But I think it is a bit subtle... This kind of stuff needs to be written up in Documentation/devicetree/bindings anyway. >>> I think the naming could be i2c-master0, i2c-master1 etc if it, with >>> future work, would be possible to add more than one master (you talked about >>> 5 i2c slaves..). >> >> The device has 5 sets of registers for controlling i2c slaves but only >> one physical auxiliary i2c bus. As far as I can tell slaves 0-3 are >> intended to be used for gathering readings for slaved sensors >> periodically without external intervention. Slave 4 can generate an >> interrupt on completion and is more suitable for general-purpose >> communication with any number of devices. > > Ah, ok, so all 5 sets of slave registers are about the same physical i2c > bus. So, you basically cannot sanely use this physical aux i2c bus as an > i2c-mux and an extra i2c adapter in the same hw design. Correct? You can access devices on the auxiliary i2c bus either through mux-ing or the adapter added by this patch. I think mux mode works better (lower latency) but is not available when the primary connection is via SPI. You can use both but it doesn't particularly make sense. > In that case, couldn't you look at the names of any devicetree children > and use that to decide if you should even attempt to call > i2c_add_mux_adapter or i2c_add_adapter? But the adapter should be added even if nothing is defined for it. Registering i2c clients by echoing in new_device is a valid usecase. What could be done is only register the i2c mux in i2c mode and the i2c master in spi mode and make the bindings identical. > (But please don't clobber stuff for my i2c-mux rework, or you will > have to wait even longer for that deadlock to be resolved) I won't. I should have sent this as an [RFC] anyway, it will take a while to get it. -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
