On Tue, Aug 17, 2021 at 11:19 PM Matt Johnston <matt@xxxxxxxxxxxxxxxxxxxx> wrote: > > On Tue, 2021-08-17 at 16:06 -0500, Rob Herring wrote: > On Mon, Aug 16, 2021 at 03:32:40PM +0800, Matt Johnston wrote: > > > .-------. > > > |eeprom | > > > .----------. .------. /'-------' > > > > adapter | | mux --@0,i2c5------' > > > > i2c1 |-.-| --@1,i2c6--.--. > > > > ..........| \'------' \ \ ......... > > > > mctp-i2c | \ \ \ .mctpB . > > > > slave | \ \ '.0x30 . > > > > 0x50 | \ ......... \ '.......' > > > '----------' \ .mctpA . \ ......... > > > '.0x1d . '.mctpC . > > > '.......' '.0x31 . > > > '.......' > > > > > > > I guess 'mctp-i2c' alone here is fine given it's the I2C controller > > slave implementation which is just a protocol. It's the external devices > > where my concern is. > > > > Though, don't you need a different compatible for it and external > > devices? > > We are only defining a binding for the system's own MCTP "controller" > here, not the external devices on the other side of the I2C link. Those are > probed outside of DT, for example hotplug NVMe disks can expose MCTP-over- > I2C. > > This ends up describing something like a network interface, which > happens to use I2C as a transport in this case. (There are other > transports like MCTP-over-serial, but those don't require DT topology > data). For other network-type DT bindings (say, ethernet@), we don't > describe remote network endpoints either, so we're proposing the same > pattern for MCTP. When a switch becomes integrated in, we do. > > > reg = <(0x50 | I2C_OWN_SLAVE_ADDRESS)>; > > > attach-bus = <&i2c1 &i2c6>; > > > > Why do you need to say you are attached to yourself? > > This indicates that the top-level MCTP controller needs to talk to MCTP > endpoints, eg mctpA on the directly attached bus i2c1. In some topologies > there will be no directly-attached endpoints, in which case we would omit > i2c1 from the list. We need to specify the attach-bus property since we > don't have a list of external device endpoints to walk. Okay, so it's a 'what I2C buses should be scanned for MCTP devices'. Why can't that just be all the buses under i2c1 in this example? Limiting it seems like an optimization only. You don't know the endpoint addresses, so you are scanning the whole bus, right? In any case, 'attach-bus' sounds very generic and I'm not sure this is. I'd like to hear from others familiar with I2C on this aspect at least. > [In the case of not directly attached, we still need to plant the mctp-i2c@ > node at the root controller level, as the claimed client address (in reg) > is global across the entire bus. The attach-bus list gives us the set of > interfaces that are necessary for the OS to control] > > > > Regarding I2C_OWN_SLAVE_ADDRESS validation > > You'll have to do a minimum/maximum range with the high bit set and > > addresses 0-7f. > > OK, that will work fine for our binding. The general I2C slave client case > would also have to allow for I2C_TEN_BIT_ADDRESS (1<<31), but MCTP-over-I2C > only accepts 7 bit. TBC, requiring I2C_OWN_SLAVE_ADDRESS being set is specific to MCTP-over-I2C and also serves to document the binding is only for the host side. Rob
