Hi Simon,
Am 2020-11-30 02:53, schrieb Simon Glass:
At present each device has two sequence numbers, with 'req_seq' being set up at bind time and 'seq' at probe time. The idea is that devices can 'request' a sequence number and then the conflicts are resolved when the device is probed.
This makes things complicated in a few cases, since we don't really know (at bind time) what the sequence number will end up being. We want to honour the bind-time requests if at all possible, but in fact the only source of these at present is the devicetree aliases.
Apart from the obvious need for sequence numbers to supports U-Boot's numbering on devices on the command line, the current scheme was designed to:
- avoid calculating the sequence number until it is needed, to save execution time
- allow multiple devices to obtain a particular sequence number as they are probed and removed
- retain a record of the 'requested' sequence number even if it turns
out that a device could not get it (to allow debugging and retrying)
After some years using the current scheme it seems on balance that these goals don't have as much merit as first thought. The first point would be persuasive except that we end up reading the devicetree aliases at bind-time anyway. So the work of resolving the sequence numbers during probing is not that great. The second point hasn't really been an issue, as there is typically no contention for sequence numbers (boards tend to allocate them statically in the devicetree). Re the third point, we can often figure out what was requested by looking at aliases, and in the cases where we can't, it doesn't seem to matter much.
Since we have the devicetree available at bind time, we may as well just use it, in the hope that the required processing will turn out to be useful later (i.e. the device actually gets used). In addition, it is simpler to use a single sequence number, since it avoids confusion and some extra code.
This series moves U-Boot to use a single, bind-time sequence number. All uclasses with the DM_UC_FLAG_SEQ_ALIAS flag enabled will assign sequence numbers to their devices, so that as soon as a device is bound, it has a sequence number. If a devicetree alias provides the number, it will be used. Otherwise, during initial binding, the first free number is used.
What does "first free number mean"?
I have a device tree with the following aliases for network:
aliases { ethernet0 = &enetc0; ethernet1 = &enetc1; ethernet2 = &enetc2; ethernet3 = &enetc6; };
The individual devices might be disabled, depending on the board variant (which might also be dynamically determined during startup).
My first smoke test with this series show the following:
uclass 32: eth 0 * enetc-0 @ ffd40e60, seq 0 1 * ax88179_eth @ ffd51f50, seq 1
Looks like the usb ethernet device will get seq 1 assigned (after "usb start"). Is this intended?
If so, this is a problem, because for ethernet devices, the MAC address is assigned according to the ethNaddr variable. And at least for this board (kontron_sl28) the first four are reserved for the ones with the alias entries. Thus I'd have expected that the usb device will get seq 4 assigned.
For ad-hoc calls to device_bind() afterwards (e.g. from driver code), the sequence is set to the maximum sequence number for the uclass + 1.
Apart from the simplicity gains, overall these changes seem to reduce the number of tweaks and workarounds needed to get the desired behaviour.
However there will certainly be some problems created, so board maintainers should test this out.
-michael