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
