Hi,
On 16-03-15 23:02, Paul Kocialkowski wrote:
Le lundi 16 mars 2015 à 14:45 +0100, Hans de Goede a écrit :
Hi,
On 16-03-15 13:31, Olliver Schinagl wrote:
Hey,
On 16-03-15 10:52, Hans de Goede wrote:
Hi,
Oops, missed a bit to reply to, see below:
On 16-03-15 10:04, Olliver Schinagl wrote:
Also, which part of the SID do we want in /proc/cpuinfo? The one is bigger then
the other, though looking at http://linux-sunxi.org/SID_Register_Guide there's
a lot of non-uniqueness that can be ignored (chip ID (1623 for example).
I would say all of it, serial numbers often also contain
a fixed bit with model info, for /proc/cpuinfo that is fine.
but isn't the serial in /proc/cpuinfo limited to a certain number of bits?
Could be, whomever writes patches for this needs to look into that, and
if necessary truncate the SID somehow.
As far as I can see, the SID has (at least) 4 32bit words. It seems that
there is more on e.g. A20 but those are not always populated, so I think
it's safer to go with those 4 words and somewhat use them to come up
with a serial.
The Linux kernel serial ATAG (shown in cpuinfo) is only 2 32bit words,
so we will have to get rid of half of the (usable) SID.
AFAIK ATAG-s are pretty much dead when using a devicetree enabled platform,
how does this work in the devicetree world ?
The first half seems prefixed depending on the SoC platform, which
reduces the possible number of different combinations (but that's
probably not really a problem) and as Hans mentioned, it isn't unusual
to have a common part depending on the model. I suggest going with it.
Actually if we need to truncate I think it would be good to have as
much random bits in there as possible, we've a collection of SID-s here:
http://linux-sunxi.org/SID_Register_Guide
As you can see the last 32bit word is the most random one, for MAC
addresses we use the least significant byte of the first 32bit word
(which seems to be random in that table, but seems to be a fixed
value on later Axx SOCs) combined with the entire last 32 bit
word. So for the serial we could use the first and last 32 bit words,
this will give us the model prefix, instantly showing the soc model
in the serial + 32 unique bits per board.
Regards,
Hans
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