[openib-general] Re: [PATCH] mthca: fix max wr for arbel

[Roland Dreier]

    Michael> Unlike tavor, max QP/SRQ size is a power of 2 for arbel
    Michael> mode, despite what the documentation (of the query dev
    Michael> lim command) says.  Without this patch, on Arbel, we can
    Michael> start with a qp of a legal size and get above the device
    Michael> limit after rounding to the next power of two.

This looks fine but I'm a little confused by the explanation.  If the
firmware reports a limit of say 14, then the current code will turn
that into a limit of 16383 work queue entries, but the actual hardware
limit is 16384 entries.

So the code in mthca_set_qp_size() will reject attempts to create a QP
with more than 16383 entries.  If someone tries to create a QP with
more than 8192 entries, the size will get rounded up to 16384, which
will still work with the hardware.

Or did you just mean that sometimes a QP will be created with a size
bigger than the limit reported by the driver?  I agree that's not
ideal but it doesn't seem to be a major problem.

 - R.