Located problem in pcn driver...

[John Gordon <john_94501%yahoo.com@localhost>]

Hello,

Well, after much hunting and a lot of debug code I have tracked down why my NS
1000 was unable to send anything over the network, despite being able to
receive packets correctly. Problem is I am not certain of how to solve it
correctly...

The problem is simple: the address of the data that is being inserted into the
transmit descriptor is not a PCI address, but a CPU address. On the NS 1000, as
with many PPC systems, the main memory is in the 0 -> 2GB portion of the CPU's
address space, but from the PCI side of the host bridge it is in in the 2GB ->
4GB range.

Now, the code in the pcn_start() routine is as follows:

if (sc->sc_swstyle == LE_B20_SSTYLE_PCNETPCI3) {
    for (nexttx = sc->sc_txnext, seg = 0;
        seg < dmamap->dm_nsegs;
        seg++, nexttx = PCN_NEXTTX(nexttx)) {
        /*
         * If this is the first descriptor we're
         * enqueueing, don't set the OWN bit just
         * yet.  That could cause a race condition.
         * We'll do it below.
         */
        sc->sc_txdescs[nexttx].tmd0 = 0;
        sc->sc_txdescs[nexttx].tmd2 =
            htole32(dmamap->dm_segs[seg].ds_addr);
        sc->sc_txdescs[nexttx].tmd1 =
            htole32(LE_T1_ONES |
                (nexttx == sc->sc_txnext ? 0 : LE_T1_OWN) |
                (LE_BCNT(dmamap->dm_segs[seg].ds_len) &
                 LE_T1_BCNT_MASK));
        lasttx = nexttx;
    }
}

The line in the middle of that loop that sets tmd2 is correctly handling the
translation to PCI's little endian, but it is not dealing with the difference
between the CPU's view of the address space, and the PCI bus' view of the
address space.

So, how do I fix this? Is the problem in this piece of code, or should the
ds_addr value already have been translated to a PCI-view address? Obviously,
for my testing it is simple to just set the top bit on the address, but how do
I do this correctly, and where (in the driver here, or in the DMA code that
sets up the ds_addr value in the first place)?

Suggestions welcomed...

Thanks,
John...

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