bug in moxa.c driver (+ patch, please apply)

[David Monniaux]

SYMPTOMS:
The current Moxa Intellio driver (moxa.c) panics when using > 1 board.

BACKGROUND:
The Moxa board needs a firmware download (see
http://www.moxa.com/drivers/C320T/Linux/v5.4/MXDRV.TGZ, command
moxaload -y) prior to usage.

Unfortunately, the current Linux kernel code fails during this download if
more than one board are installed.

EXPLANATION AND FIX:
The MoxaDriverPoll function does:
[...]
        for (card = 0; card < MAX_BOARDS; card++) {
                if ((ports = moxa_boards[card].numPorts) == 0)
                        continue;
                if (readb(moxaIntPend[card]) == 0xff) {
[...]

Unfortunately, with multiple boards, there exists a point where
MoxaDriverPoll() will be called when moxa_boards[card].numPorts != 0 but
moxaIntPend[card] is still NULL. Result: kernel panic.

Fix: use instead
                if ((ports = moxa_boards[card].numPorts) == 0
                    || moxaIntPend[card] == 0)
                        continue;

If someone who understands the code better than me proposes a better
patch, I'd be delighted. [For the little story, the above patch was
written after finding the bug in a remote location without internet access
using a serial console for getting the panic trace...]

David Monniaux            http://www.di.ens.fr/~monniaux
Laboratoire d'informatique de l'École Normale Supérieure,
Paris, France

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