it uses the following test to determine whether the timeout has
expired:

        if (jiffies - dma_start > PCNET_RDC_TIMEOUT) {

Unfortunately, PCNET_RDC_TIMEOUT is defined to be "0x02", so the
length of the timeout is only two jiffy ticks, rather than being
the expected 20ms.  This patch fixes this.

Also, the above (and one other place) should be converted to
time_after().