- /*
- * The original PCI0646 didn't have the primary channel enable bit,
- * it appeared starting with PCI0646U (i.e. revision ID 3).
- */
- if (idx == 1 && dev->revision < 3)
- d.enablebits[0].reg = 0;
+ if (idx == 1) {
+ /*
+ * UltraDMA only supported on PCI646U and PCI646U2, which
+ * correspond to revisions 0x03, 0x05 and 0x07 respectively.
+ * Actually, although the CMD tech support people won't
+ * tell me the details, the 0x03 revision cannot support
+ * UDMA correctly without hardware modifications, and even
+ * then it only works with Quantum disks due to some
+ * hold time assumptions in the 646U part which are fixed
+ * in the 646U2.
+ *
+ * So we only do UltraDMA on revision 0x05 and 0x07 chipsets.
+ */
+ if (dev->revision < 5) {
+ d.udma_mask = 0x00;
+ /*
+ * The original PCI0646 didn't have the primary
+ * channel enable bit, it appeared starting with
+ * PCI0646U (i.e. revision ID 3).
+ */
+ if (dev->revision < 3) {
+ d.enablebits[0].reg = 0;
+ if (dev->revision == 1)
+ d.dma_ops = &cmd646_rev1_dma_ops;
+ else
+ d.dma_ops = &cmd64x_dma_ops;
+ }
+ }
+ }