[I'm not subscribed, so please Cc: me directly.  Thanks.]

patch-2.4.19-rc3-ac3 has this stuff related to highmem support:

 /*
+ * mapping stuff, prepare for highmem...
+ * 
+ * temporarily mapping a (possible) highmem bio for PIO transfer
+ */
+#define ide_rq_offset(rq) \
+       (((rq)->hard_cur_sectors - (rq)->current_nr_sectors) << 9)
+
+extern inline void *ide_map_buffer(struct request *rq, unsigned long
*flags)
+{
+       return rq->buffer + ide_rq_offset(rq);
+}
+
+extern inline void ide_unmap_buffer(char *buffer, unsigned long *flags)
+{
+       do { } while (0);
+}

Red Hat's 2.4.18-5 kernel has these conflicting bits in
linux-2.4.17-blockhighmem.patch:

+
+/*
+ * temporarily mapping a (possible) highmem bio
+ */
+#define ide_rq_offset(rq) (((rq)->hard_cur_sectors - (rq)->current_nr_sectors) << 9)
+
+extern inline void *ide_map_buffer(struct request *rq, unsigned long
*flags)
+{
+       return bh_kmap_irq(rq->bh, flags) + ide_rq_offset(rq);
+}
+
+extern inline void ide_unmap_buffer(char *buffer, unsigned long *flags)
+{
+       bh_kunmap_irq(buffer, flags);
+}

Which one should I apply? I'm inclined to keep the Red Hat bits, since
the ac3 ide_unmap_buffer does nothing.

[For anyone wondering, I have a new Dell with an Intel 845G chipset for
which I would like DMA support, etc.  I'm attempting to merge
2.4.19-rc3-ac3 with Red Hat's patches.  If anyone has a simple patch for
82801DB IDE DMA support which applies to 2.4.18 I'd be much obliged.]

Thanks.

-- 
Charles R. Anderson <cra@wpi.edu> / http://angus.ind.wpi.edu/~cra/
PGP Key ID: 49BB5886
Fingerprint: EBA3 A106 7C93 FA07 8E15  3AC2 C367 A0F9 49BB 5886
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