First cut at the problem. Given the lack of certainty about worst case
buffer size (1 page I suspect) this uses kmalloc. We could hang a buffer
off the device (or I think in fact the port as we never do overlapped PIO)
diff -u --new-file --recursive --exclude-from /usr/src/exclude linux.vanilla-2.6.25-rc2-mm1/drivers/ata/libata-core.c linux-2.6.25-rc2-mm1/drivers/ata/libata-core.c
--- linux.vanilla-2.6.25-rc2-mm1/drivers/ata/libata-core.c 2008-02-19 11:03:26.000000000 +0000
+++ linux-2.6.25-rc2-mm1/drivers/ata/libata-core.c 2008-02-27 17:17:14.000000000 +0000
@@ -5052,6 +5052,60 @@
/**
+ * ata_bounce_pio_xfer - Transfer a block by PIO from high
+ * @dev: target device
+ * @page: highmem page
+ * @offset: offset in page
+ * @count: bytes to transfer
+ * @do_write: writing if set, reading if not
+ *
+ * Transfer a page of high memory via PIO. Whenever possible use a bounce
+ * buffer to avoid transfers occuring with local IRQ disable
+ */
+
+static void ata_bounce_pio_xfer(struct ata_device *dev, struct page *page,
+ unsigned int offset, int count, int do_write)
+{
+ struct ata_port *ap = dev->link->ap;
+ unsigned long flags;
+ unsigned char *zebedee;
+ unsigned char *buf;
+
+ BUG_ON(offset + count > PAGE_SIZE);
+
+ zebedee = kmalloc(count, GFP_ATOMIC);
+ if (likely(zebedee)) {
+ if (do_write) {
+ local_irq_save(flags);
+ buf = kmap_atomic(page, KM_IRQ0);
+ memcpy(zebedee, buf + offset, count);
+ kunmap_atomic(buf, KM_IRQ0);
+ local_irq_restore(flags);
+ }
+ /* do the actual data transfer */
+ ap->ops->data_xfer(dev, zebedee, count, do_write);
+ if (!do_write) {
+ /* Read so bounce data upwards */
+ local_irq_save(flags);
+ buf = kmap_atomic(page, KM_IRQ0);
+ memcpy(buf + offset, zebedee, count);
+ kunmap_atomic(buf, KM_IRQ0);
+ local_irq_restore(flags);
+ }
+ kfree(zebedee);
+ } else {
+ /* Only used when we are out of buffer memory
+ as a last last resort */
+ local_irq_save(flags);
+ buf = kmap_atomic(page, KM_IRQ0);
+ /* do the actual data transfer */
+ ap->ops->data_xfer(dev, buf + offset, count, do_write);
+ kunmap_atomic(buf, KM_IRQ0);
+ local_irq_restore(flags);
+ }
+}
+
+/**
* ata_pio_sector - Transfer a sector of data.
* @qc: Command on going
*
@@ -5081,21 +5135,13 @@
DPRINTK("data %s\n", qc->tf.flags & ATA_TFLAG_WRITE ? "write" : "read");
- if (PageHighMem(page)) {
- unsigned long flags;
-
- /* FIXME: use a bounce buffer */
- local_irq_save(flags);
- buf = kmap_atomic(page, KM_IRQ0);
-
- /* do the actual data transfer */
- ap->ops->data_xfer(qc->dev, buf + offset, qc->sect_size, do_write);
-
- kunmap_atomic(buf, KM_IRQ0);
- local_irq_restore(flags);
+ if (PageHighMem(page) || 1 /* TEST FIXME */) {
+ ata_bounce_pio_xfer(qc->dev, page, offset, qc->sect_size,
+ do_write);
} else {
buf = page_address(page);
- ap->ops->data_xfer(qc->dev, buf + offset, qc->sect_size, do_write);
+ ap->ops->data_xfer(qc->dev, buf + offset,
+ qc->sect_size, do_write);
}
qc->curbytes += qc->sect_size;
@@ -5242,19 +5288,9 @@
DPRINTK("data %s\n", qc->tf.flags & ATA_TFLAG_WRITE ? "write" : "read");
- if (PageHighMem(page)) {
- unsigned long flags;
-
- /* FIXME: use bounce buffer */
- local_irq_save(flags);
- buf = kmap_atomic(page, KM_IRQ0);
-
- /* do the actual data transfer */
- ap->ops->data_xfer(qc->dev, buf + offset, count, do_write);
-
- kunmap_atomic(buf, KM_IRQ0);
- local_irq_restore(flags);
- } else {
+ if (PageHighMem(page))
+ ata_bounce_pio_xfer(qc->dev, page, offset, count, do_write);
+ else {
buf = page_address(page);
ap->ops->data_xfer(qc->dev, buf + offset, count, do_write);
}
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