libata-sff: fix 32-bit PIO ATAPI regression

Commit 871af1210f13966ab911ed2166e4ab2ce775b99d (libata: Add 32bit
PIO support) has caused all kinds of errors on the ATAPI devices, so
it has been empirically proven that one shouldn't try to read/write
an extra data word when a device is not expecting it already. "Don't
do it then"; however, still use a chance to do 32-bit read/write one
last time when there are exactly 3 trailing bytes.

Oh, and stop pointlessly swapping the bytes to and fro on big-endian
machines by using io*_rep() accessors which shouldn't byte-swap.

This patch should fix the kernel.org bug #12609.

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

1 files changed, 21 insertions, 7 deletions

diff --git a/drivers/ata/libata-sff.c b/drivers/ata/libata-sff.c
index 0b299b0f8172..714cb046b594 100644
--- a/drivers/ata/libata-sff.c
+++ b/drivers/ata/libata-sff.c
@@ -773,18 +773,32 @@ unsigned int ata_sff_data_xfer32(struct ata_device *dev, unsigned char *buf,
         else
                 iowrite32_rep(data_addr, buf, words);
 
+        /* Transfer trailing bytes, if any */
         if (unlikely(slop)) {
-                __le32 pad;
+                unsigned char pad[4];
+
+                /* Point buf to the tail of buffer */
+                buf += buflen - slop;
+
+                /*
+                 * Use io*_rep() accessors here as well to avoid pointlessly
+                 * swapping bytes to and fro on the big endian machines...
+                 */
                 if (rw == READ) {
-                        pad = cpu_to_le32(ioread32(ap->ioaddr.data_addr));
-                        memcpy(buf + buflen - slop, &pad, slop);
+                        if (slop < 3)
+                                ioread16_rep(data_addr, pad, 1);
+                        else
+                                ioread32_rep(data_addr, pad, 1);
+                        memcpy(buf, pad, slop);
                 } else {
-                        memcpy(&pad, buf + buflen - slop, slop);
-                        iowrite32(le32_to_cpu(pad), ap->ioaddr.data_addr);
+                        memcpy(pad, buf, slop);
+                        if (slop < 3)
+                                iowrite16_rep(data_addr, pad, 1);
+                        else
+                                iowrite32_rep(data_addr, pad, 1);
                 }
-                words++;
         }
-        return words << 2;
+        return (buflen + 1) & ~1;
 }
 EXPORT_SYMBOL_GPL(ata_sff_data_xfer32);