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SubjectRe: 2.6.29-rc libata sff 32bit PIO regression


Hugh Dickins wrote:
> On Mon, 26 Jan 2009, Alan Cox wrote:
>
>>> [PATCH] libata sff: 32bit PIO use 16bit on slop
>>>
>>> 871af1210f13966ab911ed2166e4ab2ce775b99d libata: Add 32bit PIO support
>>> causes errors on a four-year-old ata_piix Dell Precision 670. Using
>>> 16bit PIO instead of 32bit PIO on the odd 1, 2 or 3 chars fixes that.
>>>
>>> Signed-off-by: Hugh Dickins <hugh@veritas.com>
>>>
>> For the 3 bytes of slop it should use a single iowrite32 but otherwise
>> that seems ok. We do need to handle the FIFO setup on the AMD differently
>> if we do this ...
>>
>
> Sorry, I believe you were waiting on me for this, to accompany your
> AMD and VLB patches. I'm afraid I don't have any such AMD devices
> to test this along with yours, and the only non-0 slop that I've seen
> in testing has been 2 (about 25% of ops, so I removed the "unlikely").
> But this patch works as well for me as the patch I posted before
> (though much more verbose: please simplify if you see a better way).
>
>
> [PATCH] libata sff: 32bit PIO use 16bit on slop
>
> 871af1210f13966ab911ed2166e4ab2ce775b99d libata: Add 32bit PIO support
> causes errors on a four-year-old ata_piix Dell Precision 670. Using
> 16bit PIO instead of 32bit PIO on the odd 1 or 2 chars fixes that,
> but Alan Cox indicates that we should still use 32bit for 3 chars.
>
> Signed-off-by: Hugh Dickins <hugh@veritas.com>
> ---
>
> drivers/ata/libata-sff.c | 33 ++++++++++++++++++++++++---------
> 1 file changed, 24 insertions(+), 9 deletions(-)
>
> --- 2.6.29-rc3/drivers/ata/libata-sff.c 2009-01-29 12:33:28.000000000 +0000
> +++ linux/drivers/ata/libata-sff.c 2009-02-01 20:21:13.000000000 +0000
> @@ -773,18 +773,33 @@ unsigned int ata_sff_data_xfer32(struct
> else
> iowrite32_rep(data_addr, buf, words);
>
> - if (unlikely(slop)) {
> - __le32 pad;
> - if (rw == READ) {
> - pad = cpu_to_le32(ioread32(ap->ioaddr.data_addr));
> - memcpy(buf + buflen - slop, &pad, slop);
> + if (slop) {
> + unsigned char *trailing_buf = buf + buflen - slop;
>
> +
>
> + if (slop <= 2) {
> + __le16 slop_word;
> + if (rw == READ) {
> + slop_word = cpu_to_le16(ioread16(data_addr));
> + memcpy(trailing_buf, &slop_word, slop);
> + } else {
> + slop_word = 0;
> + memcpy(&slop_word, trailing_buf, slop);
> + iowrite16(le16_to_cpu(slop_word), data_addr);
> + }
> } else {
> - memcpy(&pad, buf + buflen - slop, slop);
> - iowrite32(le32_to_cpu(pad), ap->ioaddr.data_addr);
> + __le32 slop_word;
> + if (rw == READ) {
> + slop_word = cpu_to_le32(ioread32(data_addr));
> + memcpy(trailing_buf, &slop_word, slop);
> + } else {
> + slop_word = 0;
> + memcpy(&slop_word, trailing_buf, slop);
> + iowrite32(le32_to_cpu(slop_word), data_addr);
> + }
>

How about the following?

unsigned char *tail = buf + buflen - slop;
unsigned char pad[4];

if (rw == READ) {
if (slop <= 2)
ioread16_rep(data_addr, pad, 1);
else
ioread32_rep(data_addr, pad, 1);
memcpy(tail, pad, slop);
} else {
memcpy(pad, tail, slop);
memset(pad + slop, 0, 4 - slop);
if (slop <= 2)
iowrite16_rep(data_addr, pad, 1);
else
iowrite32_rep(data_addr, pad, 1);
}
> }
> - return words << 2;
> +
> + return buflen + (buflen & 1);
>

return (buflen + 1) & ~1;

Well, I guess I could just have posted my own patch... :-)

MBR, Sergei




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