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    Subject[PATCH] libata: limit post SRST nsect/lbal wait to ~100ms
    After SRST, libata used to wait for nsect/lbal to be set to 1/1 for
    the slave device. However, some ATAPI devices don't set nsect/lbal
    after SRST and the wait itself isn't too useful as we're gonna wait
    for !BSY right after that anyway.

    Before reset-seq update, nsect/lbal wait failure used to be ignored
    and caused 30sec delay during detection. After reset-seq, all
    timeouts are considered error conditions making libata fail to detect
    such ATAPI devices.

    This patch limits nsect/lbal wait to around 100ms. This should give
    acceptable behavior to such ATAPI devices while not disturbing the
    heavily used code path too much.

    Signed-off-by: Tejun Heo <htejun@gmail.com>
    ---
    Okay, here it is. Sorry for the delay.

    drivers/ata/libata-core.c | 32 +++++++++++++++++++-------------
    1 file changed, 19 insertions(+), 13 deletions(-)

    diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
    index 4733f00..02a44ff 100644
    --- a/drivers/ata/libata-core.c
    +++ b/drivers/ata/libata-core.c
    @@ -3059,22 +3059,28 @@ static int ata_bus_post_reset(struct ata_port *ap, unsigned int devmask,
    }
    }

    - /* if device 1 was found in ata_devchk, wait for
    - * register access, then wait for BSY to clear
    + /* if device 1 was found in ata_devchk, wait for register
    + * access briefly, then wait for BSY to clear.
    */
    - while (dev1) {
    - u8 nsect, lbal;
    + if (dev1) {
    + int i;

    ap->ops->dev_select(ap, 1);
    - nsect = ioread8(ioaddr->nsect_addr);
    - lbal = ioread8(ioaddr->lbal_addr);
    - if ((nsect == 1) && (lbal == 1))
    - break;
    - if (time_after(jiffies, deadline))
    - return -EBUSY;
    - msleep(50); /* give drive a breather */
    - }
    - if (dev1) {
    +
    + /* Wait for register access. Some ATAPI devices fail
    + * to set nsect/lbal after reset, so don't waste too
    + * much time on it. We're gonna wait for !BSY anyway.
    + */
    + for (i = 0; i < 2; i++) {
    + u8 nsect, lbal;
    +
    + nsect = ioread8(ioaddr->nsect_addr);
    + lbal = ioread8(ioaddr->lbal_addr);
    + if ((nsect == 1) && (lbal == 1))
    + break;
    + msleep(50); /* give drive a breather */
    + }
    +
    rc = ata_wait_ready(ap, deadline);
    if (rc) {
    if (rc != -ENODEV)
    -
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