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    Subject[PATCH 5.10 005/530] Revert "USB: cdc-acm: fix rounding error in TIOCSSERIAL"
    Date
    From: Johan Hovold <johan@kernel.org>

    commit 729f7955cb987c5b7d7e54c87c5ad71c789934f7 upstream.

    This reverts commit b401f8c4f492cbf74f3f59c9141e5be3071071bb.

    The offending commit claimed that trying to set the values reported back
    by TIOCGSERIAL as a regular user could result in an -EPERM error when HZ
    is 250, but that was never the case.

    With HZ=250, the default 0.5 second value of close_delay is converted to
    125 jiffies when set and is converted back to 50 centiseconds by
    TIOCGSERIAL as expected (not 12 cs as was claimed, even if that was the
    case before an earlier fix).

    Comparing the internal current and new jiffies values is just fine to
    determine if the value is about to change so drop the bogus workaround
    (which was also backported to stable).

    For completeness: With different default values for these parameters or
    with a HZ value not divisible by two, the lack of rounding when setting
    the default values in tty_port_init() could result in an -EPERM being
    returned, but this is hardly something we need to worry about.

    Cc: Anthony Mallet <anthony.mallet@laas.fr>
    Cc: stable@vger.kernel.org
    Acked-by: Oliver Neukum <oneukum@suse.com>
    Signed-off-by: Johan Hovold <johan@kernel.org>
    Link: https://lore.kernel.org/r/20210408131602.27956-2-johan@kernel.org
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/usb/class/cdc-acm.c | 11 ++---------
    1 file changed, 2 insertions(+), 9 deletions(-)

    --- a/drivers/usb/class/cdc-acm.c
    +++ b/drivers/usb/class/cdc-acm.c
    @@ -942,7 +942,6 @@ static int set_serial_info(struct tty_st
    {
    struct acm *acm = tty->driver_data;
    unsigned int closing_wait, close_delay;
    - unsigned int old_closing_wait, old_close_delay;
    int retval = 0;

    close_delay = msecs_to_jiffies(ss->close_delay * 10);
    @@ -950,17 +949,11 @@ static int set_serial_info(struct tty_st
    ASYNC_CLOSING_WAIT_NONE :
    msecs_to_jiffies(ss->closing_wait * 10);

    - /* we must redo the rounding here, so that the values match */
    - old_close_delay = jiffies_to_msecs(acm->port.close_delay) / 10;
    - old_closing_wait = acm->port.closing_wait == ASYNC_CLOSING_WAIT_NONE ?
    - ASYNC_CLOSING_WAIT_NONE :
    - jiffies_to_msecs(acm->port.closing_wait) / 10;
    -
    mutex_lock(&acm->port.mutex);

    if (!capable(CAP_SYS_ADMIN)) {
    - if ((ss->close_delay != old_close_delay) ||
    - (ss->closing_wait != old_closing_wait))
    + if ((close_delay != acm->port.close_delay) ||
    + (closing_wait != acm->port.closing_wait))
    retval = -EPERM;
    else
    retval = -EOPNOTSUPP;

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