libata-eh: clear UNIT ATTENTION after reset
Resets make ATAPI devices raise UNIT ATTENTION which fails the next command. As resets can happen asynchronously for unrelated reasons, this sometimes disrupts innocent users. For example, reading DVD fails after the system wakes up from suspend or the other device sharing the channel went through bus error. Clearing UA has some problems as it might clear UA which the userland needs to know about. However, UA after resets can only be about the reset itself and benefits of clearing it overweights cons. Missing UA can only delay failure to one of the following commands anyway. For example, timeout while burning is in progress will trigger reset and reset the device state and probably corrupt the burning run. Although the userland application won't get the UA, its pending writes will fail. Signed-off-by: NTejun Heo <tj@kernel.org> Signed-off-by: NJeff Garzik <jgarzik@redhat.com>
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