libata: Improve ATA queued command allocation
Improve ATA queued command allocation as follows:
- For attaining a qc tag for a SAS host we need to allocate a bit in
ata_port.sas_tag_allocated bitmap.
However we already have a unique tag per device in range
[0, ATA_MAX_QUEUE -1] in the scsi cmnd budget token, so just use that
instead.
- It is a bit pointless to have ata_qc_new_init() in libata-core.c since it
pokes scsi internals, so inline it in ata_scsi_qc_new() (in
libata-scsi.c). Also update Doc accordingly.
- Use standard SCSI helpers set_host_byte() and set_status_byte() in
ata_scsi_qc_new().
Christoph Hellwig originally contributed the change to inline
ata_qc_new_init().
Signed-off-by: John Garry <john.garry@huawei.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>