On 10/28/22 17:14, John Garry wrote: > On 27/10/2022 23:35, Damien Le Moal wrote: >>> At what stage do you want to send these commands? The tags for the shost >>> are not setup until scsi_add_host() -> scsi_mq_setup_tags() is called, >>> so can't expect blk-mq to manage reserved tags before then. >>> >>> If you are required to send commands prior to scsi_add_host(), then I >>> suppose the low-level driver still needs to manage tags until the shost >>> is ready. I guess that some very simple scheme can be used, like always >>> use tag 0, since most probe is done serially per-host. But that's not a >>> case which I have had to deal with yet. >> In libata case, ata_dev_configure() will cause a lot of >> ata_exec_internal_sg() calls for IDENTIFY and various READ LOG commands. >> That is all done with non-ncq commands, which means that we do not require >> a hw tag. But given that you are changing ata_exec_internal_sg() to call >> alloc_request + blk_execute_rq_nowait(), how would these work without a >> tag, at least a soft one ? Or we would need to keep the current code to >> use ata_qc_issue() directly for probe time ? That will look very ugly... >> > > I am not sure if there is really a problem. So libata/libsas allocs the > shost quite early, and that is before we try using > ata_exec_internal_sg(). Also note that I added patch "ata: libata-scsi: > Allocate sdev early in port probe" so that we have ata_device.sdev ready > before issuing ata_exec_internal_sg() (sorry if I'm stating the obvious). > > I think Hannes' issue is that some SCSI HBA driver needs to send > "internal" commands to probe the HW for info, and this would be before > shost is ready. He can tell us more. OK. Understood. > > Thanks, > John -- Damien Le Moal Western Digital Research
