Re: [PATCH RFC v2 03/18] scsi: core: Implement reserved command handling

[Christoph Hellwig]

On Mon, Jun 20, 2022 at 08:24:24AM +0200, Hannes Reinecke wrote:
> So my idea for SATA is simply _not_ to use reserved tags.
> Any TMF functions (or the equivalent thereof) should always be sent as 
> non-NCQ commands. And when doing so we're back to QD=1 on SATA anyway, so 
> there _must_ be tags available. Consequently the main reason for having 
> reserved tags (namely to guarantee that tags are available for TMF) doesn't 
> apply here.

At least in the non-elevator case (which includes all passthrough I/O)
request have tags assigned as soon as they are allocated.  So, we
absolutely can have all tags allocated and then need to do a TMF.