On Tue, Mar 21, 2023 at 07:36:12AM -0700, Bart Van Assche wrote: > The UFSHCI specification is very clear about the requirement that UFS host > controllers must process SCSI commands in order if host software sets one > bit at a time in the UFSHCI 3.0 doorbell register: "For Task Management > Requests and Transfer Requests, software may issue multiple commands at a > time, and may issue new commands before previous commands have completed. > When software sets the corresponding doorbell register, the Task Management > Requests and Transfer Requests automatically get a time stamp with their > issue time. The commands within a command list (Task Management List or > Transfer Request List) shall be processed in > the order of their time stamps, starting from the oldest time stamp. In the > case multiple commands from the same list have the same time stamp, they > shall be processed in the order of their command list index, > starting from the lowest index." But we can't write Linux software just for UFS. We have no sensible ordering guarantee anywhere else. > Damien and Jens agree about introducing an additional hardware queue for > preserving the order of zoned writes as one can see here: > https://lore.kernel.org/linux-block/ed255a4a-a0da-a962-2da4-13321d0a75c5@xxxxxxxxx/ > > In our tests pipelining zoned writes (REQ_OP_WRITE) works fine as long as > the UFS error handler is not activated. After the UFS error handler has > been scheduled and before the SCSI host state is changed into > SHOST_RECOVERY, the UFS host controller driver responds with > SCSI_MLQUEUE_HOST_BUSY. I'm still working on a solution for the reordering > caused by this mechanism. We'll still need REQ_OP_ZONE_APPEND as the actual file system fast path interface. For a low-end device like UFS the sd.c emulation might be able to take advantage of the above separate queue as an implementation detail.
