Re: [PATCH v3 18/21] nvme: Update CCR completion wait timeout to consider CQT

[Mohamed Khalfella <mkhalfella@purestorage.com>]

On Tue 2026-02-17 08:09:33 +0100, Hannes Reinecke wrote:
> On 2/16/26 19:45, Mohamed Khalfella wrote:
> > On Mon 2026-02-16 13:54:18 +0100, Hannes Reinecke wrote:
> >> On 2/14/26 05:25, Mohamed Khalfella wrote:
> >>> TP8028 Rapid Path Failure Recovery does not define how much time the
> >>> host should wait for CCR operation to complete. It is reasonable to
> >>> assume that CCR operation can take up to ctrl->cqt. Update wait time for
> >>> CCR operation to be max(ctrl->cqt, ctrl->kato).
> >>>
> >>> Signed-off-by: Mohamed Khalfella <mkhalfella@purestorage.com>
> >>> ---
> >>>    drivers/nvme/host/core.c | 2 +-
> >>>    1 file changed, 1 insertion(+), 1 deletion(-)
> >>>
> >>> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> >>> index 0680d05900c1..ff479c0263ab 100644
> >>> --- a/drivers/nvme/host/core.c
> >>> +++ b/drivers/nvme/host/core.c
> >>> @@ -631,7 +631,7 @@ static int nvme_issue_wait_ccr(struct nvme_ctrl *sctrl, struct nvme_ctrl *ictrl)
> >>>    	if (result & 0x01) /* Immediate Reset Successful */
> >>>    		goto out;
> >>>    
> >>> -	tmo = secs_to_jiffies(ictrl->kato);
> >>> +	tmo = msecs_to_jiffies(max(ictrl->cqt, ictrl->kato * 1000));
> >>>    	if (!wait_for_completion_timeout(&ccr.complete, tmo)) {
> >>>    		ret = -ETIMEDOUT;
> >>>    		goto out;
> >>
> >> That is not my understanding. I was under the impression that CQT is the
> >> _additional_ time a controller requires to clear out outstanding
> >> commands once it detected a loss of communication (ie _after_ KATO).
> >> Which would mean we have to wait for up to
> >> (ctrl->kato * 1000) + ctrl->cqt.
> > 
> > At this point the source controller knows about communication loss. We
> > do not need kato wait. In theory we should just wait for CQT.
> > max(cqt, kato) is a conservative guess I made.
> > 
> Not quite. The source controller (on the host!) knows about the
> communication loss. But the target might not, as the keep-alive
> command might have arrived at the target _just_ before KATO
> triggered on the host. So the target is still good, and will
> be waiting for _another_ KATO interval before declaring
> a loss of communication.
> And only then will the CQT period start at the target.
> 
> Randy, please correct me if I'm wrong ...
> 

wait_for_completion_timeout(&ccr.complete, tmo)) waits for CCR operation
to complete. The wait starts after CCR command completed successfully.
IOW, it starts after the host received a CQE from source controller on
the target telling us all is good. If the source controller on the target
already know about loss of communication then there is no need to wait
for KATO. We just need to wait for CCR operation to finish because we
know it has been started successfully.

The specs does not tell us how much time to wait for CCR operation to
complete. max(cqt, kato) is an estimate I think reasonable to make.