RE: [EXT] [PATCH RFC v2 4/5] ufs: Use blk_{get,put}_request() to allocate and free TMFs

["Bean Huo (beanhuo)" <beanhuo@micron.com>]

> On 11/5/19 5:50 AM, Bean Huo (beanhuo) wrote:
> >> -	wait_event(hba->tm_tag_wq, ufshcd_get_tm_free_slot(hba,
> >> &free_slot));
> >> +	req = blk_get_request(q, REQ_OP_DRV_OUT, BLK_MQ_REQ_RESERVED);
> >> +	req->end_io_data = &wait;
> >> +	free_slot = req->tag;
> >> +	WARN_ON_ONCE(free_slot < 0 || free_slot >= hba->nutmrs);
> >>   	ufshcd_hold(hba, false);
> >>
> > Understand now , you delete ufshcd_get_tm_free_slot(). Run a big circle to
> get a free_slot from reserved tags by calling blk_get_request().
> > But UFS data transfer queue depth is 32, not 32 + hba->nutmrs.  How to make
> sure we see the tag is consistent across block/scsi/ufs?
> 
> Hi Bean,
> 
> Please have a look at the blk_mq_get_tag() function in the block layer.
> The implementation of that function makes it clear that the tags with numbers
> [0 .. nr_reserved) are considered reserved tags and also that the tags with
> numbers [nr_reserved .. queue_depth) are considered regular tags. In other
> words, adding hba->nutmrs to can_queue does not increase the queue depth
> because the same number of tags are considered reserved tags.
> 
> Bart.

Hi, Bart
Yes, I saw that. And actually, task management requests and regular data transfer
Requests will be stored to different queues, and use different door-bell registers.
So as you said, to introduce a new tag set for TMFs is better.
Thanks,

//Bean