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

[Bart Van Assche <bvanassche@acm.org>]

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.