Re: [PATCH v1 1/1] ufs: core: Add host quirk QUIRK_MCQ_EXPAND_QUEUE_SLOT

[Chun-Hung Wu (巫駿宏)]

On Fri, 2023-10-27 at 13:55 -0700, Bart Van Assche wrote:
>  	 
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>  On 10/26/23 20:27, Chun-Hung Wu (巫駿宏) wrote:
> > From UFSHCI 4.0 spec "When the head and tail doorbells are equal,
> the
> > queue is empty. *Nothe that this definition means there will always
> be
> > one empty queue entry"
> > One of our platform does not keep one empty queue
> > entry for CQ full
> > case, that's  why we need this patch to fix this corner case.
> 
> The UFSHCI driver should make sure that there is always one empty
> queue
> entry. Does "platform" in the above text refer to the SoC that
> includes
> the UFSHCI controller?
Yes here "platform" indicates SoC that includes the UFSHCI controller.
> 
> What is totally unclear to me is why the following code depends on
> the
> UFSHCI controller type:
> 
> +if (ufshcd_is_mcq_expand_queue_slot(hba))
> +hwq->max_entries = hba->nutrs + 1;
> +else
> +hwq->max_entries = hba->nutrs;
> 
> Shouldn't hwq->max_entries = hba->nutrs + 1 be used for all UFSHCI
> 4.0
> controllers?
> 
> Thanks,
> 
> Bart.
> 
I think UFSHCI 4.0 spec "When the head and tail doorbells are equal,the
queue is empty. *Nothe that this definition means there will alwaysbe
one empty queue entry" means that "UFSHCI controller" should always
keep one empty queue entry.
One of our host does not follow the spec, therefore, this host will
treat CQ full(head = tail) as CQ empty (head = tail). That's why we
propose this quirk to expand one queue slot for hosts have such issue.
It will make CQ full(head != tail)[keep one empty queue entry] not
equal to CQ empty(head = tail).
hwq->max_entries will be used to set SQ&CQ size in SQ&CQ Configuration
Registers, we think it should only apply to specific hosts need this
quirk not all.

Thanks,
Chun-Hung