linux-kernel - Re: [PATCH v1 1/1] ufs: core: Add host quirk QUIRK_MCQ_EXPAND_QUEUE

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Date:   Wed, 25 Oct 2023 11:10:59 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Chun-Hung Wu <chun-hung.wu@...iatek.com>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....com>,
        "James E . J . Bottomley" <jejb@...ux.ibm.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Can Guo <quic_cang@...cinc.com>,
        Manivannan Sadhasivam <mani@...nel.org>,
        Asutosh Das <quic_asutoshd@...cinc.com>,
        "Bao D . Nguyen" <quic_nguyenb@...cinc.com>,
        Yang Li <yang.lee@...ux.alibaba.com>,
        Eric Biggers <ebiggers@...gle.com>,
        Keoseong Park <keosung.park@...sung.com>,
        Arthur Simchaev <Arthur.Simchaev@....com>
Cc:     wsd_upstream@...iatek.com, casper.li@...iatek.com,
        peter.wang@...iatek.com, powen.kao@...iatek.com,
        alice.chao@...iatek.com, naomi.chu@...iatek.com,
        cc.chou@...iatek.com, chaotian.jing@...iatek.com,
        jiajie.hao@...iatek.com, tun-yu.yu@...iatek.com,
        lin.gui@...iatek.com, eddie.huang@...iatek.com,
        qilin.tan@...iatek.com, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, kernel-team@...roid.com
Subject: Re: [PATCH v1 1/1] ufs: core: Add host quirk
 QUIRK_MCQ_EXPAND_QUEUE_SLOT

On 10/25/23 01:56, Chun-Hung Wu wrote:
> This quirk needs to be enabled if the host controller cannot 
> distinguish queue full or empty.

 From the UFSHCI 4.0 specification: "When the head and tail doorbells are
equal, the queue is empty. [ ... ] When the head and tail doorbells are
not equal, the queue contains queue entries."

How is it possible that a host controller cannot distinguish queue full
or queue empty? Which (head - tail) values cause trouble? More
information is needed.

Thanks,

Bart.