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Message-ID: <3056c6d8-1e54-4954-9141-e0760a0d935a@acm.org>
Date:   Wed, 25 Oct 2023 11:10:59 -0700
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User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH v1 1/1] ufs: core: Add host quirk
 QUIRK_MCQ_EXPAND_QUEUE_SLOT
Content-Language: en-US
To:     Chun-Hung Wu <chun-hung.wu@mediatek.com>,
        Alim Akhtar <alim.akhtar@samsung.com>,
        Avri Altman <avri.altman@wdc.com>,
        "James E . J . Bottomley" <jejb@linux.ibm.com>,
        "Martin K . Petersen" <martin.petersen@oracle.com>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@collabora.com>,
        Can Guo <quic_cang@quicinc.com>,
        Manivannan Sadhasivam <mani@kernel.org>,
        Asutosh Das <quic_asutoshd@quicinc.com>,
        "Bao D . Nguyen" <quic_nguyenb@quicinc.com>,
        Yang Li <yang.lee@linux.alibaba.com>,
        Eric Biggers <ebiggers@google.com>,
        Keoseong Park <keosung.park@samsung.com>,
        Arthur Simchaev <Arthur.Simchaev@wdc.com>
Cc:     wsd_upstream@mediatek.com, casper.li@mediatek.com,
        peter.wang@mediatek.com, powen.kao@mediatek.com,
        alice.chao@mediatek.com, naomi.chu@mediatek.com,
        cc.chou@mediatek.com, chaotian.jing@mediatek.com,
        jiajie.hao@mediatek.com, tun-yu.yu@mediatek.com,
        lin.gui@mediatek.com, eddie.huang@mediatek.com,
        qilin.tan@mediatek.com, linux-scsi@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org, kernel-team@android.com
References: <20231025085656.10848-1-chun-hung.wu@mediatek.com>
 <20231025085656.10848-2-chun-hung.wu@mediatek.com>
From:   Bart Van Assche <bvanassche@acm.org>
In-Reply-To: <20231025085656.10848-2-chun-hung.wu@mediatek.com>
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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.