linux-kernel - Re: [PATCH v3 07/17] ufs: core: mcq: Calculate queue depth

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Date:   Mon, 31 Oct 2022 12:24:35 -0700
From:   Asutosh Das <quic_asutoshd@...cinc.com>
To:     Bart Van Assche <bvanassche@....org>
CC:     <quic_cang@...cinc.com>, <martin.petersen@...cle.com>,
        <linux-scsi@...r.kernel.org>, <quic_nguyenb@...cinc.com>,
        <quic_xiaosenh@...cinc.com>, <stanley.chu@...iatek.com>,
        <eddie.huang@...iatek.com>, <daejun7.park@...sung.com>,
        <avri.altman@....com>, <mani@...nel.org>, <beanhuo@...ron.com>,
        <quic_richardp@...cinc.com>, <linux-arm-msm@...r.kernel.org>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Andy Gross" <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Jinyoung Choi <j-young.choi@...sung.com>,
        Kiwoong Kim <kwmad.kim@...sung.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 07/17] ufs: core: mcq: Calculate queue depth

On Thu, Oct 27 2022 at 14:52 -0700, Bart Van Assche wrote:
>On 10/20/22 11:03, Asutosh Das wrote:
>>+u32 ufshcd_mcq_decide_queue_depth(struct ufs_hba *hba)
>>+{
>>+	u32 qd, val;
>>+	int mac;
>>+
>>+	mac = ufshcd_mcq_vops_get_hba_mac(hba);
>>+	if (mac < 0) {
>>+		val = ufshcd_readl(hba, REG_UFS_MCQ_CFG);
>>+		mac = FIELD_GET(MCQ_CFG_MAC_MASK, val);
>>+	}
>
>According to the UFSHCI 4.0 specification the MAC value is set by the 
>host. Can the above code read the MAC value from the host controller 
>before it has been set by the host? If so, how about leaving out the 
>code that reads the MAC value from the controller and making it 
>mandatory to implement the new get_hba_mac vop?
>
The reason it is not mandatory to define get_hba_mac vop is UFSHCI 4.0
specification mentions that the default value of MAC is 32. So even if a vendor
HC doesn't override the MAC, it'd be 32.
Hence, the current code first checks for an override, and if there's none uses
the default value defined in the HC.

-asd