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

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Message-ID: <87a78633-5c9e-49c2-4e8a-8b1c6b21f2f0@acm.org>
Date:   Mon, 31 Oct 2022 12:42:15 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Asutosh Das <quic_asutoshd@...cinc.com>
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 10/31/22 12:24, Asutosh Das wrote:
> 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.

Hi Asutosh,

Please ignore the value reported by the controller in the MAC field of 
the MCQConfig register and overwrite the MAC field without reading it 
first. It doesn't seem useful to me to read this field. I think the host 
should decide about the queue depth no matter what the current value of 
the MAC field is.

Thanks,

Bart.