linux-kernel - Re: [PATCH v4 07/16] ufs: core: mcq: Calculate queue depth

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Date:   Wed, 9 Nov 2022 13:28:44 -0800
From:   Bart Van Assche <bvanassche@....org>
To:     Asutosh Das <quic_asutoshd@...cinc.com>, quic_cang@...cinc.com,
        martin.petersen@...cle.com, linux-scsi@...r.kernel.org
Cc:     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, 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 <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Jinyoung Choi <j-young.choi@...sung.com>,
        Arthur Simchaev <Arthur.Simchaev@....com>,
        Kiwoong Kim <kwmad.kim@...sung.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 07/16] ufs: core: mcq: Calculate queue depth

On 11/9/22 11:41, Asutosh Das wrote:
> +int ufshcd_mcq_decide_queue_depth(struct ufs_hba *hba)
> +{
> +	int mac;
> +
> +	/* Mandatory to implement get_hba_mac() */
> +	mac = ufshcd_mcq_vops_get_hba_mac(hba);
> +	if (mac < 0) {
> +		dev_err(hba->dev, "Failed to get mac, err=%d\n", mac);
> +		return mac;
> +	}
> +
> +	/*  MAC is a 0 based value. */
> +	mac += 1;

Please make ufshcd_mcq_vops_get_hba_mac() return a 1-based value. The 
0-based convention is useful for bit-constrained device registers but is 
confusing when not reading from a hardware register.

> +	/*
> +	 * max. value of bqueuedepth = 256, mac is host dependent.
> +	 * It is mandatory for UFS device to define bQueueDepth if
> +	 * shared queuing architecture is enabled.
> +	 */
> +	return min_t(int, mac, hba->dev_info.bqueuedepth);

According to the UFS specification bQueueDepth is zero if there is one 
queue per logical unit inside the device. Should a warning statement be 
added that reports a complaint if bQueueDepth == 0 since the above code 
does not support bQueueDepth == 0? I'm not sure whether any UFS devices 
exist that use per-LU queuing.

> +static int ufs_qcom_get_hba_mac(struct ufs_hba *hba)
> +{
> +	/* Default is 32, but Qualcomm HC supports upto 64 */

I think that "default is 32" should be left out since the code that 
reads the MAC register has been removed.

Additionally, please change "upto" into "up to".

Thanks,

Bart.