linux-kernel - Re: [PATCH v3 03/17] ufs: core: Introduce Multi-circular queue capability

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Message-ID: <20221028165116.GC9077@asutoshd-linux1.qualcomm.com>
Date:   Fri, 28 Oct 2022 09:51:16 -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>,
        "open list" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 03/17] ufs: core: Introduce Multi-circular queue
 capability

On Thu, Oct 27 2022 at 14:10 -0700, Bart Van Assche wrote:
>On 10/20/22 11:03, Asutosh Das wrote:
>>+
>>+	/*
>>+	 * This capability allows the host controller driver to turn on/off
>>+	 * MCQ mode. MCQ mode may be used to increase performance.
>>+	 */
>>+	UFSHCD_CAP_MCQ_EN				= 1 << 12,
>>  };
>
>I prefer that the above flag would only be introduced after a need 
>appears to disable MCQ, e.g. discovery of a host controller that is 
>too broken to enable MCQ.
>
I think this flag is useful during chip bring-ups &/or debugs.
Considering that this is a fairly new hardware block even though the HC supports
MCQ there could be times to keep it disabled.

>Since UFSHCI 4.0 controllers must support UFSHCI 3.0, shouldn't users 
>have a way to disable MCQ, e.g. via a kernel module parameter?
>
I can add a kernel module parameter to disable MCQ.
I think adding it to host driver (e.g. ufs-qcom) would be good.
Please let me know if you have a better place in mind.

>Thanks,
>
>Bart.