linux-kernel - Re: [PATCH v1] scsi: ufs: remove clk_scaling

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Message-ID: <62a5170b-48c0-a372-5392-08f5112d7a06@acm.org>
Date:   Mon, 14 Feb 2022 11:29:08 -0800
From:   Bart Van Assche <bvanassche@....org>
To:     Kiwoong Kim <kwmad.kim@...sung.com>, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org, alim.akhtar@...sung.com,
        avri.altman@....com, jejb@...ux.ibm.com,
        martin.petersen@...cle.com, beanhuo@...ron.com,
        cang@...eaurora.org, adrian.hunter@...el.com, sc.suh@...sung.com,
        hy50.seo@...sung.com, sh425.lee@...sung.com,
        bhoon95.kim@...sung.com, vkumar.1997@...sung.com
Subject: Re: [PATCH v1] scsi: ufs: remove clk_scaling_lock when clkscaling
 isn't supported.

On 2/4/22 23:39, Kiwoong Kim wrote:
> clk_scaling_lock is to prevent from running clkscaling related operations
> with others which might be affected by the operations concurrently.
> I think it looks hardware specific.
> If the feature isn't supported, I think there is no reasonto prevent from
> running other functions, such as ufshcd_queuecommand and
> ufshcd_exec_dev_cmd, concurrently.
> 
> So I add a condition at some points protecting with clk_scaling_lock.
> 
> Signed-off-by: Kiwoong Kim <kwmad.kim@...sung.com>
> ---
>   drivers/scsi/ufs/ufshcd.c | 21 ++++++++++++++-------
>   1 file changed, 14 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> index 460d2b4..8471c90 100644
> --- a/drivers/scsi/ufs/ufshcd.c
> +++ b/drivers/scsi/ufs/ufshcd.c
> @@ -2980,7 +2980,8 @@ static int ufshcd_exec_dev_cmd(struct ufs_hba *hba,
>   	/* Protects use of hba->reserved_slot. */
>   	lockdep_assert_held(&hba->dev_cmd.lock);
>   
> -	down_read(&hba->clk_scaling_lock);
> +	if (ufshcd_is_clkscaling_supported(hba))
> +		down_read(&hba->clk_scaling_lock);
>   
>   	lrbp = &hba->lrb[tag];
>   	WARN_ON(lrbp->cmd);

I don't like this patch at all. This patch makes testing the UFS driver 
more complicated without having any clear benefit. Additionally, adding 
if-statements in front of locking makes static source code analysis 
harder and is an anti-pattern. Please don't do this.

Bart.