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

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Message-ID: <6b298597-f3b3-e4a1-c59a-f704ad4c06e5@acm.org>
Date:   Tue, 15 Feb 2022 09:15:43 -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 2/14/22 22:03, Kiwoong Kim wrote:
> The benefit that I think is not blocking dev cmd during submitting a scsi cmd.

Hi Kiwoong,

Both ufshcd_exec_dev_cmd() and previous versions of 
ufshcd_queuecommand() obtain a reader lock on the clock scaling lock so 
concurrent submission of both command types is allowed. I'm not aware of 
any version of the UFS driver that serializes device commands against 
SCSI commands.

Additionally, please take a look at commit 8d077ede48c1 ("scsi: ufs: 
Optimize the command queueing code"). That patch removes the clock 
scaling lock from ufshcd_queuecommand().

Thanks,

Bart.