linux-kernel - Re: [PATCH v4] scsi: ufs: core: Don't perform UFS clkscale if host asyn scan in progress

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Message-ID: <08dcffa6-6cf9-4c79-8aa9-a82bd42d3932@acm.org>
Date: Wed, 30 Jul 2025 08:50:32 -0700
From: Bart Van Assche <bvanassche@....org>
To: Peter Wang (王信友) <peter.wang@...iatek.com>,
 "beanhuo@...ron.com" <beanhuo@...ron.com>,
 "avri.altman@....com" <avri.altman@....com>,
 "neil.armstrong@...aro.org" <neil.armstrong@...aro.org>,
 "quic_cang@...cinc.com" <quic_cang@...cinc.com>,
 "quic_nitirawa@...cinc.com" <quic_nitirawa@...cinc.com>,
 "quic_nguyenb@...cinc.com" <quic_nguyenb@...cinc.com>,
 "quic_ziqichen@...cinc.com" <quic_ziqichen@...cinc.com>,
 "luca.weiss@...rphone.com" <luca.weiss@...rphone.com>,
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 "quic_rampraka@...cinc.com" <quic_rampraka@...cinc.com>,
 "junwoo80.lee@...sung.com" <junwoo80.lee@...sung.com>
Cc: "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
 Tze-nan Wu (吳澤南) <Tze-nan.Wu@...iatek.com>,
 "linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
 "manivannan.sadhasivam@...aro.org" <manivannan.sadhasivam@...aro.org>,
 "alim.akhtar@...sung.com" <alim.akhtar@...sung.com>,
 "James.Bottomley@...senPartnership.com"
 <James.Bottomley@...senPartnership.com>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] scsi: ufs: core: Don't perform UFS clkscale if host
 asyn scan in progress

On 7/30/25 5:55 AM, Peter Wang (王信友) wrote:
> Another idea is to only start ufshcd_devfreq_init
> when shost->async_scan = 0.

Hmm ... I don't think that this is a solution. There are multiple
ways for triggering a LUN scan and my understanding is that the
clock scaling code should be serialized against LUN scanning.

Here is an example of how LUN scanning can be triggered from user
space by writing into the 'scan' sysfs attribute, even if
shost->async_scan = 0:

echo "- - -" > /sys/class/scsi_host/host.../scan

Bart.