linux-kernel - Re: [PATCH v11 1/3] scsi: ufs: Protect some contexts from unexpected clock scaling

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Date:   Wed, 20 Jan 2021 21:14:32 +0800
From:   Stanley Chu <stanley.chu@...iatek.com>
To:     Can Guo <cang@...eaurora.org>
CC:     <asutoshd@...eaurora.org>, <nguyenb@...eaurora.org>,
        <hongwus@...eaurora.org>, <linux-scsi@...r.kernel.org>,
        <kernel-team@...roid.com>, Alim Akhtar <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Bean Huo <beanhuo@...ron.com>,
        "Satya Tangirala" <satyat@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v11 1/3] scsi: ufs: Protect some contexts from
 unexpected clock scaling

On Wed, 2021-01-20 at 02:04 -0800, Can Guo wrote:
> In contexts like suspend, shutdown and error handling, we need to suspend
> devfreq to make sure these contexts won't be disturbed by clock scaling.
> However, suspending devfreq is not enough since users can still trigger a
> clock scaling by manipulating the devfreq sysfs nodes like min/max_freq and
> governor even after devfreq is suspended. Moreover, mere suspending devfreq
> cannot synchroinze a clock scaling which has already been invoked through
> these sysfs nodes. Add one more flag in struct clk_scaling and wrap the
> entire func ufshcd_devfreq_scale() with the clk_scaling_lock, so that we
> can use this flag and clk_scaling_lock to control and synchronize clock
> scaling invoked through devfreq sysfs nodes.
> 
> Signed-off-by: Can Guo <cang@...eaurora.org>

Reviewed-by: Stanley Chu <stanley.chu@...iatek.com>