linux-kernel - Re: [PATCH v5 3/7] scsi: ufs: Fix up auto hibern8 enablement

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Date:   Fri, 15 Nov 2019 15:18:31 +0800
From:   Stanley Chu <stanley.chu@...iatek.com>
To:     Can Guo <cang@...eaurora.org>
CC:     <asutoshd@...eaurora.org>, <nguyenb@...eaurora.org>,
        <rnayak@...eaurora.org>, <linux-scsi@...r.kernel.org>,
        <kernel-team@...roid.com>, <saravanak@...gle.com>,
        <salyzyn@...gle.com>, Alim Akhtar <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....com>,
        Pedro Sousa <pedrom.sousa@...opsys.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Bean Huo <beanhuo@...ron.com>,
        Tomas Winkler <tomas.winkler@...el.com>,
        Venkat Gopalakrishnan <venkatg@...eaurora.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 3/7] scsi: ufs: Fix up auto hibern8 enablement

Hi Can,

On Fri, 2019-11-15 at 15:03 +0800, Can Guo wrote:
> On 2019-11-15 14:35, Stanley Chu wrote:
> > Hi Can,
> > 
> > On Thu, 2019-11-14 at 22:09 -0800, Can Guo wrote:
> >> +	if (hba->ahit != ahit)
> >> +		hba->ahit = ahit;
> >>  	spin_unlock_irqrestore(hba->host->host_lock, flags);
> >> +	if (!pm_runtime_suspended(hba->dev)) {
> > 
> > Always do pm_runtime_get_sync() here could avoid possible racing?
> > 
> > And thus AH8 could be enabled regardless of runtime status.
> > 
> >> +		pm_runtime_get_sync(hba->dev);
> >> +		ufshcd_hold(hba, false);
> >> +		ufshcd_auto_hibern8_enable(hba);
> >> +		ufshcd_release(hba);
> >> +		pm_runtime_put(hba->dev);
> >> +	}
> >>  }
> > 
> > Thanks,
> > Stanley
> 
> Hi Stanley,
> 
> if !pm_runtime_suspended() is true, hba->dev's runtime status, other 
> than RPM_ACTIVE,
> may be RPM_SUSPENDING or RPM_RESUMING. So, here for safty, do 
> pm_runtime_get_sync() once
> before access registers, in case we hit corner cases in which powers 
> and/or clocks are OFF.
> 

Thanks for explanation.

I fully understand the intention of this patch.

Just wonder if "if (!pm_runtime_suspended(hba->dev))" could be removed
and then always do pm_runtime_get_sync() here.

This could avoid possible racing and enable AH8 regardless of current
runtime status.

> Thanks,
> Can Guo.

Thanks,
Stanley