linux-kernel - Re: [PATCH v1 1/2] scsi: ufs: add required delay after gating reference clock

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Date:   Mon, 17 Feb 2020 21:22:49 +0800
From:   Can Guo <cang@...eaurora.org>
To:     Stanley Chu <stanley.chu@...iatek.com>
Cc:     linux-scsi@...r.kernel.org, martin.petersen@...cle.com,
        avri.altman@....com, alim.akhtar@...sung.com, jejb@...ux.ibm.com,
        beanhuo@...ron.com, asutoshd@...eaurora.org,
        matthias.bgg@...il.com, bvanassche@....org,
        linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kuohong.wang@...iatek.com, peter.wang@...iatek.com,
        chun-hung.wu@...iatek.com, andy.teng@...iatek.com
Subject: Re: [PATCH v1 1/2] scsi: ufs: add required delay after gating
 reference clock

On 2020-02-17 21:12, Stanley Chu wrote:
> Hi Can,
> 
> 
>> >  			} else if (!on && clki->enabled) {
>> >  				clk_disable_unprepare(clki->clk);
>> > +				wait_us = hba->dev_info.clk_gating_wait_us;
>> > +				if (ref_clk && wait_us)
>> > +					usleep_range(wait_us, wait_us + 10);
>> 
>> Hi St,anley,
>> 
>> If wait_us is 1us, it would be inappropriate to use usleep_range() 
>> here.
>> You have checks of the delay in patch #2, but why it is not needed 
>> here?
>> 
>> Thanks,
>> Can Guo.
> 
> You are right. I could make that delay checking as common function so 
> it
> can be used here as well to cover all possible values.
> 
> Thanks for suggestion.
> Stanley

Hi Stanley,

One more thing, as in patch #2, you have already added delays in your
ufshcd_vops_setup_clocks(OFF, PRE_CHANGE) path, plus this delay here,
don't you delay for 2*bRefClkGatingWaitTime in ufshcd_setup_clocks()?
As the delay added in your vops also delays the actions of turning
off all the other clocks in ufshcd_setup_clocks(), you don't need the
delay here again, do you agree?

Thanks,
Can Guo.