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 21:34:09 +0800
From:   Stanley Chu <stanley.chu@...iatek.com>
To:     Can Guo <cang@...eaurora.org>
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

Hi Can,

On Mon, 2020-02-17 at 21:22 +0800, Can Guo wrote:
> 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?

MediaTek driver is not using reference clocks named as "ref_clk" defined
in device tree, thus the delay specific for "ref_clk" in
ufshcd_setup_clocks() will not be applied in MediaTek platform.

This patch is aimed to add delay for this kind of "ref_clk" used by any
future vendors.

Anyway thanks for the reminding : )

> 
> Thanks,
> Can Guo.


Thanks,
Stanley