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 21:42:35 +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 21:34, Stanley Chu wrote:
> 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

Hi Stanley,

Then we are unluckily hit by this change. We have ref_clk in DT, thus
this change would add unwanted delays to our platforms. but still we
disable device's ref_clk in vops. :)

Could you please hold on patch #1 first? I need sometime to have a
dicussion with my colleagues on this.

Thanks.
Can Guo.