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

[Can Guo]

Hi Stanely,

On 2020-02-17 21:42, Can Guo wrote:
> 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.

Since we all need this delay here, how about put the delay in the
entrence of ufshcd_setup_clocks(), before vops_setup_clocks()?
If so, we can remove all the delays we added in our vops since the
delay anyways delays everything inside ufshcd_setup_clocks().

Meanwhile, if you want to modify the delay
(hba->dev_info.clk_gating_wait_us) for some reasons, say for specific
UFS devices, you still can do it in vops_apply_dev_quirks().

What do you say?

Thanks,
Can Guo.