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

Stanley Chu
2020-02-20T13:30:52Z

Hi Can,

On Wed, 2020-02-19 at 18:33 +0800, Can Guo wrote:
> Hi Stanley,
>
> On 2020-02-19 17:11, Stanley Chu wrote:
> > Hi Can,
> >
> > On Wed, 2020-02-19 at 10:35 +0800, Can Guo wrote:
> >
> >> 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().
> >>
> >
> > Always putting the delay in the entrance of ufshcd_setup_clocks() may
> > add unwanted delay for vendors, just like your current implementation,
> > or some other vendors who do not want to disable the reference clock.
> >
> > I think current patch is more reasonable because the delay is applied
> > to
> > clock only named as "ref_clk" specifically.
> >
> > If you needs to keep "ref_clk" in DT, would you consider to remove the
> > delay in your ufs_qcom_dev_ref_clk_ctrl() and let the delay happens via
> > common ufshcd_setup_clocks() only? However you may still need delay if
> > call path comes from ufs_qcom_pwr_change_notify().
> >
> > What do you think?
> >
>
> I agree current change is more reasonable from what it looks, but the
> fact
> is that I canont remove the delay in ufs_qcom_dev_ref_clk_ctrl() even
> with
> this change. On our platforms, ref_clk in DT serves multipule purposes,
> the ref_clk provided to UFS device is actually controlled in
> ufs_qcom_dev_ref_clk_ctrl(), which comes before where this change kicks
> start,
> so if I remove the delay in ufs_qcom_dev_ref_clk_ctrl(), this change
> cannot
> provide us the correct delay before gate the ref_clk provided to UFS
> device.

> > Always putting the delay in the entrance of ufshcd_setup_clocks() may
> > add unwanted delay for vendors, just like your current implementation,
> > or some other vendors who do not want to disable the reference clock.
>
> I meant if we put the delay in the entrance, I will be able to remove
> the delay in ufs_qcom_dev_ref_clk_ctrl(). Meanwhile, we can add proper
> checks before the delay to make sure it is initiated only if ref_clk
> needs
> to be disabled, i.e:
>
> if(!on && !skip_ref_clk && hba->dev_info.clk_gating_wait_us)
> usleep_range();
>
> Does this look better to you?

Firstly thanks so much for above details.

Again this statement may also add unwanted delay if some other vendors
does not have "ref_clk" in DT or they don't/can't disable the reference
clock provided to UFS device.

>
> Anyways, we will see regressions with this change on our platforms, can
> we
> have more discussions before get it merged? It should be OK if you go
> with
> patch #2 alone first, right? Thanks.

Now the fact is that this change will impact your flow and it seems no
solid conclusion yet. Sure I could drop patch #1 and submit patch #2
only first : )

Thanks,
Stanley Chu