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

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Message-ID: <1582103495.26304.42.camel@mtksdccf07>
Date:   Wed, 19 Feb 2020 17:11:35 +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 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?

> 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.

Thanks,
Stanley Chu