linux-kernel - Re: [PATCH v5 6/8] scsi: ufs: Add dev ref clock gating wait time support

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Message-ID: <1580950556.27391.11.camel@mtksdccf07>
Date:   Thu, 6 Feb 2020 08:55:56 +0800
From:   Stanley Chu <stanley.chu@...iatek.com>
To:     Can Guo <cang@...eaurora.org>
CC:     <kuohong.wang@...iatek.com>, <asutoshd@...eaurora.org>,
        <nguyenb@...eaurora.org>, <hongwus@...eaurora.org>,
        <rnayak@...eaurora.org>, <linux-scsi@...r.kernel.org>,
        <kernel-team@...roid.com>, <saravanak@...gle.com>,
        <salyzyn@...gle.com>, Alim Akhtar <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Bean Huo <beanhuo@...ron.com>,
        Colin Ian King <colin.king@...onical.com>,
        Tomas Winkler <tomas.winkler@...el.com>,
        "Bart Van Assche" <bvanassche@....org>,
        Venkat Gopalakrishnan <venkatg@...eaurora.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 6/8] scsi: ufs: Add dev ref clock gating wait time
 support

Hi Can,

On Wed, 2020-02-05 at 12:52 +0800, Can Guo wrote:

> Hi Stanley,
> 
> We used to ask vendors about it, 50 is somehow agreed by them. Do you 
> have a
> better value in mind?
> 
> For me, I just wanted to give it 10, so that we can directly use 
> usleep_range
> with it, no need to decide whether to use udelay or usleep_range.

Actually I do not have any value in mind because I guess the 50us here
is just a margin time added for safety as your comments: "Give it more
time to be on the safe side".

An example case is that some vendors only specify 1us in
bRefClkGatingWaitTime, so this 50us may be too long compared to device's
requirement. If such device really needs this additional 50us, it shall
be specified in bRefClkGatingWaitTime.

So if this additional delay does not have any special reason or not
mentioned by UFS specification, would you consider move it to vendor
specific implementations. By this way, it would be more flexible to be
controlled by vendors or by platforms.

Thanks,
Stanley

> 
> Thanks,
> Can Guo.
> 
> >>  				      &dev_info->model, SD_ASCII_STD);