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

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Message-ID: <8b6603db0bb793365542c39d33a64a0e@codeaurora.org>
Date:   Thu, 06 Feb 2020 10:39:57 +0800
From:   Can Guo <cang@...eaurora.org>
To:     Stanley Chu <stanley.chu@...iatek.com>
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

On 2020-02-06 08:55, Stanley Chu wrote:
> 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);

Hi Stanley,

FYI, the default values in bRefClkGatingWaitTime from vendors are around
50 - 100.

I agree with you. I will just remove the extra delay here and let's
handle it in our own platform drivers.

Thanks,
Can Guo.