linux-kernel - Re: [PATCH v7 7/8] scsi: ufs-qcom: Delay specific time before gate ref clk

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Message-ID: <9de3632cf0c65347684b8c5f4f3c63b3@codeaurora.org>
Date:   Fri, 07 Feb 2020 09:09:36 +0800
From:   Can Guo <cang@...eaurora.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     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,
        Andy Gross <agross@...nel.org>,
        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>,
        "open list:ARM/QUALCOMM SUPPORT" <linux-arm-msm@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7 7/8] scsi: ufs-qcom: Delay specific time before gate
 ref clk

On 2020-02-07 04:33, Bjorn Andersson wrote:
> On Thu 06 Feb 00:33 PST 2020, Can Guo wrote:
> 
>> After enter hibern8, as UFS JEDEC ver 3.0 requires, a specific gating 
>> wait
>> time is required before disable the device reference clock. If it is 
>> not
>> specified, use the old delay.
>> 
>> Signed-off-by: Can Guo <cang@...eaurora.org>
>> Reviewed-by: Asutosh Das <asutoshd@...eaurora.org>
>> Reviewed-by: Hongwu Su <hongwus@...eaurora.org>
>> ---
>>  drivers/scsi/ufs/ufs-qcom.c | 22 +++++++++++++++++++---
>>  1 file changed, 19 insertions(+), 3 deletions(-)
>> 
>> diff --git a/drivers/scsi/ufs/ufs-qcom.c b/drivers/scsi/ufs/ufs-qcom.c
>> index 85d7c17..39eefa4 100644
>> --- a/drivers/scsi/ufs/ufs-qcom.c
>> +++ b/drivers/scsi/ufs/ufs-qcom.c
>> @@ -833,6 +833,8 @@ static int ufs_qcom_bus_register(struct 
>> ufs_qcom_host *host)
>> 
>>  static void ufs_qcom_dev_ref_clk_ctrl(struct ufs_qcom_host *host, 
>> bool enable)
>>  {
>> +	unsigned long gating_wait;
>> +
>>  	if (host->dev_ref_clk_ctrl_mmio &&
>>  	    (enable ^ host->is_dev_ref_clk_enabled)) {
>>  		u32 temp = readl_relaxed(host->dev_ref_clk_ctrl_mmio);
>> @@ -845,11 +847,25 @@ static void ufs_qcom_dev_ref_clk_ctrl(struct 
>> ufs_qcom_host *host, bool enable)
>>  		/*
>>  		 * If we are here to disable this clock it might be immediately
>>  		 * after entering into hibern8 in which case we need to make
>> -		 * sure that device ref_clk is active at least 1us after the
>> +		 * sure that device ref_clk is active for specific time after
>>  		 * hibern8 enter.
>>  		 */
>> -		if (!enable)
>> -			udelay(1);
>> +		if (!enable) {
>> +			gating_wait = host->hba->dev_info.clk_gating_wait_us;
>> +			if (!gating_wait) {
> 
> Afaict this can't happen, because in patch 6 you check for gating_wait
> being 0 and if so set it to 0xff.
> 

Sorry, I was intended to give clk_gating_wait_us values only if it is
a UFS3.0 device. I will revise patch 6/8.

>> +				udelay(1);
>> +			} else {
>> +				/*
>> +				 * bRefClkGatingWaitTime defines the minimum
>> +				 * time for which the reference clock is
>> +				 * required by device during transition from
>> +				 * HS-MODE to LS-MODE or HIBERN8 state. Give it
>> +				 * more time to be on the safe side.
>> +				 */
>> +				gating_wait += 10;
>> +				usleep_range(gating_wait, gating_wait + 10);
> 
> I presume there's no strong requirement on the max, so how about using 
> a
> substantially larger max - say 1k, or 10k - to allow the usleep_range()
> to do it's job?
> 
> 
> PS. Please include linux-arm-msm@ on all the patches in the series, not
> just two of them.
> 
> Regards,
> Bjorn
> 

bRefClkGatingWaitTime, as vendor defined in their device attribute is 
usually
around 50~100, 1k or 10k delay makes it too large. usleep_range() works 
well
so long as the delay is within (10us - 20ms), so I added 10 to make sure 
it is
above 10us.

SLEEPING FOR ~USECS OR SMALL MSECS ( 10us - 20ms):
	* Use usleep_range
https://www.kernel.org/doc/Documentation/timers/timers-howto.txt

Thanks,

Can Guo.

>> +			}
>> +		}
>> 
>>  		writel_relaxed(temp, host->dev_ref_clk_ctrl_mmio);
>> 
>> --
>> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora 
>> Forum,
>> a Linux Foundation Collaborative Project