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

Can Guo
2020-02-07T01:09:44Z

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@codeaurora.org>
>> Reviewed-by: Asutosh Das <asutoshd@codeaurora.org>
>> Reviewed-by: Hongwu Su <hongwus@codeaurora.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