Messages in this thread | | | Date | Sat, 08 Feb 2020 08:10:55 +0800 | From | Can Guo <> | Subject | Re: [PATCH v7 7/8] scsi: ufs-qcom: Delay specific time before gate ref clk |
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On 2020-02-07 10:10, Bjorn Andersson wrote: > On Thu 06 Feb 17:09 PST 2020, Can Guo wrote: > >> 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. >> > > Okay, sounds good. > >> > > + 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. >> > > I meant specifically the second parameter, i.e: > usleep_range(bRefClkGatingWaitTime + 10, bRefClkGatingWaitTime + > 1000); > > As you're not guaranteed an upper bound of this sleep anyway you might > as well give usleep_range() a window of a millisecond (or more) to give > it the flexibility of matching other timer events. > > The only drawback with this is that you might "waste" a millisecond. > > Regards, > Bjorn >
Hi Bjorn,
Device ref clk gate/ungate can happen very frequently if clk gating is enabled. The "wasted" milliseconds might be accumulated to affect read/write latency, i.e:
If read/write requests come, clk ungate kicks start, it flushes ongoing gate work if any, if we "waste" a millisecond here, the read/write requests will be delayed a millisecond. I am not sure how much it may impact the overall performance in a long term test.
Thanks,
Can Guo.
>> 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
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