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From:   Doug Anderson <dianders@chromium.org>
Date:   Tue, 27 Mar 2018 13:14:31 -0700
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Subject: Re: [PATCH v3 1/6] phy: qcom-qmp: Enable pipe_clk before checking
 USB3 PHY_STATUS
To:     Manu Gautam <mgautam@codeaurora.org>
Cc:     Vivek Gautam <vivek.gautam@codeaurora.org>,
        Kishon Vijay Abraham I <kishon@ti.com>,
        LKML <linux-kernel@vger.kernel.org>, devicetree@vger.kernel.org,
        Rob Herring <robh+dt@kernel.org>,
        linux-arm-msm@vger.kernel.org,
        Varadarajan Narayanan <varada@codeaurora.org>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Wei Yongjun <weiyongjun1@huawei.com>,
        Fengguang Wu <fengguang.wu@intel.com>,
        Amit Nischal <anischal@codeaurora.org>
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Hi,

On Tue, Mar 27, 2018 at 12:50 AM, Manu Gautam <mgautam@codeaurora.org> wrote:
> Hi,
>
>
> On 3/27/2018 12:26 PM, Vivek Gautam wrote:
>>
>>
>> On 3/27/2018 10:37 AM, Manu Gautam wrote:
>>> Hi Doug,
>>>
>>>
>>> On 3/27/2018 9:56 AM, Doug Anderson wrote:
>>>> Manu
>>>>
>>>> On Thu, Mar 22, 2018 at 11:11 PM, Manu Gautam <mgautam@codeaurora.org> wrote:
>>>>> QMP PHY for USB mode requires pipe_clk for calibration and PLL lock
>>>>> to take place. This clock is output from PHY to GCC clock_ctl and then
>>>>> fed back to QMP PHY and is available from PHY only after PHY is reset
>>>>> and initialized, hence it can't be enabled too early in initialization
>>>>> sequence.
>>>>>
>>>>> Signed-off-by: Manu Gautam <mgautam@codeaurora.org>
>>>>> ---
>>>>>   drivers/phy/qualcomm/phy-qcom-qmp.c | 33 ++++++++++++++++++++++++++++++++-
>>>>>   1 file changed, 32 insertions(+), 1 deletion(-)
>>>> So it's now new with this patch, but it's more obvious with this
>>>> patch.  It seems like "UFS/PCIE" is kinda broken w/ respect to how it
>>>> controls its clock.  Specifically:
>>>>
>>>> * If you init the PHY but don't power it on, then you "exit" the PHY:
>>>> you'll disable/unprepare "pipe_clk" even though you never
>>>> prepare/enabled it.
>>>>
>>>> * If you init the PHY, power it on, power it off, power it on, and
>>>> exit the PHY: you'll leave the clock prepared one extra time.
>>>>
>>>> Specifically I'd expect: for UFS/PCIE the disable/unprepare should be
>>>> symmetric with the enable/prepare and should be in "power off", not in
>>>> exit.
>>>>
>>>> ...or did I miss something?
>>>>
>>>>
>>>> Interestingly, your patch fixes this problem for USB3 (where init/exit
>>>> are now symmetric), but leaves the problem there for UFS/PCIE.
>>>>
>>> Thanks for review.
>>> One of the reason why pipe_clk is disabled as part of phy_exit is that
>>> halt_check from clk_disable reports error if called after PHY has been
>>> powered down or phy_exit.
>>> I believe that warning should be ignored in qcom gcc-clock driver
>>> (for applicable platforms) by using BRANCH_HALT_DELAY as halt_check
>>> for pipe_clk and performing clk_disable from power_off for UFS/PCIE.
>> UFS doesn't use PIPE clock.

Just to confirm: we no longer need to do this "BRANCH_HALT_DELAY" now
that we've figured everything out, right?


> Yes, UFS PHY doesn't use one. But similar to pipe_clk there are rx/tx symbol_clk
> output from PHY that is used by UFS controller. I will update code comments
> to not refer UFS for pipe_clk.
>
>> But considering for PCIe, if we disable pipe clock when phy is still running, then
>> it shouldn't be a problem. We should also not see the halt warning as the gcc
>> driver should be able to just turn the gate off.
>> The reason why it will throw that error is when the parent clock to that gate
>> is gated, i.e. the pipe clock is not flowing on that branch.
>
> I got the confirmation that pipe_clk is needed for PCIE as well for its
> initialization to happen successfully. So we do need clock driver change
> to fix this in PHY driver.

So basically if I'm understanding this correctly:

* Both USB and PCIE need the clk_enable() in qcom_qmp_phy_init()

* UFS doesn't even use a pipe clock (pipe_clk is NULL and thus these
calls are no-ops).

So that means the next version of this code will simply get rid of
qcom_qmp_phy_poweron() and we can now use the same phy_ops for both
everything again?  That also makes everything symmetric and gets rid
of the possible imbalance of clock enable/disable, so I'm happy.


Actually: I'll also throw out a drastic idea here.  Maybe instead of
having a NULL power_on/power_off, we should have a NULL init/exit.
Does anything break if all the stuff that happens today in
qcom_qmp_phy_com_init() happens at power_on() time instead of init()
time?  I suggest this because:

* It sounds like init() is supposed to be for initialization that can
happen _before_ power on of the PHY.

* Any initialization that happens after the PHY has been powered on
seems expected to just be in the power_on() function after the
regulator was enabled.


Presumably moving this stuff to power_on could save you some power in
some cases (since the client of the PHY presumably turns power off to
the PHY with the idea of saving power).


-Doug