linux-kernel - Re: [PATCH v3 1/6] phy: qcom-qmp: Enable pipe_clk before checking USB3 PHY

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Date:   Mon, 26 Mar 2018 21:26:49 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Manu Gautam <mgautam@...eaurora.org>
Cc:     Kishon Vijay Abraham I <kishon@...com>,
        LKML <linux-kernel@...r.kernel.org>, devicetree@...r.kernel.org,
        Rob Herring <robh+dt@...nel.org>,
        linux-arm-msm@...r.kernel.org,
        Vivek Gautam <vivek.gautam@...eaurora.org>,
        Varadarajan Narayanan <varada@...eaurora.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Wei Yongjun <weiyongjun1@...wei.com>,
        Fengguang Wu <fengguang.wu@...el.com>
Subject: Re: [PATCH v3 1/6] phy: qcom-qmp: Enable pipe_clk before checking
 USB3 PHY_STATUS

Manu

On Thu, Mar 22, 2018 at 11:11 PM, Manu Gautam <mgautam@...eaurora.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@...eaurora.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.

-Doug