linux-kernel - Re: [PATCH v2 07/10] phy: qcom-qmp: Add support for DP in USB3+DP combo phy

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Message-ID: <c8ca7193-67ae-e1d5-d36a-19655ca67d78@linaro.org>
Date:   Fri, 4 Sep 2020 15:57:21 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Jonathan Marek <jonathan@...ek.ca>,
        Stephen Boyd <swboyd@...omium.org>,
        Kishon Vijay Abraham I <kishon@...com>,
        Vinod Koul <vkoul@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        Jeykumar Sankaran <jsanka@...eaurora.org>,
        Chandan Uddaraju <chandanu@...eaurora.org>,
        Vara Reddy <varar@...eaurora.org>,
        Tanmay Shah <tanmay@...eaurora.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Manu Gautam <mgautam@...eaurora.org>,
        Sandeep Maheswaram <sanm@...eaurora.org>,
        Douglas Anderson <dianders@...omium.org>,
        Sean Paul <seanpaul@...omium.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Rob Clark <robdclark@...omium.org>
Subject: Re: [PATCH v2 07/10] phy: qcom-qmp: Add support for DP in USB3+DP
 combo phy

On 04/09/2020 15:44, Jonathan Marek wrote:
> On 9/4/20 8:29 AM, Dmitry Baryshkov wrote:
>> On 03/09/2020 23:43, Jonathan Marek wrote:
>>> On 9/2/20 7:02 PM, Stephen Boyd wrote:
>>>> Add support for the USB3 + DisplayPort (DP) "combo" phy to the qmp phy
>>>> driver. We already have support for the USB3 part of the combo phy, so
>>>> most additions are for the DP phy.
>>>>
>>>> Split up the qcom_qmp_phy{enable,disable}() functions into the phy 
>>>> init,
>>>> power on, power off, and exit functions that the common phy framework
>>>> expects so that the DP phy can add even more phy ops like
>>>> phy_calibrate() and phy_configure(). This allows us to initialize 
>>>> the DP
>>>> PHY and configure the AUX channel before powering on the PHY at the 
>>>> link
>>>> rate that was negotiated during link training.
>>>>
>>>> The general design is as follows:
>>>>
>>>>    1) DP controller calls phy_init() to initialize the PHY and 
>>>> configure
>>>>    the dp_com register region.
>>>>
>>>>    2) DP controller calls phy_configure() to tune the link rate and
>>>>    voltage swing and pre-emphasis settings.
>>>>
>>>>    3) DP controller calls phy_power_on() to enable the PLL and power on
>>>>    the phy.
>>>>
>>>>    4) DP controller calls phy_configure() again to tune the voltage 
>>>> swing
>>>>    and pre-emphasis settings determind during link training.
>>>>
>>>>    5) DP controller calls phy_calibrate() some number of times to 
>>>> change
>>>>    the aux settings if the aux channel times out during link training.
>>>>
>>>>    6) DP controller calls phy_power_off() if the link rate is to be
>>>>    changed and goes back to step 2 to try again at a different link 
>>>> rate.
>>>>
>>>>    5) DP controller calls phy_power_off() and then phy_exit() to power
>>>>    down the PHY when it is done.
>>>>
>>>> The DP PHY contains a PLL that is different from the one used for the
>>>> USB3 PHY. Instead of a pipe clk there is a link clk and a pixel clk
>>>> output from the DP PLL after going through various dividers. Introduce
>>>> clk ops for these two clks that just tell the child clks what the
>>>> frequency of the pixel and link are. When the phy link rate is
>>>> configured we call clk_set_rate() to update the child clks in the
>>>> display clk controller on what rate is in use. The clk frequencies
>>>> always differ based on the link rate (i.e. 1.6Gb/s 2.7Gb/s, 5.4Gb/s, or
>>>> 8.1Gb/s corresponding to various transmission modes like HBR1, HBR2 or
>>>> HBR3) so we simply store the link rate and use that to calculate the 
>>>> clk
>>>> frequencies.
>>>>
>>>> The PLL enable sequence is a little different from other QMP phy 
>>>> PLLs so
>>>> we power on the PLL in qcom_qmp_phy_configure_dp_phy() that gets called
>>>> from phy_power_on(). This should probably be split out better so that
>>>> each phy has a way to run the final PLL/PHY enable sequence.
>>>>
>>>> This code is based on a submission of this phy and PLL in the drm
>>>> subsystem.
>>>
>>> I updated my upstream-based sm8150/sm8250 displayport stack [1] to 
>>> use these patches.
>>
>> I have tried your branch on my RB5 with two different dongles. Both 
>> dongles provide the same behaviour:
>>   - on first plug I see VDM Tx errors,
>>   - after I unplug and replug the dongle, PD phy seems to be stuck on 
>> sending capabilities.
>>
>> See attached logs.
>>
>> Also I had to add typec_unregister_port(port->typec_port); to 
>> IS_ERR(alt) in your tcpm.c hack.
>>
>> I'm currently finishing the driver for the mux/redriver, will retry 
>> testing afterwards.
>>
> 
> As I mentioned the TCPM driver has a lot of issues. The "hard reset" 
> isn't implemented correctly so going into that mode gets it stuck in a 
> bad state. Note I am using this dongle [1], and it only works correctly 
> in sink mode (with the dongle providing power), in source mode it does 
> negotiate the alt mode, but never gets the HPD event that DP driver is 
> waiting for.
> 
> https://www.amazon.ca/Cable-Matters-Multiport-DisplayPort-Ethernet/dp/B06Y5N3YCD 

I'll take a look for dongles that work in source mode (with RB5 being 
the sink). Reset being not fully implemented would answer on questions 
about replug. Any idea about VDM Tx errors?


-- 
With best wishes
Dmitry