Re: [PATCH v7 2/4] usb: dwc3: qcom: Add interconnect support in dwc3 driver

From: "Sandeep Maheswaram (Temp)" <sanm@codeaurora.org>
To: Stephen Boyd <swboyd@chromium.org>,
	Andy Gross <agross@kernel.org>,
	Bjorn Andersson <bjorn.andersson@linaro.org>,
	Doug Anderson <dianders@chromium.org>,
	Felipe Balbi <balbi@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Matthias Kaehlcke <mka@chromium.org>,
	Rob Herring <robh+dt@kernel.org>
Cc: linux-arm-msm@vger.kernel.org, linux-usb@vger.kernel.org,
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
	Manu Gautam <mgautam@codeaurora.org>,
	Chandana Kishori Chiluveru <cchiluve@codeaurora.org>
Subject: Re: [PATCH v7 2/4] usb: dwc3: qcom: Add interconnect support in dwc3 driver
Date: Thu, 4 Jun 2020 15:13:09 +0530	[thread overview]
Message-ID: <d9ccf188-4f00-d3ac-ba0f-73f06c087553@codeaurora.org> (raw)
In-Reply-To: <159120577830.69627.13288547914742515702@swboyd.mtv.corp.google.com>


On 6/3/2020 11:06 PM, Stephen Boyd wrote:
> Quoting Sandeep Maheswaram (2020-03-31 22:15:43)
>> diff --git a/drivers/usb/dwc3/dwc3-qcom.c b/drivers/usb/dwc3/dwc3-qcom.c
>> index 1dfd024..d33ae86 100644
>> --- a/drivers/usb/dwc3/dwc3-qcom.c
>> +++ b/drivers/usb/dwc3/dwc3-qcom.c
>> @@ -76,8 +85,13 @@ struct dwc3_qcom {
>>          enum usb_dr_mode        mode;
>>          bool                    is_suspended;
>>          bool                    pm_suspended;
>> +       struct icc_path         *usb_ddr_icc_path;
>> +       struct icc_path         *apps_usb_icc_path;
>>   };
>>   
>> +static int dwc3_qcom_interconnect_enable(struct dwc3_qcom *qcom);
>> +static int dwc3_qcom_interconnect_disable(struct dwc3_qcom *qcom);
> Please get rid of these. We shouldn't need forward declarations.
Will do in next version.
>
>> +
>>   static inline void dwc3_qcom_setbits(void __iomem *base, u32 offset, u32 val)
>>   {
>>          u32 reg;
>> @@ -285,6 +307,101 @@ static int dwc3_qcom_resume(struct dwc3_qcom *qcom)
>>          return 0;
>>   }
>>   
>> +
>> +/**
>> + * dwc3_qcom_interconnect_init() - Get interconnect path handles
>> + * @qcom:                      Pointer to the concerned usb core.
>> + *
>> + */
>> +static int dwc3_qcom_interconnect_init(struct dwc3_qcom *qcom)
>> +{
>> +       struct device *dev = qcom->dev;
>> +       int ret;
>> +
>> +       if (!device_is_bound(&qcom->dwc3->dev))
>> +               return -EPROBE_DEFER;
> How is this supposed to work? I see that this was added in an earlier
> revision of this patch series but there isn't any mention of why
> device_is_bound() is used here. It would be great if there was a comment
> detailing why this is necessary. It sounds like maximum_speed is
> important?
>
> Furthermore, dwc3_qcom_interconnect_init() is called by
> dwc3_qcom_probe() which is the function that registers the device for
> qcom->dwc3->dev. If that device doesn't probe between the time it is
> registered by dwc3_qcom_probe() and this function is called then we'll
> fail dwc3_qcom_probe() with -EPROBE_DEFER. And that will remove the
> qcom->dwc3->dev device from the platform bus because we call
> of_platform_depopulate() on the error path of dwc3_qcom_probe().
>
> So isn't this whole thing racy and can potentially lead us to a driver
> probe loop where the wrapper (dwc3_qcom) and the core (dwc3) are probing
> and we're trying to time it just right so that driver for dwc3 binds
> before we setup interconnects? I don't know if dwc3 can communicate to
> the wrapper but that would be more of a direct way to do this. Or maybe
> the wrapper should try to read the DT property for maximum speed and
> fallback to a worst case high bandwidth value if it can't figure it out
> itself without help from dwc3 core.
>
This was added in V4 to address comments from Matthias in V3

https://patchwork.kernel.org/patch/11148587/

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