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Tue, 16 Jun 2020 04:52:58 GMT Received: by smtp.codeaurora.org (Postfix, from userid 1001) id BE0E2C43387; Tue, 16 Jun 2020 04:52:58 +0000 (UTC) Received: from [10.206.24.160] (blr-c-bdr-fw-01_GlobalNAT_AllZones-Outside.qualcomm.com [103.229.19.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) (Authenticated sender: sanm) by smtp.codeaurora.org (Postfix) with ESMTPSA id 4E765C433C8; Tue, 16 Jun 2020 04:52:51 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 4E765C433C8 Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; spf=none smtp.mailfrom=sanm@codeaurora.org Subject: Re: [PATCH v7 2/4] usb: dwc3: qcom: Add interconnect support in dwc3 driver To: Matthias Kaehlcke , Stephen Boyd Cc: Andy Gross , Bjorn Andersson , Doug Anderson , Felipe Balbi , Greg Kroah-Hartman , Mark Rutland , Rob Herring , linux-arm-msm@vger.kernel.org, linux-usb@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, Manu Gautam , Chandana Kishori Chiluveru References: <1585718145-29537-1-git-send-email-sanm@codeaurora.org> <1585718145-29537-3-git-send-email-sanm@codeaurora.org> <159120577830.69627.13288547914742515702@swboyd.mtv.corp.google.com> <159126939154.69627.13027312816468830595@swboyd.mtv.corp.google.com> <20200615194239.GW4525@google.com> From: "Sandeep Maheswaram (Temp)" Message-ID: <3f8fcb0e-387d-e902-9f6b-1fde9d6ae404@codeaurora.org> Date: Tue, 16 Jun 2020 10:22:47 +0530 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.8.1 MIME-Version: 1.0 In-Reply-To: <20200615194239.GW4525@google.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/16/2020 1:12 AM, Matthias Kaehlcke wrote: > On Thu, Jun 04, 2020 at 04:16:31AM -0700, Stephen Boyd wrote: >> Quoting Sandeep Maheswaram (Temp) (2020-06-04 02:43:09) >>> 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 >>>>> @@ -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/ >>> >> Yes, that why I said: >> >> "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?" >> >> Can you please respond to the rest of my email? > I agree with Stephen that using device_is_bound() isn't a good option > in this case, when I suggested it I wasn't looking at the big picture > of how probing the core driver is triggered, sorry about that. > > Reading the speed from the DT with usb_get_maximum_speed() as Stephen > suggests would be an option, the inconvenient is that we then > essentially require the property to be defined, while the core driver > gets a suitable value from hardware registers. Not sure if the wrapper > driver could read from the same registers. > > One option could be to poll device_is_bound() for 100 ms (or so), with > sleeps between polls. It's not elegant but would probably work if we > don't find a better solution. if (np)         ret = dwc3_qcom_of_register_core(pdev);     else         ret = dwc3_qcom_acpi_register_core(pdev);     if (ret) {         dev_err(dev, "failed to register DWC3 Core, err=%d\n", ret);         goto depopulate;     }     ret = dwc3_qcom_interconnect_init(qcom);     if (ret)         goto depopulate;     qcom->mode = usb_get_dr_mode(&qcom->dwc3->dev); Before calling dwc3_qcom_interconnect_init we are checking     if (ret) {         dev_err(dev, "failed to register DWC3 Core, err=%d\n", ret);         goto depopulate;     } Doesn't  this condition confirm the core driver is probed? -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation