Messages in this thread | | | Subject | Re: [PATCH v7 2/4] usb: dwc3: qcom: Add interconnect support in dwc3 driver | From | "Sandeep Maheswaram (Temp)" <> | Date | Tue, 16 Jun 2020 10:22:47 +0530 |
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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?
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