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, 7 Jul 2020 10:41:24 +0530 |
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On 7/1/2020 4:12 AM, Matthias Kaehlcke wrote: > On Tue, Jun 16, 2020 at 01:38:49PM -0700, Matthias Kaehlcke wrote: >> On Tue, Jun 16, 2020 at 10:22:47AM +0530, Sandeep Maheswaram (Temp) wrote: >>> 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? >> Not really: >> >> // called under the hood by of_platform_populate() >> static int really_probe(struct device *dev, struct device_driver *drv) >> { >> ... >> >> if (dev->bus->probe) { >> ret = dev->bus->probe(dev); >> if (ret) >> goto probe_failed; >> } else if (drv->probe) { >> ret = drv->probe(dev); >> if (ret) >> goto probe_failed; >> } >> >> ... >> >> probe_failed: >> ... >> >> /* >> * Ignore errors returned by ->probe so that the next driver can try >> * its luck. >> */ >> ret = 0; >> >> ... >> >> return ret; >> } >> >> As a result of_platform_populate() in dwc3_qcom_of_register_core() >> returns 0 even when probing the device failed: >> >> [ 0.244339] dwc3-qcom a6f8800.usb: DBG: populate >> [ 0.244772] dwc3 a600000.dwc3: DBG: dwc3_probe >> [ 0.245237] dwc3 a600000.dwc3: DBG: dwc3_probe err: -517 >> [ 0.245264] dwc3-qcom a6f8800.usb: DBG: populate (done) >> [ 0.245317] dwc3-qcom a6f8800.usb: DBG: dwc3_qcom_interconnect_init() failed: -517 >> >> Probe fails because the interconnect stuff isn't ready yet, otherwise >> it could access invalid data. >> >> A later _populate() is successful and the probing of the core is done >> synchronously, i.e. after _populate() the core driver is fully >> initialized: >> >> [ 3.898106] dwc3-qcom a6f8800.usb: DBG: populate >> [ 3.908356] dwc3 a600000.dwc3: DBG: dwc3_probe >> [ 4.205104] dwc3 a600000.dwc3: DBG: dwc3_probe (done) >> [ 4.210305] dwc3-qcom a6f8800.usb: DBG: populate (done) >> >> The synchronous probing in _populate() suggests that using device_is_bound() >> would actually be a valid option, either the core device was successfully >> probed or not, there should be no race. >> >> I sent a patch that adds this check to dwc3_qcom_of_register_core(), which >> is less confusing and makes clear that the core device is valid unless >> this function returns an error: >> >> https://lore.kernel.org/patchwork/patch/1257279/ >> >> It might make sense to add your "driver core:Export the symbol >> device_is_bound" patch, mine and this one to a single series. > From the discussion on "driver core:Export the symbol device_is_bound" > (https://patchwork.kernel.org/patch/11584225/) it is clear that > this won't fly. The split dwc3 driver is considered a broken > design. > > This is what Rob Herring said: > > We never should have had this split either in the DT binding nor > driver(s) as if the SoC wrapper crap and licensed IP block are > independent things. The thing to do here is either make the DWC3 code > a library which drivers call (e.g. SDHCI) or add hooks into the DWC3 > driver for platform specifics (e.g. Designware PCI). Neither is a > simple solution though. > > That seems to be the desirable solution in the longer term, but it > doesn't seem reasonable to me to expect you to fix this design issue > to add interconnect support. > > Some possible options to move forward: > > - try to determine the max speed without involving the core device > - select a reasonable default when 'maximum-speed' is not specified > - use the core device to determine the max speed and pray
Can we do as below to get speed
qcom->max_speed = usb_get_maximum_speed(&qcom->dwc3->dev);
as they were doing similarly in below code to get mode
qcom->mode = usb_get_dr_mode(&qcom->dwc3->dev);
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