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charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <8ac28471-7c0a-1850-6560-50da0d734445@codeaurora.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 07, 2020 at 10:41:24AM +0530, Sandeep Maheswaram (Temp) wrote: > > 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); Yes, that would get the maximum speed from the DT if it is specified. In case of USB_SPEED_UNKNOWN you probably want to assume it's USB_SPEED_SUPER, which in the worst case would result in the ICC running at a higher speed than needed.