On 6/16/2020 1:12 AM, Matthias Kaehlcke wrote:

On Thu, Jun 04, 2020 at 04:16:31AM -0700, Stephen Boyd wrote:

quoted

Quoting Sandeep Maheswaram (Temp) (2020-06-04 02:43:09)

quoted

On 6/3/2020 11:06 PM, Stephen Boyd wrote:

quoted

Quoting Sandeep Maheswaram (2020-03-31 22:15:43)

quoted

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