Re: [PATCH] usb: roles: Add PM callbacks

[Hans de Goede]

Hi,

On 08-07-19 04:25, Chen, Hu wrote:

On some Broxton NUC, the usb role is lost after S3 (it becomes "none").
Add PM callbacks to address this issue: save the role during suspend and
restore usb to that role during resume.

Test:
Run Android on UC6CAY, a NUC powered by Broxton. Access this NUC via
"adb shell" from a host PC. After a suspend/resume cycle, the adb still
works well.

Signed-off-by: Chen, Hu <hu1.c...@intel.com>
Signed-off-by: Balaji <m.bal...@intel.com>

Hmm, but what if the user has say unplugged a host-adapter with a usb-stick
in there and plugged in a cable to a computer *while suspended* because the
battery was getting low?

I see 2 scenarios here:

1) We may get an interrupt for the role change, followed by an
intel_xhci_usb_set_role. In this case the interrupt handling may happen
before the intel_xhci_usb_resume call and we would end up restoring the
wrong value

2) The role may be changed underneath us by the firmware / AML code
without us ever becoming aware of this.

For the specific problem discussed in the commit message it might be better
to do something like:

static int intel_xhci_usb_resume(struct platform_device *pdev)
{
        struct intel_xhci_usb_data *data = platform_get_drvdata(pdev);
        struct device *dev = &pdev->dev;

        if (intel_xhci_usb_get_role(dev) == USB_ROLE_NONE &&
            power_supply_is_system_supplied())
                intel_xhci_usb_set_role(dev, USB_ROLE_DEVICE);

        return 0;
}

But that is somewhat specific for solving the problem described in
the commit message, but it has the advantage of not being able to
cause any regressions (that I can think of).

Regards,

Hans

diff --git a/drivers/usb/roles/intel-xhci-usb-role-switch.c 
b/drivers/usb/roles/intel-xhci-usb-role-switch.c
index 277de96181f9..caa1cfab41cc 100644
--- a/drivers/usb/roles/intel-xhci-usb-role-switch.c
+++ b/drivers/usb/roles/intel-xhci-usb-role-switch.c
@@ -37,6 +37,7 @@
  struct intel_xhci_usb_data {
        struct usb_role_switch *role_sw;
        void __iomem *base;
+       enum usb_role role;
  };

static int intel_xhci_usb_set_role(struct device *dev, enum usb_role role)

@@ -167,6 +168,30 @@ static int intel_xhci_usb_remove(struct platform_device 
*pdev)
        return 0;
  }

+static int intel_xhci_usb_suspend(struct platform_device *pdev,

+                                 pm_message_t state)
+{
+       struct intel_xhci_usb_data *data = platform_get_drvdata(pdev);
+       struct device *dev = &pdev->dev;
+
+       data->role = intel_xhci_usb_get_role(dev);
+
+       return 0;
+}
+
+static int intel_xhci_usb_resume(struct platform_device *pdev)
+{
+       struct intel_xhci_usb_data *data = platform_get_drvdata(pdev);
+       struct device *dev = &pdev->dev;
+
+       if (intel_xhci_usb_get_role(dev) != data->role) {
+               if (intel_xhci_usb_set_role(dev, data->role) != 0)
+                       dev_warn(dev, "Failed to set role during resume\n");
+       }
+
+       return 0;
+}
+
  static const struct platform_device_id intel_xhci_usb_table[] = {
        { .name = DRV_NAME },
        {}
@@ -180,6 +205,8 @@ static struct platform_driver intel_xhci_usb_driver = {
        .id_table = intel_xhci_usb_table,
        .probe = intel_xhci_usb_probe,
        .remove = intel_xhci_usb_remove,
+       .suspend = intel_xhci_usb_suspend,
+       .resume = intel_xhci_usb_resume,
  };

module_platform_driver(intel_xhci_usb_driver);