Date:   Fri, 31 Mar 2017 14:50:49 +0300
From:   Roger Quadros <rogerq@...com>
To:     Felipe Balbi <balbi@...nel.org>
CC:     <vivek.gautam@...eaurora.org>, <linux-usb@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        Mathias Nyman <mathias.nyman@...ux.intel.com>
Subject: Re: [PATCH v2 4/4] usb: dwc3: Workaround for super-speed host on dra7
 in dual-role mode

+Mathias

On 31/03/17 10:46, Felipe Balbi wrote:
> 
> Hi,
> 
> Roger Quadros <rogerq@...com> writes:
>>>>> Roger Quadros <rogerq@...com> writes:
>>>>>> dra7 OTG core limits the host controller to USB2.0 (high-speed) mode
>>>>>> when we're operating in dual-role.
>>>>>
>>>>> yeah, that's not a quirk. DRA7 supports OTGv2, not OTGv3. There was no
>>>>> USB3 when OTGv2 was written.
>>>>>
>>>>> DRA7 just shouldn't use OTG core altogether. In fact, this is the very
>>>>> thing I've been saying for a long time. Make the simplest implementation
>>>>> possible. The dead simple, does-one-thing-only sort of implementation.
>>>>>
>>>>> All we need for Dual-Role (without OTG extras) is some input for ID and
>>>>> VBUS, then we add/remove HCD/UDC conditionally and set PRTCAPDIR.
>>>>>
>>>>
>>>> The catch is that on AM437x there is no way to get ID and VBUS events other
>>>> than the OTG controller so we have to rely on the OTG controller for that. :(
>>>
>>> okay, so AM437x can get OTG interrupts properly. That's fine. We can
>>> still do everything we need using code that's already existing in dwc3
>>> if we refactor it a bit and hook it up to the OTG IRQ handler.
>>>
>>> Here's what we do:
>>>
>>> * First we re-factor all necessary code around so the API for OTG/DRD
>>>   is resumed to calling:
>>>
>>> 	dwc3_add_udc(dwc);
>>>         dwc3_del_udc(dwc);
>>>         dwc3_add_hcd(dwc);
>>>         dwc3_del_hcd(dwc);
>>
>> Why do we need these new APIs? don't these suffice?
>> 	dwc3_gadget_init(dwc);
>> 	dwc3_gadget_exit(dwc);
>> 	dwc3_host_init(dwc);
>> 	dwc3_host_exit(dwc);
> 
> well, if they do what we want, sure. They suffice.
> 
>>> the semantics of these should be easy to understand and you can
>>> implement each in their respective host.c/gadget.c files.
>>>
>>> * Second step is to modify our dwc3_init_mode() (or whatever that
>>>   function was called, sorry, didn't check) to make sure we have
>>>   something like:
>>>
>>> 	case OTG:
>>>         	dwc3_add_udc(dwc);
>>>                 break;
>>>
>>> We should *not* add HCD in this case yet.
>>>
>>> * After that we add otg.c (or drd.c, no preference) and make that call
>>>   dwc3_add_udc(dwc) and, also, provide
>>>   dwc3_add_otg(dwc)/dwc3_del_otg(dwc) calls. Then patch the switch
>>>   statement above to:
>>>
>>> 	case OTG:
>>>         	dwc3_add_otg(dwc);
>>>                 break;
>>>
>>> Note that at this point, this is simply a direct replacement of
>>> dwc3_add_udc() to dwc3_add_otg(). This should maintain current behavior
>>> (which is starting with peripheral mode by default), but it should also
>>> add support for OTG interrupts to change the mode (from an interrupt
>>> thead)
>>>
>>> 	otg_isr()
>>>         {
>>>
>>> 		/* don't forget to remove preivous mode if necessary */
>>>         	if (perimode)
>>>                 	dwc3_add_udc(dwc);
>>>                 else
>>>                 	dwc3_add_hcd(dwc);
>>> 	}
>>>
>>> * The next patch would be to choose default conditionally based on
>>>   PERIMODE or whatever.
>>>
>>> Of course, this is an oversimplified view of reality. You still need to
>>> poke around at PRTCAPDIR, etc. But all this can, actually, be prototyped
>>> using our "mode" debugfs file. Just make that call
>>> dwc3_add/del_udc/hcd() apart from fiddling with PRTCAPDIR in GCTL.
>>
>> We also need to ensure that system suspend/resume doesn't break.
>> Mainly if we suspend/resume with UDC removed.
> 
> right, why would it break in that case? I'm missing something...
> 
>>> Your first implementation could be just that. Refactoring what needs to
>>> be refactored, then patching "mode" debugfs to work properly in that
>>> case. Only add otg.c/drd.c after "mode" debugfs file is stable, because
>>> then you know what needs to be taken into consideration.
>>>
>>> Just to be clear, I'm not saying we should *ONLY* get the debugfs
>>> interface for v4.12, I'm saying you should start with that and get that
>>> stable and working properly (make an infinite loop constantly changing
>>> modes and keep it running over the weekend) before you add support for
>>> OTG interrupts, which could come in the same series ;-)
>>>
>>
>> Just to clarify debugfs mode behaviour.
>>
>> Currently it is just changing PRTCAPDIR. What we need to do is that if
>> dr_mode == "otg", then we call dwc3_host/gadget_init/exit() accordingly as well.
>>
>> Does this make sense?
> 
> it does.
> 

OK. Below is a patch that allows us to use debugfs/mode to do the role switch.
Switching from device to host worked fine but I get the following error when
switching from host to device.

https://hastebin.com/liluqosewe.xml

cheers,
-roger

---
>From 50c49f18474b388d10533eb9f6d04f454fabf687 Mon Sep 17 00:00:00 2001
From: Roger Quadros <rogerq@...com>
Date: Fri, 31 Mar 2017 12:54:13 +0300
Subject: [PATCH] usb: dwc3: make role-switching work with debugfs/mode

If dr_mode == "otg", we start by default in PERIPHERAL mode.
Keep track of current role in "current_dr_role" whenever dwc3_set_mode()
is called.

When debugfs/mode is changed AND we're in dual-role mode,
handle the switch by stopping and starting the respective
host/gadget controllers.

Signed-off-by: Roger Quadros <rogerq@...com>
---
 drivers/usb/dwc3/core.c    | 38 +++++++++++++++++++++++------------
 drivers/usb/dwc3/core.h    |  2 ++
 drivers/usb/dwc3/debugfs.c | 49 +++++++++++++++++++++++++++++++++++++++-------
 3 files changed, 70 insertions(+), 19 deletions(-)

diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
index 369bab1..e2d36ba 100644
--- a/drivers/usb/dwc3/core.c
+++ b/drivers/usb/dwc3/core.c
@@ -108,6 +108,8 @@ void dwc3_set_mode(struct dwc3 *dwc, u32 mode)
 	reg &= ~(DWC3_GCTL_PRTCAPDIR(DWC3_GCTL_PRTCAP_OTG));
 	reg |= DWC3_GCTL_PRTCAPDIR(mode);
 	dwc3_writel(dwc->regs, DWC3_GCTL, reg);
+
+	dwc->current_dr_role = mode;
 }
 
 u32 dwc3_core_fifo_space(struct dwc3_ep *dep, u8 type)
@@ -862,13 +864,8 @@ static int dwc3_core_init_mode(struct dwc3 *dwc)
 		}
 		break;
 	case USB_DR_MODE_OTG:
-		ret = dwc3_host_init(dwc);
-		if (ret) {
-			if (ret != -EPROBE_DEFER)
-				dev_err(dev, "failed to initialize host\n");
-			return ret;
-		}
-
+		/* start in peripheral role by default */
+		dwc3_set_mode(dwc, DWC3_GCTL_PRTCAP_DEVICE);
 		ret = dwc3_gadget_init(dwc);
 		if (ret) {
 			if (ret != -EPROBE_DEFER)
@@ -894,8 +891,11 @@ static void dwc3_core_exit_mode(struct dwc3 *dwc)
 		dwc3_host_exit(dwc);
 		break;
 	case USB_DR_MODE_OTG:
-		dwc3_host_exit(dwc);
-		dwc3_gadget_exit(dwc);
+		/* role might have changed since start */
+		if (dwc->current_dr_role ==  DWC3_GCTL_PRTCAP_DEVICE)
+			dwc3_gadget_exit(dwc);
+		else if (dwc->current_dr_role == DWC3_GCTL_PRTCAP_HOST)
+			dwc3_host_exit(dwc);
 		break;
 	default:
 		/* do nothing */
@@ -1209,11 +1209,18 @@ static int dwc3_suspend_common(struct dwc3 *dwc)
 
 	switch (dwc->dr_mode) {
 	case USB_DR_MODE_PERIPHERAL:
-	case USB_DR_MODE_OTG:
 		spin_lock_irqsave(&dwc->lock, flags);
 		dwc3_gadget_suspend(dwc);
 		spin_unlock_irqrestore(&dwc->lock, flags);
 		break;
+	case USB_DR_MODE_OTG:
+		/* gadget might not be always present */
+		if (dwc->current_dr_role == DWC3_GCTL_PRTCAP_DEVICE) {
+			spin_lock_irqsave(&dwc->lock, flags);
+			dwc3_gadget_suspend(dwc);
+			spin_unlock_irqrestore(&dwc->lock, flags);
+		}
+		break;
 	case USB_DR_MODE_HOST:
 	default:
 		/* do nothing */
@@ -1236,11 +1243,18 @@ static int dwc3_resume_common(struct dwc3 *dwc)
 
 	switch (dwc->dr_mode) {
 	case USB_DR_MODE_PERIPHERAL:
-	case USB_DR_MODE_OTG:
 		spin_lock_irqsave(&dwc->lock, flags);
 		dwc3_gadget_resume(dwc);
 		spin_unlock_irqrestore(&dwc->lock, flags);
-		/* FALLTHROUGH */
+		break;
+	case USB_DR_MODE_OTG:
+		/* gadget might not be always present */
+		if (dwc->current_dr_role == DWC3_GCTL_PRTCAP_DEVICE) {
+			spin_lock_irqsave(&dwc->lock, flags);
+			dwc3_gadget_resume(dwc);
+			spin_unlock_irqrestore(&dwc->lock, flags);
+		}
+		break;
 	case USB_DR_MODE_HOST:
 	default:
 		/* do nothing */
diff --git a/drivers/usb/dwc3/core.h b/drivers/usb/dwc3/core.h
index 7ffdee5..f45ff44 100644
--- a/drivers/usb/dwc3/core.h
+++ b/drivers/usb/dwc3/core.h
@@ -785,6 +785,7 @@ struct dwc3_scratchpad_array {
  * @maximum_speed: maximum speed requested (mainly for testing purposes)
  * @revision: revision register contents
  * @dr_mode: requested mode of operation
+ * @current_dr_role: current role of operation when in dual-role mode
  * @hsphy_mode: UTMI phy mode, one of following:
  *		- USBPHY_INTERFACE_MODE_UTMI
  *		- USBPHY_INTERFACE_MODE_UTMIW
@@ -901,6 +902,7 @@ struct dwc3 {
 	size_t			regs_size;
 
 	enum usb_dr_mode	dr_mode;
+	u32			current_dr_role;
 	enum usb_phy_interface	hsphy_mode;
 
 	u32			fladj;
diff --git a/drivers/usb/dwc3/debugfs.c b/drivers/usb/dwc3/debugfs.c
index 31926dd..a101b14 100644
--- a/drivers/usb/dwc3/debugfs.c
+++ b/drivers/usb/dwc3/debugfs.c
@@ -327,19 +327,54 @@ static ssize_t dwc3_mode_write(struct file *file,
 		return -EFAULT;
 
 	if (!strncmp(buf, "host", 4))
-		mode |= DWC3_GCTL_PRTCAP_HOST;
+		mode = DWC3_GCTL_PRTCAP_HOST;
 
 	if (!strncmp(buf, "device", 6))
-		mode |= DWC3_GCTL_PRTCAP_DEVICE;
+		mode = DWC3_GCTL_PRTCAP_DEVICE;
 
 	if (!strncmp(buf, "otg", 3))
-		mode |= DWC3_GCTL_PRTCAP_OTG;
+		mode = DWC3_GCTL_PRTCAP_OTG;
 
-	if (mode) {
-		spin_lock_irqsave(&dwc->lock, flags);
-		dwc3_set_mode(dwc, mode);
-		spin_unlock_irqrestore(&dwc->lock, flags);
+	if (!mode)
+		return -EINVAL;
+
+	if (mode == dwc->current_dr_role)
+		goto exit;
+
+	/* prevent role switching if we're not dual-role */
+	if (dwc->dr_mode != USB_DR_MODE_OTG)
+		return -EINVAL;
+
+	/* stop old role */
+	if (dwc->current_dr_role == DWC3_GCTL_PRTCAP_HOST)
+	switch (dwc->current_dr_role) {
+	case DWC3_GCTL_PRTCAP_HOST:
+		dwc3_host_exit(dwc);
+		break;
+	case DWC3_GCTL_PRTCAP_DEVICE:
+		dwc3_gadget_exit(dwc);
+		break;
+	default:
+		break;
+	}
+
+	/* switch PRTCAP mode. updates current_dr_role */
+	spin_lock_irqsave(&dwc->lock, flags);
+	dwc3_set_mode(dwc, mode);
+	spin_unlock_irqrestore(&dwc->lock, flags);
+
+	/* start new role */
+	switch (dwc->current_dr_role) {
+	case DWC3_GCTL_PRTCAP_HOST:
+		dwc3_host_init(dwc);
+		break;
+	case DWC3_GCTL_PRTCAP_DEVICE:
+		dwc3_gadget_init(dwc);
+		break;
+	default:
+		break;
 	}
+exit:
 	return count;
 }
 
-- 
2.7.4

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