[PATCH] usb: xhci: add support for performing fake doorbell

[PATCH] usb: xhci: add support for performing fake doorbell

[Rafał Miłecki]

From: Rafał Miłecki <rafal@milecki.pl>

Broadcom's Northstar XHCI controllers seem to need a special start
procedure to work correctly. There isn't any official documentation on
this, the problem is that controller doesn't detect any connected
devices with default setup. Moreover connecting USB device to controller
that doesn't run properly can cause SoC's watchdog issues.

A workaround that was successfully tested on multiple devices is to
perform a fake doorbell. This patch adds code for doing that and a DT
binding enabling it.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
---
 Documentation/devicetree/bindings/usb/usb-xhci.txt |  2 +
 drivers/usb/host/xhci-plat.c                       |  6 +++
 drivers/usb/host/xhci.c                            | 63 ++++++++++++++++++++--
 drivers/usb/host/xhci.h                            |  1 +
 4 files changed, 69 insertions(+), 3 deletions(-)

diff --git a/Documentation/devicetree/bindings/usb/usb-xhci.txt b/Documentation/devicetree/bindings/usb/usb-xhci.txt
index 966885c..ce01b7f 100644
--- a/Documentation/devicetree/bindings/usb/usb-xhci.txt
+++ b/Documentation/devicetree/bindings/usb/usb-xhci.txt
@@ -26,6 +26,8 @@ Required properties:
 Optional properties:
   - clocks: reference to a clock
   - usb3-lpm-capable: determines if platform is USB3 LPM capable
+  - usb3-fake-doorbell: determines if controller requires a fake doorbell when
+			starting it
 
 Example:
 	usb@f0931000 {
diff --git a/drivers/usb/host/xhci-plat.c b/drivers/usb/host/xhci-plat.c
index ed56bf9..c26dc77 100644
--- a/drivers/usb/host/xhci-plat.c
+++ b/drivers/usb/host/xhci-plat.c
@@ -56,12 +56,18 @@ static int xhci_priv_init_quirk(struct usb_hcd *hcd)
 
 static void xhci_plat_quirks(struct device *dev, struct xhci_hcd *xhci)
 {
+	struct platform_device	*pdev = to_platform_device(dev);
+	struct device_node	*node = pdev->dev.of_node;
+
 	/*
 	 * As of now platform drivers don't provide MSI support so we ensure
 	 * here that the generic code does not try to make a pci_dev from our
 	 * dev struct in order to setup MSI
 	 */
 	xhci->quirks |= XHCI_PLAT;
+
+	if (node && of_property_read_bool(node, "usb3-fake-doorbell"))
+		xhci->quirks |= XHCI_FAKE_DOORBELL;
 }
 
 /* called during probe() after chip reset completes */
diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
index 1a4ca02..c77035e9b 100644
--- a/drivers/usb/host/xhci.c
+++ b/drivers/usb/host/xhci.c
@@ -153,6 +153,49 @@ static int xhci_start(struct xhci_hcd *xhci)
 	return ret;
 }
 
+/**
+ * xhci_fake_doorbell - Perform a fake doorbell on a specified slot
+ *
+ * Some controllers require a fake doorbell to start correctly. Without that
+ * they simply don't detect any devices.
+ */
+static int xhci_fake_doorbell(struct xhci_hcd *xhci, int slot_id)
+{
+	u32 temp;
+
+	/* Alloc a virt device for that slot */
+	if (!xhci_alloc_virt_device(xhci, slot_id, NULL, GFP_NOIO)) {
+		xhci_warn(xhci, "Could not allocate xHCI USB device data structures\n");
+		return -ENOMEM;
+	}
+
+	/* Ring fake doorbell for slot_id ep 0 */
+	xhci_ring_ep_doorbell(xhci, slot_id, 0, 0);
+	usleep_range(1000, 1500);
+
+	/* Read the status to check if HSE is set or not */
+	temp = readl(&xhci->op_regs->status);
+
+	/* Clear HSE if set */
+	if (temp & STS_FATAL) {
+		xhci_dbg(xhci, "HSE problem detected, status: 0x%08x\n", temp);
+		temp &= ~0x1fff;
+		temp |= STS_FATAL;
+		writel(temp, &xhci->op_regs->status);
+		usleep_range(1000, 1500);
+		readl(&xhci->op_regs->status);
+	}
+
+	/* Free virt device */
+	xhci_free_virt_device(xhci, slot_id);
+
+	/* We're done if controller is already running */
+	if (readl(&xhci->op_regs->command) & CMD_RUN)
+		return 0;
+
+	return xhci_start(xhci);
+}
+
 /*
  * Reset a halted HC.
  *
@@ -565,10 +608,20 @@ int xhci_init(struct usb_hcd *hcd)
 
 static int xhci_run_finished(struct xhci_hcd *xhci)
 {
-	if (xhci_start(xhci)) {
-		xhci_halt(xhci);
-		return -ENODEV;
+	int err;
+
+	err = xhci_start(xhci);
+	if (err) {
+		err = -ENODEV;
+		goto err_halt;
+	}
+
+	if (xhci->quirks & XHCI_FAKE_DOORBELL) {
+		err = xhci_fake_doorbell(xhci, 1);
+		if (err)
+			goto err_halt;
 	}
+
 	xhci->shared_hcd->state = HC_STATE_RUNNING;
 	xhci->cmd_ring_state = CMD_RING_STATE_RUNNING;
 
@@ -578,6 +631,10 @@ static int xhci_run_finished(struct xhci_hcd *xhci)
 	xhci_dbg_trace(xhci, trace_xhci_dbg_init,
 			"Finished xhci_run for USB3 roothub");
 	return 0;
+
+err_halt:
+	xhci_halt(xhci);
+	return err;
 }
 
 /*
diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
index b2c1dc5..52d7498 100644
--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h
@@ -1653,6 +1653,7 @@ struct xhci_hcd {
 #define XHCI_MTK_HOST		(1 << 21)
 #define XHCI_SSIC_PORT_UNUSED	(1 << 22)
 #define XHCI_NO_64BIT_SUPPORT	(1 << 23)
+#define XHCI_FAKE_DOORBELL	(1 << 24)
 	unsigned int		num_active_eps;
 	unsigned int		limit_active_eps;
 	/* There are two roothubs to keep track of bus suspend info for */
-- 
2.9.3

Re: [PATCH] usb: xhci: add support for performing fake doorbell

[Rob Herring]

On Sat, Oct 01, 2016 at 11:58:10PM +0200, Rafał Miłecki wrote:
> From: Rafał Miłecki <rafal-g1n6cQUeyibVItvQsEIGlw@public.gmane.org>
> 
> Broadcom's Northstar XHCI controllers seem to need a special start
> procedure to work correctly. There isn't any official documentation on
> this, the problem is that controller doesn't detect any connected
> devices with default setup. Moreover connecting USB device to controller
> that doesn't run properly can cause SoC's watchdog issues.
> 
> A workaround that was successfully tested on multiple devices is to
> perform a fake doorbell. This patch adds code for doing that and a DT
> binding enabling it.
> 
> Signed-off-by: Rafał Miłecki <rafal-g1n6cQUeyibVItvQsEIGlw@public.gmane.org>
> ---
>  Documentation/devicetree/bindings/usb/usb-xhci.txt |  2 +
>  drivers/usb/host/xhci-plat.c                       |  6 +++
>  drivers/usb/host/xhci.c                            | 63 ++++++++++++++++++++--
>  drivers/usb/host/xhci.h                            |  1 +
>  4 files changed, 69 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/usb/usb-xhci.txt b/Documentation/devicetree/bindings/usb/usb-xhci.txt
> index 966885c..ce01b7f 100644
> --- a/Documentation/devicetree/bindings/usb/usb-xhci.txt
> +++ b/Documentation/devicetree/bindings/usb/usb-xhci.txt
> @@ -26,6 +26,8 @@ Required properties:
>  Optional properties:
>    - clocks: reference to a clock
>    - usb3-lpm-capable: determines if platform is USB3 LPM capable
> +  - usb3-fake-doorbell: determines if controller requires a fake doorbell when
> +			starting it

You should use Northstar XHCI compatible string to enable this. Then the 
DT doesn't need updating.

Rob
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[PATCH V2] usb: xhci: add support for performing fake doorbell

[Rafał Miłecki]

From: Rafał Miłecki <rafal-g1n6cQUeyibVItvQsEIGlw@public.gmane.org>

Broadcom's Northstar XHCI controllers seem to need a special start
procedure to work correctly. There isn't any official documentation of
this, the problem is that controller doesn't detect any connected
devices with default setup. Moreover connecting USB device to controller
that doesn't run properly can cause SoC's watchdog issues.

A workaround that was successfully tested on multiple devices is to
perform a fake doorbell. This patch adds code for doing this and enables
it on BCM4708 family.

Signed-off-by: Rafał Miłecki <rafal-g1n6cQUeyibVItvQsEIGlw@public.gmane.org>
---
V2: Enable quirk for brcm,bcm4708 machines instead of adding separated binding
    for it. Thanks Rob for your comment on this.
---
 drivers/usb/host/xhci-plat.c |  6 +++++
 drivers/usb/host/xhci.c      | 63 +++++++++++++++++++++++++++++++++++++++++---
 drivers/usb/host/xhci.h      |  1 +
 3 files changed, 67 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/host/xhci-plat.c b/drivers/usb/host/xhci-plat.c
index ed56bf9..b01a3be 100644
--- a/drivers/usb/host/xhci-plat.c
+++ b/drivers/usb/host/xhci-plat.c
@@ -56,12 +56,18 @@ static int xhci_priv_init_quirk(struct usb_hcd *hcd)
 
 static void xhci_plat_quirks(struct device *dev, struct xhci_hcd *xhci)
 {
+	struct platform_device	*pdev = to_platform_device(dev);
+	struct device_node	*node = pdev->dev.of_node;
+
 	/*
 	 * As of now platform drivers don't provide MSI support so we ensure
 	 * here that the generic code does not try to make a pci_dev from our
 	 * dev struct in order to setup MSI
 	 */
 	xhci->quirks |= XHCI_PLAT;
+
+	if (node && of_machine_is_compatible("brcm,bcm4708"))
+		xhci->quirks |= XHCI_FAKE_DOORBELL;
 }
 
 /* called during probe() after chip reset completes */
diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
index 1a4ca02..c77035e9b 100644
--- a/drivers/usb/host/xhci.c
+++ b/drivers/usb/host/xhci.c
@@ -153,6 +153,49 @@ static int xhci_start(struct xhci_hcd *xhci)
 	return ret;
 }
 
+/**
+ * xhci_fake_doorbell - Perform a fake doorbell on a specified slot
+ *
+ * Some controllers require a fake doorbell to start correctly. Without that
+ * they simply don't detect any devices.
+ */
+static int xhci_fake_doorbell(struct xhci_hcd *xhci, int slot_id)
+{
+	u32 temp;
+
+	/* Alloc a virt device for that slot */
+	if (!xhci_alloc_virt_device(xhci, slot_id, NULL, GFP_NOIO)) {
+		xhci_warn(xhci, "Could not allocate xHCI USB device data structures\n");
+		return -ENOMEM;
+	}
+
+	/* Ring fake doorbell for slot_id ep 0 */
+	xhci_ring_ep_doorbell(xhci, slot_id, 0, 0);
+	usleep_range(1000, 1500);
+
+	/* Read the status to check if HSE is set or not */
+	temp = readl(&xhci->op_regs->status);
+
+	/* Clear HSE if set */
+	if (temp & STS_FATAL) {
+		xhci_dbg(xhci, "HSE problem detected, status: 0x%08x\n", temp);
+		temp &= ~0x1fff;
+		temp |= STS_FATAL;
+		writel(temp, &xhci->op_regs->status);
+		usleep_range(1000, 1500);
+		readl(&xhci->op_regs->status);
+	}
+
+	/* Free virt device */
+	xhci_free_virt_device(xhci, slot_id);
+
+	/* We're done if controller is already running */
+	if (readl(&xhci->op_regs->command) & CMD_RUN)
+		return 0;
+
+	return xhci_start(xhci);
+}
+
 /*
  * Reset a halted HC.
  *
@@ -565,10 +608,20 @@ int xhci_init(struct usb_hcd *hcd)
 
 static int xhci_run_finished(struct xhci_hcd *xhci)
 {
-	if (xhci_start(xhci)) {
-		xhci_halt(xhci);
-		return -ENODEV;
+	int err;
+
+	err = xhci_start(xhci);
+	if (err) {
+		err = -ENODEV;
+		goto err_halt;
+	}
+
+	if (xhci->quirks & XHCI_FAKE_DOORBELL) {
+		err = xhci_fake_doorbell(xhci, 1);
+		if (err)
+			goto err_halt;
 	}
+
 	xhci->shared_hcd->state = HC_STATE_RUNNING;
 	xhci->cmd_ring_state = CMD_RING_STATE_RUNNING;
 
@@ -578,6 +631,10 @@ static int xhci_run_finished(struct xhci_hcd *xhci)
 	xhci_dbg_trace(xhci, trace_xhci_dbg_init,
 			"Finished xhci_run for USB3 roothub");
 	return 0;
+
+err_halt:
+	xhci_halt(xhci);
+	return err;
 }
 
 /*
diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
index b2c1dc5..52d7498 100644
--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h
@@ -1653,6 +1653,7 @@ struct xhci_hcd {
 #define XHCI_MTK_HOST		(1 << 21)
 #define XHCI_SSIC_PORT_UNUSED	(1 << 22)
 #define XHCI_NO_64BIT_SUPPORT	(1 << 23)
+#define XHCI_FAKE_DOORBELL	(1 << 24)
 	unsigned int		num_active_eps;
 	unsigned int		limit_active_eps;
 	/* There are two roothubs to keep track of bus suspend info for */
-- 
2.9.3

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Re: [PATCH V2] usb: xhci: add support for performing fake doorbell

[Hauke Mehrtens]

On 10/17/2016 10:30 PM, Rafał Miłecki wrote:
> From: Rafał Miłecki <rafal@milecki.pl>
> 
> Broadcom's Northstar XHCI controllers seem to need a special start
> procedure to work correctly. There isn't any official documentation of
> this, the problem is that controller doesn't detect any connected
> devices with default setup. Moreover connecting USB device to controller
> that doesn't run properly can cause SoC's watchdog issues.
> 
> A workaround that was successfully tested on multiple devices is to
> perform a fake doorbell. This patch adds code for doing this and enables
> it on BCM4708 family.
> 
> Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
> ---
> V2: Enable quirk for brcm,bcm4708 machines instead of adding separated binding
>     for it. Thanks Rob for your comment on this.
> ---
>  drivers/usb/host/xhci-plat.c |  6 +++++
>  drivers/usb/host/xhci.c      | 63 +++++++++++++++++++++++++++++++++++++++++---
>  drivers/usb/host/xhci.h      |  1 +
>  3 files changed, 67 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/usb/host/xhci-plat.c b/drivers/usb/host/xhci-plat.c
> index ed56bf9..b01a3be 100644
> --- a/drivers/usb/host/xhci-plat.c
> +++ b/drivers/usb/host/xhci-plat.c
> @@ -56,12 +56,18 @@ static int xhci_priv_init_quirk(struct usb_hcd *hcd)
>  
>  static void xhci_plat_quirks(struct device *dev, struct xhci_hcd *xhci)
>  {
> +	struct platform_device	*pdev = to_platform_device(dev);
> +	struct device_node	*node = pdev->dev.of_node;
> +
>  	/*
>  	 * As of now platform drivers don't provide MSI support so we ensure
>  	 * here that the generic code does not try to make a pci_dev from our
>  	 * dev struct in order to setup MSI
>  	 */
>  	xhci->quirks |= XHCI_PLAT;
> +
> +	if (node && of_machine_is_compatible("brcm,bcm4708"))
> +		xhci->quirks |= XHCI_FAKE_DOORBELL;

Are you sure only the bcm4708 and similar SoCs are affected? Having here
a list with 3 or more checks would looks strange. I prefer your first patch.

@Florian do you know if other Broadcom SoC are affected by this problem
or are only Northstar SoCs affected?

Hauke

Re: [PATCH V2] usb: xhci: add support for performing fake doorbell

[Rafał Miłecki]

On 17 October 2016 at 23:10, Hauke Mehrtens <hauke-5/S+JYg5SzeELgA04lAiVw@public.gmane.org> wrote:
> On 10/17/2016 10:30 PM, Rafał Miłecki wrote:
>> From: Rafał Miłecki <rafal-g1n6cQUeyibVItvQsEIGlw@public.gmane.org>
>>
>> Broadcom's Northstar XHCI controllers seem to need a special start
>> procedure to work correctly. There isn't any official documentation of
>> this, the problem is that controller doesn't detect any connected
>> devices with default setup. Moreover connecting USB device to controller
>> that doesn't run properly can cause SoC's watchdog issues.
>>
>> A workaround that was successfully tested on multiple devices is to
>> perform a fake doorbell. This patch adds code for doing this and enables
>> it on BCM4708 family.
>>
>> Signed-off-by: Rafał Miłecki <rafal-g1n6cQUeyibVItvQsEIGlw@public.gmane.org>
>> ---
>> V2: Enable quirk for brcm,bcm4708 machines instead of adding separated binding
>>     for it. Thanks Rob for your comment on this.
>> ---
>>  drivers/usb/host/xhci-plat.c |  6 +++++
>>  drivers/usb/host/xhci.c      | 63 +++++++++++++++++++++++++++++++++++++++++---
>>  drivers/usb/host/xhci.h      |  1 +
>>  3 files changed, 67 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/usb/host/xhci-plat.c b/drivers/usb/host/xhci-plat.c
>> index ed56bf9..b01a3be 100644
>> --- a/drivers/usb/host/xhci-plat.c
>> +++ b/drivers/usb/host/xhci-plat.c
>> @@ -56,12 +56,18 @@ static int xhci_priv_init_quirk(struct usb_hcd *hcd)
>>
>>  static void xhci_plat_quirks(struct device *dev, struct xhci_hcd *xhci)
>>  {
>> +     struct platform_device  *pdev = to_platform_device(dev);
>> +     struct device_node      *node = pdev->dev.of_node;
>> +
>>       /*
>>        * As of now platform drivers don't provide MSI support so we ensure
>>        * here that the generic code does not try to make a pci_dev from our
>>        * dev struct in order to setup MSI
>>        */
>>       xhci->quirks |= XHCI_PLAT;
>> +
>> +     if (node && of_machine_is_compatible("brcm,bcm4708"))
>> +             xhci->quirks |= XHCI_FAKE_DOORBELL;
>
> Are you sure only the bcm4708 and similar SoCs are affected? Having here
> a list with 3 or more checks would looks strange. I prefer your first patch.
>
> @Florian do you know if other Broadcom SoC are affected by this problem
> or are only Northstar SoCs affected?

I also believed usb3-fake-doorbell property looks nicer, but then just
followed Rob's suggestion.

I don't know about Northstar Plus or Northstar 2, I just know it's not
needed for BCM53573.

-- 
Rafał
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Re: [PATCH V2] usb: xhci: add support for performing fake doorbell

[Rafał Miłecki]

Hi Mathias,

On 17 October 2016 at 22:30, Rafał Miłecki <zajec5@gmail.com> wrote:
> From: Rafał Miłecki <rafal@milecki.pl>
>
> Broadcom's Northstar XHCI controllers seem to need a special start
> procedure to work correctly. There isn't any official documentation of
> this, the problem is that controller doesn't detect any connected
> devices with default setup. Moreover connecting USB device to controller
> that doesn't run properly can cause SoC's watchdog issues.
>
> A workaround that was successfully tested on multiple devices is to
> perform a fake doorbell. This patch adds code for doing this and enables
> it on BCM4708 family.
>
> Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
> ---
> V2: Enable quirk for brcm,bcm4708 machines instead of adding separated binding
>     for it. Thanks Rob for your comment on this.

Do you think you can pick & push this one? V2 follows Rob's suggestion
and he has some DT knowledge for sure, so I guess it should be OK.

Re: [PATCH V2] usb: xhci: add support for performing fake doorbell

[Mathias Nyman]

On 21.11.2016 09:57, Rafał Miłecki wrote:
> Hi Mathias,
>
> On 17 October 2016 at 22:30, Rafał Miłecki <zajec5@gmail.com> wrote:
>> From: Rafał Miłecki <rafal@milecki.pl>
>>
>> Broadcom's Northstar XHCI controllers seem to need a special start
>> procedure to work correctly. There isn't any official documentation of
>> this, the problem is that controller doesn't detect any connected
>> devices with default setup. Moreover connecting USB device to controller
>> that doesn't run properly can cause SoC's watchdog issues.
>>
>> A workaround that was successfully tested on multiple devices is to
>> perform a fake doorbell. This patch adds code for doing this and enables
>> it on BCM4708 family.
>>
>> Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
>> ---
>> V2: Enable quirk for brcm,bcm4708 machines instead of adding separated binding
>>      for it. Thanks Rob for your comment on this.
>
> Do you think you can pick & push this one? V2 follows Rob's suggestion
> and he has some DT knowledge for sure, so I guess it should be OK.
> --

Is there some more background information on this?

I don't have any contacts to Broadcom myself, adding the BMC Kernel Feedback list to CC.
Maybe someone over there has an errata, documentation or just general feedback.

How was this workaround even figured out? ringing the doorbell for the first
device doesn't seem like something found by trial and error,  especially when
xhci specs state that:

"Software shall not write the Doorbell of an endpoint until after it has issued a
Configure Endpoint Command for the endpoint and received a successful Command
Completion Event."

The whole workaround is a bit intrusive, allocating a fake device, ring a doorbell for a
fake device in the wrong state, clearing off HSE (host system error) which should only be set
when things really go bad, some random usleeps, and possible calling xhci_start() twice.

I can't take this as is without some more info.

-Mathias

Re: [PATCH V2] usb: xhci: add support for performing fake doorbell

[Rafał Miłecki]

On 21 November 2016 at 16:31, Mathias Nyman
<mathias.nyman@linux.intel.com> wrote:
> On 21.11.2016 09:57, Rafał Miłecki wrote:
>>
>> Hi Mathias,
>>
>> On 17 October 2016 at 22:30, Rafał Miłecki <zajec5@gmail.com> wrote:
>>>
>>> From: Rafał Miłecki <rafal@milecki.pl>
>>>
>>> Broadcom's Northstar XHCI controllers seem to need a special start
>>> procedure to work correctly. There isn't any official documentation of
>>> this, the problem is that controller doesn't detect any connected
>>> devices with default setup. Moreover connecting USB device to controller
>>> that doesn't run properly can cause SoC's watchdog issues.
>>>
>>> A workaround that was successfully tested on multiple devices is to
>>> perform a fake doorbell. This patch adds code for doing this and enables
>>> it on BCM4708 family.
>>>
>>> Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
>>> ---
>>> V2: Enable quirk for brcm,bcm4708 machines instead of adding separated
>>> binding
>>>      for it. Thanks Rob for your comment on this.
>>
>>
>> Do you think you can pick & push this one? V2 follows Rob's suggestion
>> and he has some DT knowledge for sure, so I guess it should be OK.
>> --
>
>
> Is there some more background information on this?
>
> I don't have any contacts to Broadcom myself, adding the BMC Kernel Feedback
> list to CC.
> Maybe someone over there has an errata, documentation or just general
> feedback.
>
> How was this workaround even figured out? ringing the doorbell for the first
> device doesn't seem like something found by trial and error,  especially
> when
> xhci specs state that:
>
> "Software shall not write the Doorbell of an endpoint until after it has
> issued a
> Configure Endpoint Command for the endpoint and received a successful
> Command
> Completion Event."
>
> The whole workaround is a bit intrusive, allocating a fake device, ring a
> doorbell for a
> fake device in the wrong state, clearing off HSE (host system error) which
> should only be set
> when things really go bad, some random usleeps, and possible calling
> xhci_start() twice.
>
> I can't take this as is without some more info.

Hi (ping) Broadcom guys, could you help us with this USB workaround, please?

-- 
Rafał

Re: [PATCH V2] usb: xhci: add support for performing fake doorbell

[Jon Mason]

On Mon, Jan 16, 2017 at 2:32 AM, Rafał Miłecki <zajec5-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> On 21 November 2016 at 16:31, Mathias Nyman
> <mathias.nyman-VuQAYsv1563Yd54FQh9/CA@public.gmane.org> wrote:
>> On 21.11.2016 09:57, Rafał Miłecki wrote:
>>>
>>> Hi Mathias,
>>>
>>> On 17 October 2016 at 22:30, Rafał Miłecki <zajec5-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>>>>
>>>> From: Rafał Miłecki <rafal-g1n6cQUeyibVItvQsEIGlw@public.gmane.org>
>>>>
>>>> Broadcom's Northstar XHCI controllers seem to need a special start
>>>> procedure to work correctly. There isn't any official documentation of
>>>> this, the problem is that controller doesn't detect any connected
>>>> devices with default setup. Moreover connecting USB device to controller
>>>> that doesn't run properly can cause SoC's watchdog issues.
>>>>
>>>> A workaround that was successfully tested on multiple devices is to
>>>> perform a fake doorbell. This patch adds code for doing this and enables
>>>> it on BCM4708 family.
>>>>
>>>> Signed-off-by: Rafał Miłecki <rafal-g1n6cQUeyibVItvQsEIGlw@public.gmane.org>
>>>> ---
>>>> V2: Enable quirk for brcm,bcm4708 machines instead of adding separated
>>>> binding
>>>>      for it. Thanks Rob for your comment on this.
>>>
>>>
>>> Do you think you can pick & push this one? V2 follows Rob's suggestion
>>> and he has some DT knowledge for sure, so I guess it should be OK.
>>> --
>>
>>
>> Is there some more background information on this?
>>
>> I don't have any contacts to Broadcom myself, adding the BMC Kernel Feedback
>> list to CC.
>> Maybe someone over there has an errata, documentation or just general
>> feedback.
>>
>> How was this workaround even figured out? ringing the doorbell for the first
>> device doesn't seem like something found by trial and error,  especially
>> when
>> xhci specs state that:
>>
>> "Software shall not write the Doorbell of an endpoint until after it has
>> issued a
>> Configure Endpoint Command for the endpoint and received a successful
>> Command
>> Completion Event."
>>
>> The whole workaround is a bit intrusive, allocating a fake device, ring a
>> doorbell for a
>> fake device in the wrong state, clearing off HSE (host system error) which
>> should only be set
>> when things really go bad, some random usleeps, and possible calling
>> xhci_start() twice.
>>
>> I can't take this as is without some more info.
>
> Hi (ping) Broadcom guys, could you help us with this USB workaround, please?

Investigating internally.  I'll let you know if I can find anything.

Thanks,
Jon

>
> --
> Rafał
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