usb: dwc3: Allow disabling of metastability workaround

Some platforms (e.g. TI's DRA7 USB2 instance) have more trouble
with the metastability workaround as it supports only
a High-Speed PHY and the PHY can enter into an Erratic state [1]
when the controller is set in SuperSpeed mode as part of
the metastability workaround.

This causes upto 2 seconds delay in enumeration on DRA7's USB2
instance in gadget mode.

If these platforms can be better off without the workaround,
provide a device tree property to suggest that so the workaround
is avoided.

[1] Device mode enumeration trace showing PHY Erratic Error.
     irq/90-dwc3-969   [000] d...    52.323145: dwc3_event: event (00000901): Erratic Error [U0]
     irq/90-dwc3-969   [000] d...    52.560646: dwc3_event: event (00000901): Erratic Error [U0]
     irq/90-dwc3-969   [000] d...    52.798144: dwc3_event: event (00000901): Erratic Error [U0]

Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

diff --git a/Documentation/devicetree/bindings/usb/dwc3.txt b/Documentation/devicetree/bindings/usb/dwc3.txt
index 52fb410..44e8bab 100644 (file)
--- a/Documentation/devicetree/bindings/usb/dwc3.txt
+++ b/Documentation/devicetree/bindings/usb/dwc3.txt
@@ -47,6 +47,8 @@ Optional properties:
                        from P0 to P1/P2/P3 without delay.
  - snps,dis-tx-ipgap-linecheck-quirk: when set, disable u2mac linestate check
                        during HS transmit.
+ - snps,dis_metastability_quirk: when set, disable metastability workaround.
+                       CAUTION: use only if you are absolutely sure of it.
  - snps,is-utmi-l1-suspend: true when DWC3 asserts output signal
                        utmi_l1_suspend_n, false when asserts utmi_sleep_n
  - snps,hird-threshold: HIRD threshold

diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
index 0783250..c32d2b9 100644 (file)
--- a/drivers/usb/dwc3/core.c
+++ b/drivers/usb/dwc3/core.c
@@ -1062,6 +1062,9 @@ static void dwc3_get_properties(struct dwc3 *dwc)
        device_property_read_u32(dev, "snps,quirk-frame-length-adjustment",
                                 &dwc->fladj);
 
+       dwc->dis_metastability_quirk = device_property_read_bool(dev,
+                               "snps,dis_metastability_quirk");
+
        dwc->lpm_nyet_threshold = lpm_nyet_threshold;
        dwc->tx_de_emphasis = tx_de_emphasis;
 

diff --git a/drivers/usb/dwc3/core.h b/drivers/usb/dwc3/core.h
index be60d79..03c7aaa 100644 (file)
--- a/drivers/usb/dwc3/core.h
+++ b/drivers/usb/dwc3/core.h
@@ -856,6 +856,7 @@ struct dwc3_scratchpad_array {
  *     1       - -3.5dB de-emphasis
  *     2       - No de-emphasis
  *     3       - Reserved
+ * @dis_metastability_quirk: set to disable metastability quirk.
  * @imod_interval: set the interrupt moderation interval in 250ns
  *                 increments or 0 to disable.
  */
@@ -1008,6 +1009,8 @@ struct dwc3 {
        unsigned                tx_de_emphasis_quirk:1;
        unsigned                tx_de_emphasis:2;
 
+       unsigned                dis_metastability_quirk:1;
+
        u16                     imod_interval;
 };
 

diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index 981fd98..2168ba4 100644 (file)
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -2005,7 +2005,8 @@ static void dwc3_gadget_set_speed(struct usb_gadget *g,
         * STAR#9000525659: Clock Domain Crossing on DCTL in
         * USB 2.0 Mode
         */
-       if (dwc->revision < DWC3_REVISION_220A) {
+       if (dwc->revision < DWC3_REVISION_220A &&
+           !dwc->dis_metastability_quirk) {
                reg |= DWC3_DCFG_SUPERSPEED;
        } else {
                switch (speed) {
@@ -3224,7 +3225,8 @@ int dwc3_gadget_init(struct dwc3 *dwc)
         * is less than super speed because we don't have means, yet, to tell
         * composite.c that we are USB 2.0 + LPM ECN.
         */
-       if (dwc->revision < DWC3_REVISION_220A)
+       if (dwc->revision < DWC3_REVISION_220A &&
+           !dwc->dis_metastability_quirk)
                dev_info(dwc->dev, "changing max_speed on rev %08x\n",
                                dwc->revision);