[PATCH 5.4 65/86] xhci: tegra: Delay for disabling LFPS detector

Greg Kroah-Hartman
2021-01-26T16:39:17Z

From: JC Kuo <jckuo@nvidia.com>

commit da7e0c3c2909a3d9bf8acfe1db3cb213bd7febfb upstream.

Occasionally, we are seeing some SuperSpeed devices resumes right after
being directed to U3. This commits add 500us delay to ensure LFPS
detector is disabled before sending ACK to firmware.

[ 16.099363] tegra-xusb 70090000.usb: entering ELPG
[ 16.104343] tegra-xusb 70090000.usb: 2-1 isn't suspended: 0x0c001203
[ 16.114576] tegra-xusb 70090000.usb: not all ports suspended: -16
[ 16.120789] tegra-xusb 70090000.usb: entering ELPG failed

The register write passes through a few flop stages of 32KHz clock domain.
NVIDIA ASIC designer reviewed RTL and suggests 500us delay.

Cc: stable@vger.kernel.org
Signed-off-by: JC Kuo <jckuo@nvidia.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20210115161907.2875631-3-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/usb/host/xhci-tegra.c | 7 +++++++
1 file changed, 7 insertions(+)

--- a/drivers/usb/host/xhci-tegra.c
+++ b/drivers/usb/host/xhci-tegra.c
@@ -562,6 +562,13 @@ static void tegra_xusb_mbox_handle(struc
enable);
if (err < 0)
break;
+
+ /*
+ * wait 500us for LFPS detector to be disabled before
+ * sending ACK
+ */
+ if (!enable)
+ usleep_range(500, 1000);
}

if (err < 0) {