[PATCH 2/2] xhci: tegra: Delay for disabling LFPS detector

From: Mathias Nyman <mathias.nyman@linux.intel.com>
To: <gregkh@linuxfoundation.org>
Cc: <linux-usb@vger.kernel.org>, JC Kuo <jckuo@nvidia.com>,
	stable@vger.kernel.org,
	Mathias Nyman <mathias.nyman@linux.intel.com>
Subject: [PATCH 2/2] xhci: tegra: Delay for disabling LFPS detector
Date: Fri, 15 Jan 2021 18:19:07 +0200	[thread overview]
Message-ID: <20210115161907.2875631-3-mathias.nyman@linux.intel.com> (raw)
In-Reply-To: <20210115161907.2875631-1-mathias.nyman@linux.intel.com>

From: JC Kuo <jckuo@nvidia.com>

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

diff --git a/drivers/usb/host/xhci-tegra.c b/drivers/usb/host/xhci-tegra.c
index 934be1686352..50bb91b6a4b8 100644
--- a/drivers/usb/host/xhci-tegra.c
+++ b/drivers/usb/host/xhci-tegra.c
@@ -623,6 +623,13 @@ static void tegra_xusb_mbox_handle(struct tegra_xusb *tegra,
 								     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) {
-- 
2.25.1

