From f12524c9de802f3f76b889cd783116006675479a Mon Sep 17 00:00:00 2001
From: Greg Kroah-Hartman <gregkh@google.com>
Date: Wed, 6 Sep 2023 10:18:08 +0000
Subject: [PATCH] Revert "Revert "8250: add support for ASIX devices with a
 FIFO bug""

This reverts commit 599c0ebdb5ccd9afecc326c09c7a95aa8cb9dbcb which is
commit a82d62f708545d22859584e0e0620da8e3759bbc upstream.

It changes the serial port ABI, which Android cares about.  As the issue
isn't really a problem at all for any Android devices, just revert it
keeping the fix present for now, to preserve the abi.

Bug: 161946584
Change-Id: Ie9b3f9aa8e705c63680fb9556e579e6241589d74
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
---
 drivers/tty/serial/8250/8250.h      |  1 +
 drivers/tty/serial/8250/8250_pci.c  | 19 +++++++++++++++++++
 drivers/tty/serial/8250/8250_port.c | 11 ++++++++---
 include/linux/serial_8250.h         |  1 +
 4 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
index eeb7b43ebe53..1e8fe44a7099 100644
--- a/drivers/tty/serial/8250/8250.h
+++ b/drivers/tty/serial/8250/8250.h
@@ -91,6 +91,7 @@ struct serial8250_config {
 #define UART_BUG_TXEN	BIT(1)	/* UART has buggy TX IIR status */
 #define UART_BUG_NOMSR	BIT(2)	/* UART has buggy MSR status bits (Au1x00) */
 #define UART_BUG_THRE	BIT(3)	/* UART has buggy THRE reassertion */
+#define UART_BUG_PARITY	BIT(4)	/* UART mishandles parity if FIFO enabled */
 #define UART_BUG_TXRACE	BIT(5)	/* UART Tx fails to set remote DR */
 
 
diff --git a/drivers/tty/serial/8250/8250_pci.c b/drivers/tty/serial/8250/8250_pci.c
index 0ea89df6702f..cd27821f54ec 100644
--- a/drivers/tty/serial/8250/8250_pci.c
+++ b/drivers/tty/serial/8250/8250_pci.c
@@ -1252,6 +1252,14 @@ static int pci_oxsemi_tornado_setup(struct serial_private *priv,
 	return pci_default_setup(priv, board, up, idx);
 }
 
+static int pci_asix_setup(struct serial_private *priv,
+		  const struct pciserial_board *board,
+		  struct uart_8250_port *port, int idx)
+{
+	port->bugs |= UART_BUG_PARITY;
+	return pci_default_setup(priv, board, port, idx);
+}
+
 #define QPCR_TEST_FOR1		0x3F
 #define QPCR_TEST_GET1		0x00
 #define QPCR_TEST_FOR2		0x40
@@ -1967,6 +1975,7 @@ pci_moxa_setup(struct serial_private *priv,
 #define PCI_DEVICE_ID_WCH_CH355_4S	0x7173
 #define PCI_VENDOR_ID_AGESTAR		0x5372
 #define PCI_DEVICE_ID_AGESTAR_9375	0x6872
+#define PCI_VENDOR_ID_ASIX		0x9710
 #define PCI_DEVICE_ID_BROADCOM_TRUMANAGE 0x160a
 #define PCI_DEVICE_ID_AMCC_ADDIDATA_APCI7800 0x818e
 
@@ -2611,6 +2620,16 @@ static struct pci_serial_quirk pci_serial_quirks[] = {
 		.exit		= pci_wch_ch38x_exit,
 		.setup          = pci_wch_ch38x_setup,
 	},
+	/*
+	 * ASIX devices with FIFO bug
+	 */
+	{
+		.vendor		= PCI_VENDOR_ID_ASIX,
+		.device		= PCI_ANY_ID,
+		.subvendor	= PCI_ANY_ID,
+		.subdevice	= PCI_ANY_ID,
+		.setup		= pci_asix_setup,
+	},
 	/*
 	 * Broadcom TruManage (NetXtreme)
 	 */
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index acf578aa9930..b8e8a96c3eb6 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -2629,8 +2629,11 @@ static unsigned char serial8250_compute_lcr(struct uart_8250_port *up,
 
 	if (c_cflag & CSTOPB)
 		cval |= UART_LCR_STOP;
-	if (c_cflag & PARENB)
+	if (c_cflag & PARENB) {
 		cval |= UART_LCR_PARITY;
+		if (up->bugs & UART_BUG_PARITY)
+			up->fifo_bug = true;
+	}
 	if (!(c_cflag & PARODD))
 		cval |= UART_LCR_EPAR;
 	if (c_cflag & CMSPAR)
@@ -2791,7 +2794,8 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
 	up->lcr = cval;					/* Save computed LCR */
 
 	if (up->capabilities & UART_CAP_FIFO && port->fifosize > 1) {
-		if (baud < 2400 && !up->dma) {
+		/* NOTE: If fifo_bug is not set, a user can set RX_trigger. */
+		if ((baud < 2400 && !up->dma) || up->fifo_bug) {
 			up->fcr &= ~UART_FCR_TRIGGER_MASK;
 			up->fcr |= UART_FCR_TRIGGER_1;
 		}
@@ -3127,7 +3131,8 @@ static int do_set_rxtrig(struct tty_port *port, unsigned char bytes)
 	struct uart_8250_port *up = up_to_u8250p(uport);
 	int rxtrig;
 
-	if (!(up->capabilities & UART_CAP_FIFO) || uport->fifosize <= 1)
+	if (!(up->capabilities & UART_CAP_FIFO) || uport->fifosize <= 1 ||
+	    up->fifo_bug)
 		return -EINVAL;
 
 	rxtrig = bytes_to_fcr_rxtrig(up, bytes);
diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h
index 79b328861c5f..19376bee9667 100644
--- a/include/linux/serial_8250.h
+++ b/include/linux/serial_8250.h
@@ -98,6 +98,7 @@ struct uart_8250_port {
 	struct list_head	list;		/* ports on this IRQ */
 	u32			capabilities;	/* port capabilities */
 	unsigned short		bugs;		/* port bugs */
+	bool			fifo_bug;	/* min RX trigger if enabled */
 	unsigned int		tx_loadsz;	/* transmit fifo load size */
 	unsigned char		acr;
 	unsigned char		fcr;