Revert "Revert "8250: add support for ASIX devices with a FIFO bug""

This reverts commit 5f4a1111ad which is
commit a82d62f708 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

@@ -87,6 +87,7 @@ struct serial8250_config {
 #define UART_BUG_TXEN	(1 << 1)	/* UART has buggy TX IIR status */
 #define UART_BUG_NOMSR	(1 << 2)	/* UART has buggy MSR status bits (Au1x00) */
 #define UART_BUG_THRE	(1 << 3)	/* UART has buggy THRE reassertion */
+#define UART_BUG_PARITY	(1 << 4)	/* UART mishandles parity if FIFO enabled */
 #define UART_BUG_TXRACE	(1 << 5)	/* UART Tx fails to set remote DR */
 
 

drivers/tty/serial/8250/8250_pci.c

@@ -1044,6 +1044,14 @@ static int pci_oxsemi_tornado_init(struct pci_dev *dev)
 	return number_uarts;
 }
 
+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);
+}
+
 /* Quatech devices have their own extra interface features */
 
 struct quatech_feature {
@@ -1866,6 +1874,7 @@ 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
 
@@ -2675,6 +2684,16 @@ static struct pci_serial_quirk pci_serial_quirks[] __refdata = {
 		.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)
 	 */

drivers/tty/serial/8250/8250_port.c

@@ -2574,8 +2574,11 @@ 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;
 #ifdef CMSPAR
@@ -2738,7 +2741,8 @@ 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;
 		}
@@ -3074,7 +3078,8 @@ 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);

include/linux/serial_8250.h

@@ -97,6 +97,7 @@ 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;