[v13,tty-next,2/4] serial: 8250_pci1xxxx: Add driver for quad-uart support

  pci1xxxx is a PCIe switch with a multi-function endpoint on one of
its downstream ports. Quad-uart is one of the functions in the
multi-function endpoint. This driver loads for the quad-uart and
enumerates single or multiple instances of uart based on the PCIe
subsystem device ID.

Co-developed-by: Tharun Kumar P <tharunkumar.pasumarthi@microchip.com>
Signed-off-by: Tharun Kumar P <tharunkumar.pasumarthi@microchip.com>
Signed-off-by: Kumaravel Thiagarajan <kumaravel.thiagarajan@microchip.com>
---
Changes in v13:
- No Change

Changes in v12:
- No Change

Changes in v11:
- Code rebased to linux-next master branch as suggested by Greg

Changes in v10:
- Added spaces to improve readability
- Used macro for PORT_OFFSET
- Used pci_free_irq_vectors API

Changes in v9:
- Reshuffled code logically
- Modified datatype of few variables
- Removed un-necessary else
- Used PCI_VDEVICE()

Changes in v8:
- Requested only required number of interrupt vectors in
  pci_alloc_irq_vectors
  API based on sub-device id

Changes in v7:
- Used appropriate error codes
- Moved logical_to_physical_port_idx array to a function

Changes in v6:
- Removed un-necessary paranthesis
- Used array and removed switch cases to reduce complexity
- Handled failure case of pcim_iomap

Changes in v5:
- Used tabs instead of spaces in MACRO definitions for readability
- Removed assignments that are not required
- Removed redundant blank lines

Changes in v4:
- Renamed pci_setup_port to serial8250_pci_setup_port
- Added Copyright information to 8250_pcilib.c

Changes in v3:
- Used NSEC_PER_SEC, HZ_PER_MHZ, FIELD_PREP, FIELD_GET MACROs wherever
  necessary
- Handled failure case of serial8250_register_8250_port properly
- Moved pci_setup_port to 8250_pcilib.c

Changes in v2:
- Use only the 62.5 MHz for baud clock.
- Define custom implementation for get_divisor and set_divisor.
- Use BOTHER instead of UPF_SPD_CUST for non standard baud rates
  (untested).
- Correct indentation in clock divisor computation.
- Remove unnecessary call to pci_save_state in probe function.
- Fix null pointer dereference in probe function.
- Move pci1xxxx_rs485_config to a separate patch.
- Depends on SERIAL_8250_PCI & default to SERIAL_8250.
- Change PORT_MCHP16550A to 100 from 124.
---
 MAINTAINERS                             |   7 +
 drivers/tty/serial/8250/8250_pci1xxxx.c | 329 ++++++++++++++++++++++++
 drivers/tty/serial/8250/8250_port.c     |   8 +
 drivers/tty/serial/8250/Kconfig         |  11 +
 drivers/tty/serial/8250/Makefile        |   1 +
 include/uapi/linux/serial_core.h        |   3 +
 6 files changed, 359 insertions(+)
 create mode 100644 drivers/tty/serial/8250/8250_pci1xxxx.c
  

On Tue, Feb 07, 2023 at 10:18:12PM +0530, Kumaravel Thiagarajan wrote:
> pci1xxxx is a PCIe switch with a multi-function endpoint on one of
> its downstream ports. Quad-uart is one of the functions in the
> multi-function endpoint. This driver loads for the quad-uart and
> enumerates single or multiple instances of uart based on the PCIe
> subsystem device ID.

I think it's good enough now and if anything we may fix in the followups.
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

> Co-developed-by: Tharun Kumar P <tharunkumar.pasumarthi@microchip.com>
> Signed-off-by: Tharun Kumar P <tharunkumar.pasumarthi@microchip.com>
> Signed-off-by: Kumaravel Thiagarajan <kumaravel.thiagarajan@microchip.com>
> ---
> Changes in v13:
> - No Change
> 
> Changes in v12:
> - No Change
> 
> Changes in v11:
> - Code rebased to linux-next master branch as suggested by Greg
> 
> Changes in v10:
> - Added spaces to improve readability
> - Used macro for PORT_OFFSET
> - Used pci_free_irq_vectors API
> 
> Changes in v9:
> - Reshuffled code logically
> - Modified datatype of few variables
> - Removed un-necessary else
> - Used PCI_VDEVICE()
> 
> Changes in v8:
> - Requested only required number of interrupt vectors in
>   pci_alloc_irq_vectors
>   API based on sub-device id
> 
> Changes in v7:
> - Used appropriate error codes
> - Moved logical_to_physical_port_idx array to a function
> 
> Changes in v6:
> - Removed un-necessary paranthesis
> - Used array and removed switch cases to reduce complexity
> - Handled failure case of pcim_iomap
> 
> Changes in v5:
> - Used tabs instead of spaces in MACRO definitions for readability
> - Removed assignments that are not required
> - Removed redundant blank lines
> 
> Changes in v4:
> - Renamed pci_setup_port to serial8250_pci_setup_port
> - Added Copyright information to 8250_pcilib.c
> 
> Changes in v3:
> - Used NSEC_PER_SEC, HZ_PER_MHZ, FIELD_PREP, FIELD_GET MACROs wherever
>   necessary
> - Handled failure case of serial8250_register_8250_port properly
> - Moved pci_setup_port to 8250_pcilib.c
> 
> Changes in v2:
> - Use only the 62.5 MHz for baud clock.
> - Define custom implementation for get_divisor and set_divisor.
> - Use BOTHER instead of UPF_SPD_CUST for non standard baud rates
>   (untested).
> - Correct indentation in clock divisor computation.
> - Remove unnecessary call to pci_save_state in probe function.
> - Fix null pointer dereference in probe function.
> - Move pci1xxxx_rs485_config to a separate patch.
> - Depends on SERIAL_8250_PCI & default to SERIAL_8250.
> - Change PORT_MCHP16550A to 100 from 124.
> ---
>  MAINTAINERS                             |   7 +
>  drivers/tty/serial/8250/8250_pci1xxxx.c | 329 ++++++++++++++++++++++++
>  drivers/tty/serial/8250/8250_port.c     |   8 +
>  drivers/tty/serial/8250/Kconfig         |  11 +
>  drivers/tty/serial/8250/Makefile        |   1 +
>  include/uapi/linux/serial_core.h        |   3 +
>  6 files changed, 359 insertions(+)
>  create mode 100644 drivers/tty/serial/8250/8250_pci1xxxx.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index abed40db41f0..20da292fcadf 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -13692,6 +13692,13 @@ L:	linux-i2c@vger.kernel.org
>  S:	Maintained
>  F:	drivers/i2c/busses/i2c-mchp-pci1xxxx.c
>  
> +MICROCHIP PCIe UART DRIVER
> +M:	Kumaravel Thiagarajan <kumaravel.thiagarajan@microchip.com>
> +M:	Tharun Kumar P <tharunkumar.pasumarthi@microchip.com>
> +L:	linux-serial@vger.kernel.org
> +S:	Maintained
> +F:	drivers/tty/serial/8250/8250_pci1xxxx.c
> +
>  MICROCHIP PWM DRIVER
>  M:	Claudiu Beznea <claudiu.beznea@microchip.com>
>  L:	linux-arm-kernel@lists.infradead.org (moderated for non-subscribers)
> diff --git a/drivers/tty/serial/8250/8250_pci1xxxx.c b/drivers/tty/serial/8250/8250_pci1xxxx.c
> new file mode 100644
> index 000000000000..ea04c014edb9
> --- /dev/null
> +++ b/drivers/tty/serial/8250/8250_pci1xxxx.c
> @@ -0,0 +1,329 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + *  Probe module for 8250/16550-type MCHP PCI serial ports.
> + *
> + *  Based on drivers/tty/serial/8250/8250_pci.c,
> + *
> + *  Copyright (C) 2022 Microchip Technology Inc., All Rights Reserved.
> + */
> +
> +#include <linux/bitfield.h>
> +#include <linux/bitops.h>
> +#include <linux/io.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/pci.h>
> +#include <linux/serial_core.h>
> +#include <linux/slab.h>
> +#include <linux/string.h>
> +#include <linux/units.h>
> +#include <linux/tty.h>
> +
> +#include <asm/byteorder.h>
> +
> +#include "8250.h"
> +#include "8250_pcilib.h"
> +
> +#define PCI_DEVICE_ID_EFAR_PCI12000		0xa002
> +#define PCI_DEVICE_ID_EFAR_PCI11010		0xa012
> +#define PCI_DEVICE_ID_EFAR_PCI11101		0xa022
> +#define PCI_DEVICE_ID_EFAR_PCI11400		0xa032
> +#define PCI_DEVICE_ID_EFAR_PCI11414		0xa042
> +
> +#define PCI_SUBDEVICE_ID_EFAR_PCI1XXXX_4p	0x0001
> +#define PCI_SUBDEVICE_ID_EFAR_PCI1XXXX_3p012	0x0002
> +#define PCI_SUBDEVICE_ID_EFAR_PCI1XXXX_3p013	0x0003
> +#define PCI_SUBDEVICE_ID_EFAR_PCI1XXXX_3p023	0x0004
> +#define PCI_SUBDEVICE_ID_EFAR_PCI1XXXX_3p123	0x0005
> +#define PCI_SUBDEVICE_ID_EFAR_PCI1XXXX_2p01	0x0006
> +#define PCI_SUBDEVICE_ID_EFAR_PCI1XXXX_2p02	0x0007
> +#define PCI_SUBDEVICE_ID_EFAR_PCI1XXXX_2p03	0x0008
> +#define PCI_SUBDEVICE_ID_EFAR_PCI1XXXX_2p12	0x0009
> +#define PCI_SUBDEVICE_ID_EFAR_PCI1XXXX_2p13	0x000a
> +#define PCI_SUBDEVICE_ID_EFAR_PCI1XXXX_2p23	0x000b
> +#define PCI_SUBDEVICE_ID_EFAR_PCI1XXXX_1p0	0x000c
> +#define PCI_SUBDEVICE_ID_EFAR_PCI1XXXX_1p1	0x000d
> +#define PCI_SUBDEVICE_ID_EFAR_PCI1XXXX_1p2	0x000e
> +#define PCI_SUBDEVICE_ID_EFAR_PCI1XXXX_1p3	0x000f
> +
> +#define PCI_SUBDEVICE_ID_EFAR_PCI12000		PCI_DEVICE_ID_EFAR_PCI12000
> +#define PCI_SUBDEVICE_ID_EFAR_PCI11010		PCI_DEVICE_ID_EFAR_PCI11010
> +#define PCI_SUBDEVICE_ID_EFAR_PCI11101		PCI_DEVICE_ID_EFAR_PCI11101
> +#define PCI_SUBDEVICE_ID_EFAR_PCI11400		PCI_DEVICE_ID_EFAR_PCI11400
> +#define PCI_SUBDEVICE_ID_EFAR_PCI11414		PCI_DEVICE_ID_EFAR_PCI11414
> +
> +#define UART_ACTV_REG				0x11
> +#define UART_BLOCK_SET_ACTIVE			BIT(0)
> +
> +#define UART_PCI_CTRL_REG			0x80
> +#define UART_PCI_CTRL_SET_MULTIPLE_MSI		BIT(4)
> +#define UART_PCI_CTRL_D3_CLK_ENABLE		BIT(0)
> +
> +#define ADCL_CFG_REG				0x40
> +#define ADCL_CFG_POL_SEL			BIT(2)
> +#define ADCL_CFG_PIN_SEL			BIT(1)
> +#define ADCL_CFG_EN				BIT(0)
> +
> +#define UART_BIT_SAMPLE_CNT			16
> +#define BAUD_CLOCK_DIV_INT_MSK			GENMASK(31, 8)
> +#define ADCL_CFG_RTS_DELAY_MASK			GENMASK(11, 8)
> +#define UART_CLOCK_DEFAULT			(62500 * HZ_PER_KHZ)
> +
> +#define UART_WAKE_REG				0x8C
> +#define UART_WAKE_MASK_REG			0x90
> +#define UART_WAKE_N_PIN				BIT(2)
> +#define UART_WAKE_NCTS				BIT(1)
> +#define UART_WAKE_INT				BIT(0)
> +#define UART_WAKE_SRCS	\
> +	(UART_WAKE_N_PIN | UART_WAKE_NCTS | UART_WAKE_INT)
> +
> +#define UART_BAUD_CLK_DIVISOR_REG		0x54
> +
> +#define UART_RESET_REG				0x94
> +#define UART_RESET_D3_RESET_DISABLE		BIT(16)
> +
> +#define MAX_PORTS				4
> +#define PORT_OFFSET				0x100
> +
> +static const int logical_to_physical_port_idx[][MAX_PORTS] = {
> +	{0,  1,  2,  3}, /* PCI12000, PCI11010, PCI11101, PCI11400, PCI11414 */
> +	{0,  1,  2,  3}, /* PCI4p */
> +	{0,  1,  2, -1}, /* PCI3p012 */
> +	{0,  1,  3, -1}, /* PCI3p013 */
> +	{0,  2,  3, -1}, /* PCI3p023 */
> +	{1,  2,  3, -1}, /* PCI3p123 */
> +	{0,  1, -1, -1}, /* PCI2p01 */
> +	{0,  2, -1, -1}, /* PCI2p02 */
> +	{0,  3, -1, -1}, /* PCI2p03 */
> +	{1,  2, -1, -1}, /* PCI2p12 */
> +	{1,  3, -1, -1}, /* PCI2p13 */
> +	{2,  3, -1, -1}, /* PCI2p23 */
> +	{0, -1, -1, -1}, /* PCI1p0 */
> +	{1, -1, -1, -1}, /* PCI1p1 */
> +	{2, -1, -1, -1}, /* PCI1p2 */
> +	{3, -1, -1, -1}, /* PCI1p3 */
> +};
> +
> +struct pci1xxxx_8250 {
> +	unsigned int nr;
> +	void __iomem *membase;
> +	int line[];
> +};
> +
> +static int pci1xxxx_get_num_ports(struct pci_dev *dev)
> +{
> +	switch (dev->subsystem_device) {
> +	case PCI_SUBDEVICE_ID_EFAR_PCI1XXXX_1p0:
> +	case PCI_SUBDEVICE_ID_EFAR_PCI1XXXX_1p1:
> +	case PCI_SUBDEVICE_ID_EFAR_PCI1XXXX_1p2:
> +	case PCI_SUBDEVICE_ID_EFAR_PCI1XXXX_1p3:
> +	case PCI_SUBDEVICE_ID_EFAR_PCI12000:
> +	case PCI_SUBDEVICE_ID_EFAR_PCI11010:
> +	case PCI_SUBDEVICE_ID_EFAR_PCI11101:
> +	case PCI_SUBDEVICE_ID_EFAR_PCI11400:
> +	default:
> +		return 1;
> +	case PCI_SUBDEVICE_ID_EFAR_PCI1XXXX_2p01:
> +	case PCI_SUBDEVICE_ID_EFAR_PCI1XXXX_2p02:
> +	case PCI_SUBDEVICE_ID_EFAR_PCI1XXXX_2p03:
> +	case PCI_SUBDEVICE_ID_EFAR_PCI1XXXX_2p12:
> +	case PCI_SUBDEVICE_ID_EFAR_PCI1XXXX_2p13:
> +	case PCI_SUBDEVICE_ID_EFAR_PCI1XXXX_2p23:
> +		return 2;
> +	case PCI_SUBDEVICE_ID_EFAR_PCI1XXXX_3p012:
> +	case PCI_SUBDEVICE_ID_EFAR_PCI1XXXX_3p123:
> +	case PCI_SUBDEVICE_ID_EFAR_PCI1XXXX_3p013:
> +	case PCI_SUBDEVICE_ID_EFAR_PCI1XXXX_3p023:
> +		return 3;
> +	case PCI_SUBDEVICE_ID_EFAR_PCI1XXXX_4p:
> +	case PCI_SUBDEVICE_ID_EFAR_PCI11414:
> +		return 4;
> +	}
> +}
> +
> +static unsigned int pci1xxxx_get_divisor(struct uart_port *port,
> +					 unsigned int baud, unsigned int *frac)
> +{
> +	unsigned int quot;
> +
> +	/*
> +	 * Calculate baud rate sampling period in nanoseconds.
> +	 * Fractional part x denotes x/255 parts of a nanosecond.
> +	 */
> +	quot = NSEC_PER_SEC / (baud * UART_BIT_SAMPLE_CNT);
> +	*frac = (NSEC_PER_SEC - quot * baud * UART_BIT_SAMPLE_CNT) *
> +		  255 / UART_BIT_SAMPLE_CNT / baud;
> +
> +	return quot;
> +}
> +
> +static void pci1xxxx_set_divisor(struct uart_port *port, unsigned int baud,
> +				 unsigned int quot, unsigned int frac)
> +{
> +	writel(FIELD_PREP(BAUD_CLOCK_DIV_INT_MSK, quot) | frac,
> +	       port->membase + UART_BAUD_CLK_DIVISOR_REG);
> +}
> +
> +static int pci1xxxx_setup(struct pci_dev *pdev,
> +			  struct uart_8250_port *port, int port_idx)
> +{
> +	int ret;
> +
> +	port->port.flags |= UPF_FIXED_TYPE | UPF_SKIP_TEST;
> +	port->port.type = PORT_MCHP16550A;
> +	port->port.set_termios = serial8250_do_set_termios;
> +	port->port.get_divisor = pci1xxxx_get_divisor;
> +	port->port.set_divisor = pci1xxxx_set_divisor;
> +
> +	ret = serial8250_pci_setup_port(pdev, port, 0, PORT_OFFSET * port_idx, 0);
> +	if (ret < 0)
> +		return ret;
> +
> +	writeb(UART_BLOCK_SET_ACTIVE, port->port.membase + UART_ACTV_REG);
> +	writeb(UART_WAKE_SRCS, port->port.membase + UART_WAKE_REG);
> +	writeb(UART_WAKE_N_PIN, port->port.membase + UART_WAKE_MASK_REG);
> +
> +	return 0;
> +}
> +
> +static unsigned int pci1xxxx_get_max_port(int subsys_dev)
> +{
> +	unsigned int i = MAX_PORTS;
> +
> +	if (subsys_dev < ARRAY_SIZE(logical_to_physical_port_idx))
> +		while (i--) {
> +			if (logical_to_physical_port_idx[subsys_dev][i] != -1)
> +				return logical_to_physical_port_idx[subsys_dev][i] + 1;
> +		}
> +
> +	if (subsys_dev == PCI_SUBDEVICE_ID_EFAR_PCI11414)
> +		return 4;
> +
> +	return 1;
> +}
> +
> +static int pci1xxxx_logical_to_physical_port_translate(int subsys_dev, int port)
> +{
> +	if (subsys_dev < ARRAY_SIZE(logical_to_physical_port_idx))
> +		return logical_to_physical_port_idx[subsys_dev][port];
> +
> +	return logical_to_physical_port_idx[0][port];
> +}
> +
> +static int pci1xxxx_serial_probe(struct pci_dev *pdev,
> +				 const struct pci_device_id *id)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct pci1xxxx_8250 *priv;
> +	struct uart_8250_port uart;
> +	unsigned int max_vec_reqd;
> +	unsigned int nr_ports, i;
> +	int num_vectors;
> +	int subsys_dev;
> +	int port_idx;
> +	int rc;
> +
> +	rc = pcim_enable_device(pdev);
> +	if (rc)
> +		return rc;
> +
> +	nr_ports = pci1xxxx_get_num_ports(pdev);
> +
> +	priv = devm_kzalloc(dev, struct_size(priv, line, nr_ports), GFP_KERNEL);
> +	if (!priv)
> +		return -ENOMEM;
> +
> +	priv->membase = pci_ioremap_bar(pdev, 0);
> +	if (!priv->membase)
> +		return -ENOMEM;
> +
> +	pci_set_master(pdev);
> +
> +	priv->nr = nr_ports;
> +
> +	subsys_dev = pdev->subsystem_device;
> +	max_vec_reqd = pci1xxxx_get_max_port(subsys_dev);
> +
> +	num_vectors = pci_alloc_irq_vectors(pdev, 1, max_vec_reqd, PCI_IRQ_ALL_TYPES);
> +	if (num_vectors < 0) {
> +		pci_iounmap(pdev, priv->membase);
> +		return num_vectors;
> +	}
> +
> +	memset(&uart, 0, sizeof(uart));
> +	uart.port.flags = UPF_SHARE_IRQ | UPF_FIXED_PORT;
> +	uart.port.uartclk = UART_CLOCK_DEFAULT;
> +	uart.port.dev = dev;
> +
> +	if (num_vectors == max_vec_reqd)
> +		writeb(UART_PCI_CTRL_SET_MULTIPLE_MSI, priv->membase + UART_PCI_CTRL_REG);
> +
> +	for (i = 0; i < nr_ports; i++) {
> +		priv->line[i] = -ENODEV;
> +
> +		port_idx = pci1xxxx_logical_to_physical_port_translate(subsys_dev, i);
> +
> +		if (num_vectors == max_vec_reqd)
> +			uart.port.irq = pci_irq_vector(pdev, port_idx);
> +		else
> +			uart.port.irq = pci_irq_vector(pdev, 0);
> +
> +		rc = pci1xxxx_setup(pdev, &uart, port_idx);
> +		if (rc) {
> +			dev_warn(dev, "Failed to setup port %u\n", i);
> +			continue;
> +		}
> +
> +		priv->line[i] = serial8250_register_8250_port(&uart);
> +		if (priv->line[i] < 0) {
> +			dev_warn(dev,
> +				"Couldn't register serial port %lx, irq %d, type %d, error %d\n",
> +				uart.port.iobase, uart.port.irq, uart.port.iotype,
> +				priv->line[i]);
> +		}
> +	}
> +
> +	pci_set_drvdata(pdev, priv);
> +
> +	return 0;
> +}
> +
> +static void pci1xxxx_serial_remove(struct pci_dev *dev)
> +{
> +	struct pci1xxxx_8250 *priv = pci_get_drvdata(dev);
> +	unsigned int i;
> +
> +	for (i = 0; i < priv->nr; i++) {
> +		if (priv->line[i] >= 0)
> +			serial8250_unregister_port(priv->line[i]);
> +	}
> +
> +	pci_free_irq_vectors(dev);
> +	pci_iounmap(dev, priv->membase);
> +}
> +
> +static const struct pci_device_id pci1xxxx_pci_tbl[] = {
> +	{ PCI_VDEVICE(EFAR, PCI_DEVICE_ID_EFAR_PCI11010) },
> +	{ PCI_VDEVICE(EFAR, PCI_DEVICE_ID_EFAR_PCI11101) },
> +	{ PCI_VDEVICE(EFAR, PCI_DEVICE_ID_EFAR_PCI11400) },
> +	{ PCI_VDEVICE(EFAR, PCI_DEVICE_ID_EFAR_PCI11414) },
> +	{ PCI_VDEVICE(EFAR, PCI_DEVICE_ID_EFAR_PCI12000) },
> +	{}
> +};
> +MODULE_DEVICE_TABLE(pci, pci1xxxx_pci_tbl);
> +
> +static struct pci_driver pci1xxxx_pci_driver = {
> +	.name = "pci1xxxx serial",
> +	.probe = pci1xxxx_serial_probe,
> +	.remove = pci1xxxx_serial_remove,
> +	.id_table = pci1xxxx_pci_tbl,
> +};
> +module_pci_driver(pci1xxxx_pci_driver);
> +
> +static_assert((ARRAY_SIZE(logical_to_physical_port_idx) == PCI_SUBDEVICE_ID_EFAR_PCI1XXXX_1p3 + 1));
> +
> +MODULE_IMPORT_NS(SERIAL_8250_PCI);
> +MODULE_DESCRIPTION("Microchip Technology Inc. PCIe to UART module");
> +MODULE_AUTHOR("Kumaravel Thiagarajan <kumaravel.thiagarajan@microchip.com>");
> +MODULE_AUTHOR("Tharun Kumar P <tharunkumar.pasumarthi@microchip.com>");
> +MODULE_LICENSE("GPL");
> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> index 33be7aad11ef..bb375a7f0328 100644
> --- a/drivers/tty/serial/8250/8250_port.c
> +++ b/drivers/tty/serial/8250/8250_port.c
> @@ -313,6 +313,14 @@ static const struct serial8250_config uart_config[] = {
>  		.rxtrig_bytes	= {1, 4, 8, 14},
>  		.flags		= UART_CAP_FIFO,
>  	},
> +	[PORT_MCHP16550A] = {
> +		.name           = "MCHP16550A",
> +		.fifo_size      = 256,
> +		.tx_loadsz      = 256,
> +		.fcr            = UART_FCR_ENABLE_FIFO | UART_FCR_R_TRIG_01,
> +		.rxtrig_bytes   = {2, 66, 130, 194},
> +		.flags          = UART_CAP_FIFO,
> +	},
>  };
>  
>  /* Uart divisor latch read */
> diff --git a/drivers/tty/serial/8250/Kconfig b/drivers/tty/serial/8250/Kconfig
> index 9b3ba28cc562..978dc196c29b 100644
> --- a/drivers/tty/serial/8250/Kconfig
> +++ b/drivers/tty/serial/8250/Kconfig
> @@ -295,6 +295,17 @@ config SERIAL_8250_HUB6
>  	  To compile this driver as a module, choose M here: the module
>  	  will be called 8250_hub6.
>  
> +config SERIAL_8250_PCI1XXXX
> +	tristate "Microchip 8250 based serial port"
> +	depends on SERIAL_8250 && PCI
> +	select SERIAL_8250_PCILIB
> +	default SERIAL_8250
> +	help
> +	 Select this option if you have a setup with Microchip PCIe
> +	 Switch with serial port enabled and wish to enable 8250
> +	 serial driver for the serial interface. This driver support
> +	 will ensure to support baud rates upto 1.5Mpbs.
> +
>  #
>  # Misc. options/drivers.
>  #
> diff --git a/drivers/tty/serial/8250/Makefile b/drivers/tty/serial/8250/Makefile
> index ce63a250da3b..4fc2fc1f41b6 100644
> --- a/drivers/tty/serial/8250/Makefile
> +++ b/drivers/tty/serial/8250/Makefile
> @@ -27,6 +27,7 @@ obj-$(CONFIG_SERIAL_8250_ACCENT)	+= 8250_accent.o
>  obj-$(CONFIG_SERIAL_8250_BOCA)		+= 8250_boca.o
>  obj-$(CONFIG_SERIAL_8250_EXAR_ST16C554)	+= 8250_exar_st16c554.o
>  obj-$(CONFIG_SERIAL_8250_HUB6)		+= 8250_hub6.o
> +obj-$(CONFIG_SERIAL_8250_PCI1XXXX)	+= 8250_pci1xxxx.o
>  obj-$(CONFIG_SERIAL_8250_FSL)		+= 8250_fsl.o
>  obj-$(CONFIG_SERIAL_8250_MEN_MCB)	+= 8250_men_mcb.o
>  obj-$(CONFIG_SERIAL_8250_DFL)		+= 8250_dfl.o
> diff --git a/include/uapi/linux/serial_core.h b/include/uapi/linux/serial_core.h
> index 3ba34d8378bd..281fa286555c 100644
> --- a/include/uapi/linux/serial_core.h
> +++ b/include/uapi/linux/serial_core.h
> @@ -207,6 +207,9 @@
>  /* Atheros AR933X SoC */
>  #define PORT_AR933X	99
>  
> +/* MCHP 16550A UART with 256 byte FIFOs */
> +#define PORT_MCHP16550A	100
> +
>  /* ARC (Synopsys) on-chip UART */
>  #define PORT_ARC       101
>  
> -- 
> 2.25.1
>