Commit bdc5f300 authored by Martin Sperl's avatar Martin Sperl Committed by Greg Kroah-Hartman
Browse files

serial: bcm2835: add driver for bcm2835-aux-uart 



The bcm2835 SOC contains an auxiliary uart, which is very close
to the ns16550 with some differences.

The big difference is that the uart HW is not using an internal divider
of 16 but 8, which results in an effictive baud-rate being twice
the requested baud-rate.

This driver handles this device correctly and handles the difference in
the HW divider by scaling up the clock by a factor of 2.

The approach to write a separate (wrapper) driver instead of using a
multiplying clock and "ns16550" as compatibility in the device-tree
has been recommended by Stephen Warren.

Signed-off-by: default avatarMartin Sperl <kernel@martin.sperl.org>
Acked-by: default avatarEric Anholt <eric@anholt.net>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 45d7e9a5

drivers/tty/serial/8250/8250_bcm2835aux.c

0 → 100644
+146 −0
Original line number Diff line number Diff line 
/*

 * Serial port driver for BCM2835AUX UART

 *

 * Copyright (C) 2016 Martin Sperl <kernel@martin.sperl.org>

 *

 * Based on 8250_lpc18xx.c:

 * Copyright (C) 2015 Joachim Eastwood <manabian@gmail.com>

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License version 2 as

 * published by the Free Software Foundation.

 *

 */



#include <linux/clk.h>

#include <linux/io.h>

#include <linux/module.h>

#include <linux/of.h>

#include <linux/platform_device.h>



#include "8250.h"



struct bcm2835aux_data {

	struct uart_8250_port uart;

	struct clk *clk;

	int line;

};



static int bcm2835aux_serial_probe(struct platform_device *pdev)

{

	struct bcm2835aux_data *data;

	struct resource *res;

	int ret;



	/* allocate the custom structure */

	data = devm_kzalloc(&pdev->dev, sizeof(*data), GFP_KERNEL);

	if (!data)

		return -ENOMEM;



	/* initialize data */

	spin_lock_init(&data->uart.port.lock);

	data->uart.capabilities = UART_CAP_FIFO;

	data->uart.port.dev = &pdev->dev;

	data->uart.port.regshift = 2;

	data->uart.port.type = PORT_16550;

	data->uart.port.iotype = UPIO_MEM;

	data->uart.port.fifosize = 8;

	data->uart.port.flags = UPF_SHARE_IRQ |

				UPF_FIXED_PORT |

				UPF_FIXED_TYPE |

				UPF_SKIP_TEST;



	/* get the clock - this also enables the HW */

	data->clk = devm_clk_get(&pdev->dev, NULL);

	ret = PTR_ERR_OR_ZERO(data->clk);

	if (ret) {

		dev_err(&pdev->dev, "could not get clk: %d\n", ret);

		return ret;

	}



	/* get the interrupt */

	data->uart.port.irq = platform_get_irq(pdev, 0);

	if (data->uart.port.irq < 0) {

		dev_err(&pdev->dev, "irq not found - %i",

			data->uart.port.irq);

		return data->uart.port.irq;

	}



	/* map the main registers */

	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);

	if (!res) {

		dev_err(&pdev->dev, "memory resource not found");

		return -EINVAL;

	}

	data->uart.port.membase = devm_ioremap_resource(&pdev->dev, res);

	ret = PTR_ERR_OR_ZERO(data->uart.port.membase);

	if (ret)

		return ret;



	/* Check for a fixed line number */

	ret = of_alias_get_id(pdev->dev.of_node, "serial");

	if (ret >= 0)

		data->uart.port.line = ret;



	/* enable the clock as a last step */

	ret = clk_prepare_enable(data->clk);

	if (ret) {

		dev_err(&pdev->dev, "unable to enable uart clock - %d\n",

			ret);

		return ret;

	}



	/* the HW-clock divider for bcm2835aux is 8,

	 * but 8250 expects a divider of 16,

	 * so we have to multiply the actual clock by 2

	 * to get identical baudrates.

	 */

	data->uart.port.uartclk = clk_get_rate(data->clk) * 2;



	/* register the port */

	ret = serial8250_register_8250_port(&data->uart);

	if (ret < 0) {

		dev_err(&pdev->dev, "unable to register 8250 port - %d\n",

			ret);

		goto dis_clk;

	}

	data->line = ret;



	platform_set_drvdata(pdev, data);



	return 0;



dis_clk:

	clk_disable_unprepare(data->clk);

	return ret;

}



static int bcm2835aux_serial_remove(struct platform_device *pdev)

{

	struct bcm2835aux_data *data = platform_get_drvdata(pdev);



	serial8250_unregister_port(data->uart.port.line);

	clk_disable_unprepare(data->clk);



	return 0;

}



static const struct of_device_id bcm2835aux_serial_match[] = {

	{ .compatible = "brcm,bcm2835-aux-uart" },

	{ },

};

MODULE_DEVICE_TABLE(of, bcm2835aux_serial_match);



static struct platform_driver bcm2835aux_serial_driver = {

	.driver = {

		.name = "bcm2835-aux-uart",

		.of_match_table = bcm2835aux_serial_match,

	},

	.probe  = bcm2835aux_serial_probe,

	.remove = bcm2835aux_serial_remove,

};

module_platform_driver(bcm2835aux_serial_driver);



MODULE_DESCRIPTION("BCM2835 auxiliar UART driver");

MODULE_AUTHOR("Martin Sperl <kernel@martin.sperl.org>");

MODULE_LICENSE("GPL v2");

drivers/tty/serial/8250/Kconfig

+24 −0
Original line number Diff line number Diff line
@@ -272,6 +272,30 @@ config SERIAL_8250_ACORN 
	  system, say Y to this option.  The driver can handle 1, 2, or 3 port

	  cards.  If unsure, say N.



config SERIAL_8250_BCM2835AUX

	tristate "BCM2835 auxiliar mini UART support"

	depends on ARCH_BCM2835 || COMPILE_TEST

	depends on SERIAL_8250 && SERIAL_8250_SHARE_IRQ

	help

	  Support for the BCM2835 auxiliar mini UART.



	  Features and limitations of the UART are

	    Registers are similar to 16650 registers,

              set bits in the control registers that are unsupported

	      are ignored and read back as 0

	    7/8 bit operation with 1 start and 1 stop bit

	    8 symbols deep fifo for rx and tx

	    SW controlled RTS and SW readable CTS

	    Clock rate derived from system clock

	    Uses 8 times oversampling (compared to 16 times for 16650)

	    Missing break detection (but break generation)

	    Missing framing error detection

	    Missing parity bit

	    Missing receive time-out interrupt

	    Missing DCD, DSR, DTR and RI signals



	  If unsure, say N.



config SERIAL_8250_FSL

	bool

	depends on SERIAL_8250_CONSOLE

drivers/tty/serial/8250/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -12,6 +12,7 @@ obj-$(CONFIG_SERIAL_8250_PCI) += 8250_pci.o 
obj-$(CONFIG_SERIAL_8250_HP300)		+= 8250_hp300.o

obj-$(CONFIG_SERIAL_8250_CS)		+= serial_cs.o

obj-$(CONFIG_SERIAL_8250_ACORN)		+= 8250_acorn.o

obj-$(CONFIG_SERIAL_8250_BCM2835AUX)	+= 8250_bcm2835aux.o

obj-$(CONFIG_SERIAL_8250_CONSOLE)	+= 8250_early.o

obj-$(CONFIG_SERIAL_8250_FOURPORT)	+= 8250_fourport.o

obj-$(CONFIG_SERIAL_8250_ACCENT)	+= 8250_accent.o

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