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Commit c73942e2 authored by Heikki Krogerus's avatar Heikki Krogerus Committed by Greg Kroah-Hartman
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serial: 8250_dw: proper support for UARTs without busy functionality 



If the DW_apb_uart is configured with UART_16550_COMPATIBLE
configuration parameter set, then the Busy Functionality is
not available. These UARTs will never generate the Busy
detect indication interrupt, and therefore don't need
handling for it.

This creates a small optimization for the DW_apb_uarts
configured without the busy functionality, but more
importantly, it removes the small but real risk of hitting
potential issues caused by busy functionality handling when
no busy functionality exist.

Signed-off-by: default avatarHeikki Krogerus <heikki.krogerus@linux.intel.com>
Reviewed-by: default avatarAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 9e08fa50

Documentation/devicetree/bindings/serial/snps-dw-apb-uart.txt

+3 −0
Original line number Diff line number Diff line
@@ -15,6 +15,9 @@ The supplying peripheral clock can also be handled, needing a second property 
	Required elements: "baudclk", "apb_pclk"



Optional properties:

- snps,uart-16550-compatible : reflects the value of UART_16550_COMPATIBLE

  configuration parameter. Define this if your UART does not implement the busy

  functionality.

- resets : phandle to the parent reset controller.

- reg-shift : quantity to shift the register offsets by.  If this property is

  not present then the register offsets are not shifted.

drivers/tty/serial/8250/8250_dw.c

+12 −1
Original line number Diff line number Diff line
@@ -65,6 +65,7 @@ struct dw8250_data { 
	struct uart_8250_dma	dma;



	unsigned int		skip_autocfg:1;

	unsigned int		uart_16550_compatible:1;

};



#define BYT_PRV_CLK			0x800
@@ -317,8 +318,9 @@ static void dw8250_quirks(struct uart_port *p, struct dw8250_data *data) 
		p->iotype = UPIO_MEM32;

		p->regshift = 2;

		p->serial_in = dw8250_serial_in32;

		p->serial_out = dw8250_serial_out32;

		p->set_termios = dw8250_set_termios;

		/* So far none of there implement the Busy Functionality */

		data->uart_16550_compatible = true;

	}



	/* Platforms with iDMA */
@@ -375,6 +377,9 @@ static int dw8250_probe(struct platform_device *pdev) 
	data->usr_reg = DW_UART_USR;

	p->private_data = data;



	data->uart_16550_compatible = device_property_read_bool(p->dev,

						"snps,uart-16550-compatible");



	err = device_property_read_u32(p->dev, "reg-shift", &val);

	if (!err)

		p->regshift = val;
@@ -461,6 +466,12 @@ static int dw8250_probe(struct platform_device *pdev) 


	dw8250_quirks(p, data);



	/* If the Busy Functionality is not implemented, don't handle it */

	if (data->uart_16550_compatible) {

		p->serial_out = NULL;

		p->handle_irq = NULL;

	}



	if (!data->skip_autocfg)

		dw8250_setup_port(&uart);