[linux-yocto] [PATCH 11/18] serial: 8250_dw: proper support for UARTs without busy functionality

[Tan Jui Nee]

From: Heikki Krogerus <heikki.krogerus at linux.intel.com>

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: Heikki Krogerus <heikki.krogerus at linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko at linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
(cherry picked from commit c73942e22aa4a3d910f9be8d48de4080c3a52086)
Signed-off-by: Tan Jui Nee <jui.nee.tan at intel.com>
---
 .../devicetree/bindings/serial/snps-dw-apb-uart.txt         |  3 +++
 drivers/tty/serial/8250/8250_dw.c                           | 13 ++++++++++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.txt b/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.txt
index 289c40e..12bbe9f 100644
--- a/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.txt
+++ b/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.txt
@@ -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.
diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
index c5907a7..a4aa671 100644
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -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
@@ -313,8 +314,9 @@ 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 */
@@ -371,6 +373,9 @@ 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;
@@ -457,6 +462,12 @@ 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);
 
-- 
1.9.1