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: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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 (file)
--- 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 5c6a819..7ed0580 100644 (file)
--- 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
@@ -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);