mips: msp71xx/serial: add workaround for DW UART

The Synopsys DesignWare UART in pmc-sierra msp71xx has an extra feature
where the UART detects a write attempt to the LCR whilst busy and raises
an interrupt.  The driver needs to clear the interrupt and rewrite the
LCR.  Move this into platform code and out of the 8250 driver.

Acked-by: Ralf Baechle <ralf@linux-mips.org>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Jamie Iles <jamie@jamieiles.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 65 insertions, 4 deletions

diff --git a/arch/mips/pmc-sierra/msp71xx/msp_serial.c b/arch/mips/pmc-sierra/msp71xx/msp_serial.c
index c3247b5801f1..a1c7c7da2336 100644
--- a/arch/mips/pmc-sierra/msp71xx/msp_serial.c
+++ b/arch/mips/pmc-sierra/msp71xx/msp_serial.c
@@ -27,6 +27,7 @@
 #include <linux/serial.h>
 #include <linux/serial_core.h>
 #include <linux/serial_reg.h>
+#include <linux/slab.h>
 
 #include <asm/bootinfo.h>
 #include <asm/io.h>
@@ -38,6 +39,55 @@
 #include <msp_int.h>
 #include <msp_regs.h>
 
+struct msp_uart_data {
+        int     last_lcr;
+};
+
+static void msp_serial_out(struct uart_port *p, int offset, int value)
+{
+        struct msp_uart_data *d = p->private_data;
+
+        if (offset == UART_LCR)
+                d->last_lcr = value;
+
+        offset <<= p->regshift;
+        writeb(value, p->membase + offset);
+}
+
+static unsigned int msp_serial_in(struct uart_port *p, int offset)
+{
+        offset <<= p->regshift;
+
+        return readb(p->membase + offset);
+}
+
+static int msp_serial_handle_irq(struct uart_port *p)
+{
+        struct msp_uart_data *d = p->private_data;
+        unsigned int iir = readb(p->membase + (UART_IIR << p->regshift));
+
+        if (serial8250_handle_irq(p, iir)) {
+                return 1;
+        } else if ((iir & UART_IIR_BUSY) == UART_IIR_BUSY) {
+                /*
+                 * The DesignWare APB UART has an Busy Detect (0x07) interrupt
+                 * meaning an LCR write attempt occurred while the UART was
+                 * busy. The interrupt must be cleared by reading the UART
+                 * status register (USR) and the LCR re-written.
+                 *
+                 * Note: MSP reserves 0x20 bytes of address space for the UART
+                 * and the USR is mapped in a separate block at an offset of
+                 * 0xc0 from the start of the UART.
+                 */
+                (void)readb(p->membase + 0xc0);
+                writeb(d->last_lcr, p->membase + (UART_LCR << p->regshift));
+
+                return 1;
+        }
+
+        return 0;
+}
+
 void __init msp_serial_setup(void)
 {
         char    *s;
@@ -59,13 +109,22 @@ void __init msp_serial_setup(void)
         up.irq          = MSP_INT_UART0;
         up.uartclk      = uartclk;
         up.regshift     = 2;
-        up.iotype       = UPIO_DWAPB; /* UPIO_MEM like */
+        up.iotype       = UPIO_MEM;
         up.flags        = ASYNC_BOOT_AUTOCONF | ASYNC_SKIP_TEST;
         up.type         = PORT_16550A;
         up.line         = 0;
-        up.private_data         = (void*)UART0_STATUS_REG;
-        if (early_serial_setup(&up))
+        up.serial_out   = msp_serial_out;
+        up.serial_in    = msp_serial_in;
+        up.handle_irq   = msp_serial_handle_irq;
+        up.private_data = kzalloc(sizeof(struct msp_uart_data), GFP_KERNEL);
+        if (!up.private_data) {
+                pr_err("failed to allocate uart private data\n");
+                return;
+        }
+        if (early_serial_setup(&up)) {
+                kfree(up.private_data);
                 pr_err("Early serial init of port 0 failed\n");
+        }
 
         /* Initialize the second serial port, if one exists */
         switch (mips_machtype) {
@@ -88,6 +147,8 @@ void __init msp_serial_setup(void)
         up.irq          = MSP_INT_UART1;
         up.line         = 1;
         up.private_data         = (void*)UART1_STATUS_REG;
-        if (early_serial_setup(&up))
+        if (early_serial_setup(&up)) {
+                kfree(up.private_data);
                 pr_err("Early serial init of port 1 failed\n");
+        }
 }