[Xen-devel] [PATCH v2] xen/serial: setup UART idle mode for OMAP

[Oleksandr Dmytryshyn <oleksandr.dmytryshyn@xxxxxxxxxxxxxxx>]

UART is not able to receive bytes when idle mode is not
configured properly. When we use Xen with old Linux
Kernel (for example 3.8) this kernel configures hwmods
for all devices even if the device tree nodes for those
devices is absent in device tree. Thus UART idle mode
is configured too. The fake node for the UART should
be added to the device tree because the MMIO range
is not mapped by Xen. So UART works normally in this
case. But new Linux Kernel (3.12 and upper) doesn't
configure idle mode for UART and UART can not work
normally in this case.

Signed-off-by: Oleksandr Dmytryshyn <oleksandr.dmytryshyn@xxxxxxxxxxxxxxx>
---
Changed since v1:
 * corrected commit message

 xen/drivers/char/omap-uart.c | 3 +++
 xen/include/xen/8250-uart.h  | 4 ++++
 2 files changed, 7 insertions(+)

diff --git a/xen/drivers/char/omap-uart.c b/xen/drivers/char/omap-uart.c
index a798b8d..16d1454 100644
--- a/xen/drivers/char/omap-uart.c
+++ b/xen/drivers/char/omap-uart.c
@@ -195,6 +195,9 @@ static void __init omap_uart_init_preirq(struct serial_port 
*port)
     omap_write(uart, UART_MCR, UART_MCR_DTR|UART_MCR_RTS);
 
     omap_write(uart, UART_OMAP_MDR1, UART_OMAP_MDR1_16X_MODE);
+
+    /* setup iddle mode */
+    omap_write(uart, UART_SYSC, OMAP_UART_SYSC_DEF_CONF);
 }
 
 static void __init omap_uart_init_postirq(struct serial_port *port)
diff --git a/xen/include/xen/8250-uart.h b/xen/include/xen/8250-uart.h
index a682bae..304b9dd 100644
--- a/xen/include/xen/8250-uart.h
+++ b/xen/include/xen/8250-uart.h
@@ -32,6 +32,7 @@
 #define UART_MCR          0x04    /* Modem control        */
 #define UART_LSR          0x05    /* line status          */
 #define UART_MSR          0x06    /* Modem status         */
+#define UART_SYSC         0x15    /* System configuration register */
 #define UART_USR          0x1f    /* Status register (DW) */
 #define UART_DLL          0x00    /* divisor latch (ls) (DLAB=1) */
 #define UART_DLM          0x01    /* divisor latch (ms) (DLAB=1) */
@@ -145,6 +146,9 @@
 /* SCR register bitmasks */
 #define OMAP_UART_SCR_RX_TRIG_GRANU1_MASK (1 << 7)
 
+/* System configuration register */
+#define OMAP_UART_SYSC_DEF_CONF 0x0d /* autoidle mode, wakeup is enabled */
+
 #endif /* __XEN_8250_UART_H__ */
 
 /*
-- 
1.9.1


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