[PATCH linux-next 1/1] tty/serial: at91: fix I/O accesses on RHR and THR for AVR32

[Cyrille Pitchen]

This patch fixes I/O accesses on the Receiver Holding Register and on the
Transmitter Holding Register. Indeed AVR32 can only perform 32bit I/O
accesses on registers: using 8bit I/O accesses would read or write garbage
data.

Fixes: commit b5199d468177 ("tty/serial: at91: add support to FIFOs")
Signed-off-by: Cyrille Pitchen <cyrille.pitchen at atmel.com>
---
Hi all,

this patch fixes a bug on AVR32 introduced by the support of FIFOs for
AT91. Indeed when FIFOs are enabled they work in Multiple Data mode.
The Multiple Data mode allows to read up to 4 data from the Receiver
Holding Register (RHR) or write up to 4 data into the Transmitter Holding
Register (THR) in a single I/O access. Hence when only one data is to be
read from the RHR or written into the THR, the driver cannot use 32bit I/O
access anymore but must use 8bit I/O access instead.

For ARM-base AT91 SoCs, 8bit I/O accesses can always be used even when
FIFOs are not available. However AV32 can only use 32bit I/O accesses.

Since atmel_uart_readb(), resp. atmel_uart_writeb(), was created by the
FIFO support patch to access the RHR, resp. the THR, this patch replaces
it by atmel_uart_read_char(), resp. atmel_uart_write_char(). Hence the
actual width of the I/O access now depends only on the architecture.

All registers but RHR and THR use 32bit I/O accesses.

This patch was tested on a at91sam9260ek board.

Best Regards,

Cyrille

ChangeLog:

v1: initial version

 drivers/tty/serial/atmel_serial.c | 37 +++++++++++++++++++++++++++----------
 1 file changed, 27 insertions(+), 10 deletions(-)

diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
index e91b3b2f0590..5ca5cf3e9359 100644
--- a/drivers/tty/serial/atmel_serial.c
+++ b/drivers/tty/serial/atmel_serial.c
@@ -204,16 +204,33 @@ static inline void atmel_uart_writel(struct uart_port *port, u32 reg, u32 value)
 	__raw_writel(value, port->membase + reg);
 }
 
-static inline u8 atmel_uart_readb(struct uart_port *port, u32 reg)
+#ifdef CONFIG_AVR32
+
+/* AVR32 cannot handle 8 or 16bit I/O accesses but only 32bit I/O accesses */
+static inline u8 atmel_uart_read_char(struct uart_port *port)
+{
+	return __raw_readl(port->membase + ATMEL_US_RHR);
+}
+
+static inline void atmel_uart_write_char(struct uart_port *port, u8 value)
 {
-	return __raw_readb(port->membase + reg);
+	__raw_writel(value, port->membase + ATMEL_US_THR);
 }
 
-static inline void atmel_uart_writeb(struct uart_port *port, u32 reg, u8 value)
+#else
+
+static inline u8 atmel_uart_read_char(struct uart_port *port)
 {
-	__raw_writeb(value, port->membase + reg);
+	return __raw_readb(port->membase + ATMEL_US_RHR);
 }
 
+static inline void atmel_uart_write_char(struct uart_port *port, u8 value)
+{
+	__raw_writeb(value, port->membase + ATMEL_US_THR);
+}
+
+#endif
+
 #ifdef CONFIG_SERIAL_ATMEL_PDC
 static bool atmel_use_pdc_rx(struct uart_port *port)
 {
@@ -658,7 +675,7 @@ static void atmel_rx_chars(struct uart_port *port)
 
 	status = atmel_uart_readl(port, ATMEL_US_CSR);
 	while (status & ATMEL_US_RXRDY) {
-		ch = atmel_uart_readb(port, ATMEL_US_RHR);
+		ch = atmel_uart_read_char(port);
 
 		/*
 		 * note that the error handling code is
@@ -709,7 +726,7 @@ static void atmel_tx_chars(struct uart_port *port)
 
 	if (port->x_char &&
 	    (atmel_uart_readl(port, ATMEL_US_CSR) & atmel_port->tx_done_mask)) {
-		atmel_uart_writeb(port, ATMEL_US_THR, port->x_char);
+		atmel_uart_write_char(port, port->x_char);
 		port->icount.tx++;
 		port->x_char = 0;
 	}
@@ -718,7 +735,7 @@ static void atmel_tx_chars(struct uart_port *port)
 
 	while (atmel_uart_readl(port, ATMEL_US_CSR) &
 	       atmel_port->tx_done_mask) {
-		atmel_uart_writeb(port, ATMEL_US_THR, xmit->buf[xmit->tail]);
+		atmel_uart_write_char(port, xmit->buf[xmit->tail]);
 		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
 		port->icount.tx++;
 		if (uart_circ_empty(xmit))
@@ -2294,7 +2311,7 @@ static int atmel_poll_get_char(struct uart_port *port)
 	while (!(atmel_uart_readl(port, ATMEL_US_CSR) & ATMEL_US_RXRDY))
 		cpu_relax();
 
-	return atmel_uart_readb(port, ATMEL_US_RHR);
+	return atmel_uart_read_char(port);
 }
 
 static void atmel_poll_put_char(struct uart_port *port, unsigned char ch)
@@ -2302,7 +2319,7 @@ static void atmel_poll_put_char(struct uart_port *port, unsigned char ch)
 	while (!(atmel_uart_readl(port, ATMEL_US_CSR) & ATMEL_US_TXRDY))
 		cpu_relax();
 
-	atmel_uart_writeb(port, ATMEL_US_THR, ch);
+	atmel_uart_write_char(port, ch);
 }
 #endif
 
@@ -2409,7 +2426,7 @@ static void atmel_console_putchar(struct uart_port *port, int ch)
 {
 	while (!(atmel_uart_readl(port, ATMEL_US_CSR) & ATMEL_US_TXRDY))
 		cpu_relax();
-	atmel_uart_writeb(port, ATMEL_US_THR, ch);
+	atmel_uart_write_char(port, ch);
 }
 
 /*
-- 
1.8.2.2