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

[Alexandre Belloni]

On 30/07/2015 at 16:33:38 +0200, Cyrille Pitchen wrote :
> 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>
Acked-by: Alexandre Belloni <alexandre.belloni at free-electrons.com>

Also, tested on at91rm9200ek.

> ---
> 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
> 

-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com