2017-02-10 16:49 GMT+01:00 Ludovic Desroches <ludovic.desroches@xxxxxxxxxxxxx>:
> On Fri, Feb 10, 2017 at 04:24:46PM +0100, Romain Izard wrote:
>> The fractional baud rate generator is available when using the
>> asynchronous mode of Atmel USART controllers. It makes it possible to
>> use higher baudrates, in exchange for a less precise clock with a
>> variable duty cycle.
>>
>> The existing code restricts its use to the normal mode of the USART
>> controller, following the recommendation from the datasheet for the
>> first chip embedding this type of controller. This recommendation has
>> been removed from the documentation for the newer chips. After
>> verification, all revisions of this controller should be able to use the
>> fractional baud rate generator with the different asynchronous modes.
>>
>> Removing the condition on ATMEL_US_USMODE makes it possible to get
>> correct baudrates at high speed in more cases.
>>
>> This was tested with a board using an Atmel SAMA5D2 chip and a TI
>> WL1831 WiFi/Bluetooth combo chip at 3 Mbauds, with hardware flow control
>> enabled.
>>
>> Signed-off-by: Romain Izard <romain.izard.pro@xxxxxxxxx>
>
> Acked-by: Ludovic Desroches <ludovic.desroches@xxxxxxxxxxxxx>
Signed-off-by: Richard Genoud <richard.genoud@xxxxxxxxx>
Thanks !
> Thanks
>
>> ---
>> drivers/tty/serial/atmel_serial.c | 7 ++++---
>> 1 file changed, 4 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
>> index fabbe76203bb..6684456dca9e 100644
>> --- a/drivers/tty/serial/atmel_serial.c
>> +++ b/drivers/tty/serial/atmel_serial.c
>> @@ -1758,7 +1758,9 @@ static void atmel_get_ip_name(struct uart_port *port)
>>
>> /*
>> * Only USART devices from at91sam9260 SOC implement fractional
>> - * baudrate.
>> + * baudrate. It is available for all asynchronous modes, with the
>> + * following restriction: the sampling clock's duty cycle is not
>> + * constant.
>> */
>> atmel_port->has_frac_baudrate = false;
>> atmel_port->has_hw_timer = false;
>> @@ -2202,8 +2204,7 @@ static void atmel_set_termios(struct uart_port *port, struct ktermios *termios,
>> * then
>> * 8 CD + FP = selected clock / (2 * baudrate)
>> */
>> - if (atmel_port->has_frac_baudrate &&
>> - (mode & ATMEL_US_USMODE) == ATMEL_US_USMODE_NORMAL) {
>> + if (atmel_port->has_frac_baudrate) {
>> div = DIV_ROUND_CLOSEST(port->uartclk, baud * 2);
>> cd = div >> 3;
>> fp = div & ATMEL_US_FP_MASK;
>> --
>> 2.9.3
>>
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