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serial: imx: fix data breakage on termios change 

imx_set_termios(): avoid writing baud rate divider registers when the
values to be written are the same as current. Any writing seems to
restart transmission/receiving logic in the hardware, that leads to
data breakage even when rate doesn't in fact change. E.g., user
switches RTS/CTS handshake and suddenly gets broken bytes.

Signed-off-by: Sergey Organov <sorganov@gmail.com>
Link: https://lore.kernel.org/r/1567017475-11919-5-git-send-email-sorganov@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Sergey Organov 2019-08-28 21:37:54 +03:00 committed by Greg Kroah-Hartman
parent 85f30fbf32
commit d47bcb4a6c
1 changed files with 16 additions and 3 deletions
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19
drivers/tty/serial/imx.c
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@ -1545,7 +1545,7 @@ imx_uart_set_termios(struct uart_port *port, struct ktermios *termios,
unsigned int baud, quot;
unsigned int old_csize = old ? old->c_cflag & CSIZE : CS8;
unsigned long div;
unsigned long num, denom;
unsigned long num, denom, old_ubir, old_ubmr;
uint64_t tdiv64;
/*
@ -1670,8 +1670,21 @@ imx_uart_set_termios(struct uart_port *port, struct ktermios *termios,
ufcr = (ufcr & (~UFCR_RFDIV)) | UFCR_RFDIV_REG(div);
imx_uart_writel(sport, ufcr, UFCR);
imx_uart_writel(sport, num, UBIR);
imx_uart_writel(sport, denom, UBMR);
/*
* Two registers below should always be written both and in this
* particular order. One consequence is that we need to check if any of
* them changes and then update both. We do need the check for change
* as even writing the same values seem to "restart"
* transmission/receiving logic in the hardware, that leads to data
* breakage even when rate doesn't in fact change. E.g., user switches
* RTS/CTS handshake and suddenly gets broken bytes.
*/
old_ubir = imx_uart_readl(sport, UBIR);
old_ubmr = imx_uart_readl(sport, UBMR);
if (old_ubir != num || old_ubmr != denom) {
imx_uart_writel(sport, num, UBIR);
imx_uart_writel(sport, denom, UBMR);
}
if (!imx_uart_is_imx1(sport))
imx_uart_writel(sport, sport->port.uartclk / div / 1000,