[PATCH 0/3] serial: Fix support for UPF_SPD_* flags

["Pali Rohár" <pali@kernel.org>]

Support for UPF_SPD_* flags is currently broken in more drivers for two
reasons. First one is that uart_update_timeout() function does not
calculate timeout for UPF_SPD_CUST flag correctly. Second reason is that
userspace termios structre is modified by most drivers after each
TIOCSSERIAL or TCSETS call to discard activation of UPF_SPD_* flags.

Reproducer for these issues:

  #include <termios.h>
  #include <sys/ioctl.h>
  #include <asm/ioctls.h>
  #include <linux/serial.h>

  static unsigned cdiv(unsigned a, unsigned b) {
    if (!b) return b;
    return (a + (b/2)) / b;
  }

  void set_active_spd_cust_baud(int fd, unsigned baudrate) {
    struct serial_struct serial;
    struct termios termios;
    tcgetattr(fd, &termios);
    ioctl(fd, TIOCGSERIAL, &serial);
    serial.flags &= ~ASYNC_SPD_MASK;
    serial.flags |= ASYNC_SPD_CUST;
    serial.custom_divisor = cdiv(serial.baud_base, baudrate);
    ioctl(fd, TIOCSSERIAL, &serial);
    cfsetspeed(&termios, B38400);
    tcsetattr(fd, TCSANOW, &termios);
  }

  int is_spd_cust_active(int fd) {
    struct serial_struct serial;
    struct termios termios;
    tcgetattr(fd, &termios);
    ioctl(fd, TIOCGSERIAL, &serial);
    return
      (serial.flags & ASYNC_SPD_MASK) == ASYNC_SPD_CUST &&
      cfgetospeed(&termios) == B38400;
  }

(error handling was ommited for simplification)

After calling set_active_spd_cust_baud() function SPD custom divisor
should be active and therefore is_spd_cust_active() should return true.

But it is not active (cfgetospeed does not return B38400) and this patch
series should fix it. I have tested it with 8250 driver.


Originally Johan Hovold reported that there may be issue with these
ASYNC_SPD_FLAGS in email:
https://lore.kernel.org/linux-serial/20211007133146.28949-1-johan@kernel.org/


Johan, Greg, could you please test these patches if there is not any
regression?


Pali Rohár (3):
  serial: core: Document why UPF_SPD_CUST is not handled in
    uart_get_baud_rate()
  serial: core: Fix function uart_update_timeout() to handle
    UPF_SPD_CUST flag
  serial: Fix support for UPF_SPD_* flags in serial drivers

 drivers/tty/serial/21285.c          |  2 +-
 drivers/tty/serial/8250/8250_mtk.c  |  2 +-
 drivers/tty/serial/8250/8250_omap.c |  2 +-
 drivers/tty/serial/8250/8250_port.c |  2 +-
 drivers/tty/serial/altera_uart.c    |  2 +-
 drivers/tty/serial/ar933x_uart.c    |  2 +-
 drivers/tty/serial/arc_uart.c       |  2 +-
 drivers/tty/serial/dz.c             |  2 +-
 drivers/tty/serial/imx.c            |  3 +-
 drivers/tty/serial/lantiq.c         |  2 +-
 drivers/tty/serial/lpc32xx_hs.c     |  2 +-
 drivers/tty/serial/men_z135_uart.c  |  2 +-
 drivers/tty/serial/mps2-uart.c      |  2 +-
 drivers/tty/serial/msm_serial.c     |  2 +-
 drivers/tty/serial/mvebu-uart.c     |  2 +-
 drivers/tty/serial/owl-uart.c       |  2 +-
 drivers/tty/serial/pch_uart.c       |  2 +-
 drivers/tty/serial/pic32_uart.c     |  2 +-
 drivers/tty/serial/rda-uart.c       |  2 +-
 drivers/tty/serial/rp2.c            |  2 +-
 drivers/tty/serial/sccnxp.c         |  2 +-
 drivers/tty/serial/serial-tegra.c   |  2 +-
 drivers/tty/serial/serial_core.c    | 76 ++++++++++++++++++++++++++++-
 drivers/tty/serial/sprd_serial.c    |  2 +-
 drivers/tty/serial/timbuart.c       |  2 +-
 drivers/tty/serial/vt8500_serial.c  |  2 +-
 drivers/tty/serial/xilinx_uartps.c  |  2 +-
 include/linux/serial_core.h         |  2 +
 28 files changed, 103 insertions(+), 28 deletions(-)

-- 
2.20.1