On Thu, Jun 23, 2022 at 09:58:58AM +0900, Dominique Martinet wrote: > From: Lukas Wunner <lukas@xxxxxxxxx> > > Core part of commit 2dd8a74fddd21b95dcc60a2d3c9eaec993419d69 upstream: > the PL011 driver does not support RS485 in the 5.10 tree yet so drop > that bit. > > RTS polarity of rs485-enabled ports is currently initialized on uart > open via: > > tty_port_open() > tty_port_block_til_ready() > tty_port_raise_dtr_rts() # if (C_BAUD(tty)) > uart_dtr_rts() > uart_port_dtr_rts() > > There's at least three problems here: > > First, if no baud rate is set, RTS polarity is not initialized. > That's the right thing to do for rs232, but not for rs485, which > requires that RTS is deasserted unconditionally. > > Second, if the DeviceTree property "linux,rs485-enabled-at-boot-time" is > present, RTS should be deasserted as early as possible, i.e. on probe. > Otherwise it may remain asserted until first open. > > Third, even though RTS is deasserted on open and close, it may > subsequently be asserted by uart_throttle(), uart_unthrottle() or > uart_set_termios() because those functions aren't rs485-aware. > (Only uart_tiocmset() is.) > > To address these issues, move RTS initialization from uart_port_dtr_rts() > to uart_configure_port(). Prevent subsequent modification of RTS > polarity by moving the existing rs485 check from uart_tiocmget() to > uart_update_mctrl(). > > That way, RTS is initialized on probe and then remains unmodified unless > the uart transmits data. If rs485 is enabled at runtime (instead of at > boot) through a TIOCSRS485 ioctl(), RTS is initialized by the uart > driver's ->rs485_config() callback and then likewise remains unmodified. > > The PL011 driver initializes RTS on uart open and prevents subsequent > modification in its ->set_mctrl() callback. That code is obsoleted by > the present commit, so drop it. > > Cc: Jan Kiszka <jan.kiszka@xxxxxxxxxxx> > Cc: Su Bao Cheng <baocheng.su@xxxxxxxxxxx> > Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx> > Link: https://lore.kernel.org/r/2d2acaf3a69e89b7bf687c912022b11fd29dfa1e.1642909284.git.lukas@xxxxxxxxx > Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> > Cc: stable@xxxxxxxxxxxxxxx # 5.10 > Reported-by: Daisuke Mizobuchi <mizo@xxxxxxxxxxxxxxxxx> > Tested-by: Daisuke Mizobuchi <mizo@xxxxxxxxxxxxxxxxx> > Signed-off-by: Dominique Martinet <dominique.martinet@xxxxxxxxxxxxxxxxx> > --- > Notes: > - as said in commit message, I've dropped the PL011 part of the > original patch as it is orthogonal to this change. We need this > serial core fix for the imx serial tty driver. > > - I wasn't really sure what to do with tags in the commit message, > everything below the 'Cc: stable' tag apply to the backport: > Mizobuchi-san tested the backport on the 5.10 branch with the imx > driver. > > - I'm not quite sure how far back it is relevant, for imx I assume > rs485 is broken since 58362d5be352 ("serial: imx: implement handshaking > using gpios with the mctrl_gpio helper") (4.5), and we did have that > problem all the way back in our older 4.9 product tree... but core > support back then wasn't as extensive for RS485 so we have a different > imx specific workaround there. > > - I do not use 5.15 but either version of this patch apply cleanly > there; I'd assume it'd be more appropriate to get the original > 2dd8a74fddd21b cherry-picked in this case for 5.15. Now queued up, thanks. greg k-h
