On Tue, Jan 07, 2020 at 12:52:03AM +0100, Ivan Sistik wrote: > AMBA PL011 do not have hardware support for RS485. This implementation is > for drive enable signal (DE), which switch direction of RS485 driver chip. > This signal si drived by RTS pin. Correct multiplexor settings have to be > provided to Device Tree. Usually it is 'ctsrts', which is used for enabling > of HW flow control, too. > > DE signal is switched by starting transmition from serial core and data > transfer is initiated by first hrtimer if there is delay before send > enabled. > > There is missing FIFO empty interrupt in PL011. It is replaced by second > hrtimer which is started if there are no more data in port transmit buffer. > Notice that port transmit buffer is not the same as HW TX FIFO. Time of > this timmer is set to char send time and it is running until fifo is empty. > This kind of implementation cause that there can be unwanted delay of one > timer tick before DE signal is switched. This is used to prevent data loss > during transmit. Second timer can start first if there is delay after send > enabled. > > Signed-off-by: Ivan Sistik <sistik@xxxxxxxxxxxxxx> > --- > arch/arm/configs/bcm2835_defconfig | 1 + > drivers/tty/serial/Kconfig | 12 + > drivers/tty/serial/amba-pl011.c | 470 ++++++++++++++++++++++++++++- > 3 files changed, 480 insertions(+), 3 deletions(-) > > diff --git a/arch/arm/configs/bcm2835_defconfig b/arch/arm/configs/bcm2835_defconfig > index e9bc88937b1e..514888681913 100644 > --- a/arch/arm/configs/bcm2835_defconfig > +++ b/arch/arm/configs/bcm2835_defconfig > @@ -78,6 +78,7 @@ CONFIG_SERIAL_8250_SHARE_IRQ=y > CONFIG_SERIAL_8250_BCM2835AUX=y > CONFIG_SERIAL_AMBA_PL011=y > CONFIG_SERIAL_AMBA_PL011_CONSOLE=y > +CONFIG_SERIAL_AMBA_PL011_SOFT_RS485=y > CONFIG_SERIAL_DEV_BUS=y > CONFIG_TTY_PRINTK=y > CONFIG_I2C_CHARDEV=y > diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig > index df8bd0c7b97d..3cecd8a75691 100644 > --- a/drivers/tty/serial/Kconfig > +++ b/drivers/tty/serial/Kconfig > @@ -73,6 +73,18 @@ config SERIAL_AMBA_PL011_CONSOLE > your boot loader (lilo or loadlin) about how to pass options to the > kernel at boot time.) > > +config SERIAL_AMBA_PL011_SOFT_RS485 > + bool "RS485 software direction switching for ARM AMBA PL011 serial" > + depends on SERIAL_AMBA_PL011=y Why "=y" here? Shouldn't this just read: depends on SERIAL_AMBA_PL011? > + select SERIAL_CORE Is this needed? SERIAL_AMBA_PL011 already selects this. thanks, greg k-h
