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SubjectRe: [PATCH] tty: serial: amba-pl011: added RS485 support
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@3ksolutions.sk>
> ---
> 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

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