Re: [PATCH v3 3/4] serial: 8250_dw: configure the Allwinner H616 UART

[Jiri Slaby <jirislaby@kernel.org>]

On 24. 10. 26, 22:22, James Hilliard wrote:
> H616 has 256-byte transmit and receive FIFOs, but its optional DesignWare
> component parameter register reads as zero. Generic 16550 probing leaves
> the port using the 16-byte FIFO configuration and its trigger-level table.
> 
> Keep PORT_16550A and preserve the FIFO size read from firmware by
> uart_read_port_properties(). Use it for the transmit load and derive the
> receive thresholds from the documented 1-byte, quarter-full, half-full
> and FIFO-depth-minus-two mapping. On H616 these are 1, 64, 128 and 254
> bytes; the normal 16550A half-full FCR setting selects 128 bytes.
> 
> Serialize trigger changes with termios and hold a runtime PM reference
> while programming FCR, preserving the FIFO contents. Propagate runtime
> resume errors before changing either the FCR shadow or the hardware.
> 
> Advertise automatic flow control so CRTSCTS enables MCR.AFCE. The
> DesignWare termios path selects hardware CTS handling, so the capability
> must be present for the corresponding hardware control to be enabled.
> 
> Select the fixed configuration through the platform setup callback.
> H616 has debug-divisor and RS485 control registers at the offsets used to
> detect DesignWare hardware RS485 and fractional-divisor support. Avoid
> those probes and retain the BUSY-safe integer divisor hook and software
> RS485 handling.
> 
> Use the existing SKIP_SET_RATE quirk to keep the UART clock enabled during
> termios changes. Its clock is a gate on the shared APB2 source, rather than
> an independent baud-rate generator.
> 
> Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
> ---
>   drivers/tty/serial/8250/8250_dw.c | 75 +++++++++++++++++++++++++++++++++++++++
>   1 file changed, 75 insertions(+)
> 
> diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
> index 9c171c5775a6..557832254c37 100644
> --- a/drivers/tty/serial/8250/8250_dw.c
> +++ b/drivers/tty/serial/8250/8250_dw.c
> @@ -19,6 +19,7 @@
>   #include <linux/io.h>
>   #include <linux/lockdep.h>
>   #include <linux/module.h>
> +#include <linux/mutex.h>
>   #include <linux/platform_device.h>
>   #include <linux/pm_runtime.h>
>   #include <linux/property.h>
> @@ -648,6 +649,73 @@ static void dw8250_setup(struct uart_port *p)
>   	dw8250_setup_dma(p);
>   }
>   
> +static unsigned int dw8250_sunxi_rxtrig_bytes(struct uart_port *p, unsigned int trigger)
> +{
> +	switch (trigger) {
> +	case 0:
> +		return 1;
> +	case 1:
> +		return p->fifosize / 4;
> +	case 2:
> +		return p->fifosize / 2;
> +	default:
> +		return p->fifosize - 2;

These constants are counterintuitive. Can you pass the fcr masked, 
unshifted and do:
case UART_FCR_TRIGGER_1:
   ...
case UART_FCR_TRIGGER_4:
   ...
...
instead?

> +	}
> +}
> +
> +static int dw8250_sunxi_get_rxtrig(struct uart_port *p)
> +{
> +	struct uart_8250_port *up = up_to_u8250p(p);
> +
> +	guard(uart_port_lock_irqsave)(p);
> +
> +	return dw8250_sunxi_rxtrig_bytes(p, UART_FCR_R_TRIG_BITS(up->fcr));

Here:
up->fcr & UART_FCR_TRIGGER_MASK

thanks,
-- 
js
suse labs