Re: [PATCH v4 4/5] serial: 8250_dw: configure the Allwinner H616 UART

[Andy Shevchenko]

On Tue, Oct 27, 2026 at 05:05:32PM -0600, 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 describe H616's fixed 256-byte FIFO depth in platform
> data. Use common Allwinner setup helpers to configure the transmit load
> and receive trigger table from that depth.
> 
> 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.
> 
> Build the threshold table during setup and use the shared 8250 conversion
> helper to select the nearest lower threshold for sysfs writes.
> 
> 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.

...

> +	unsigned int fifo_size;

This is should come from DT (based on the property or compatible),

...

>  	u8			no_int_count;
> +	u8			rxtrig_bytes[UART_FCR_R_TRIG_MAX_STATE];

Why do you need it here? Can it be provided via driver_data?

...

> +/* The trigger is the masked, unshifted FCR receive trigger field. */
> +static unsigned int dw8250_sunxi_rxtrig_bytes(struct uart_port *p, unsigned int trigger)
> +{
> +	switch (trigger) {
> +	case UART_FCR_TRIGGER_1:
> +		return 1;
> +	case UART_FCR_TRIGGER_4:
> +		return p->fifosize / 4;
> +	case UART_FCR_TRIGGER_8:
> +		return p->fifosize / 2;
> +	default:
> +		return p->fifosize - 2;
> +	}
> +}

You don't need this, just provide a set of numbers directly.

-- 
With Best Regards,
Andy Shevchenko