Re: [PATCH v6 11/13] serial: 8250_dw: add Ambarella CV75 quirks

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Fri, Sep 04, 2026 at 02:38:18PM +0800, Long Zhao via B4 Relay wrote:

> The Ambarella CV75 UART is Ambarella IP, not a Synopsys DesignWare
> licensed block. At the register level it is close enough to DW APB UART
> that a full custom UART driver is unnecessary: reuse 8250_dw with a
> small platform quirk.
> 
> Quirks:
> - keep IER ETOI (bit 5) set for RX timeout behaviour
> - skip set_rate; baud clock is managed outside the UART block

Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

...

> +static int dw8250_ier_mask_startup(struct uart_port *p)
> +{
> +	struct dw8250_data *d = to_dw8250_data(p->private_data);
> +	struct uart_8250_port *up = up_to_u8250p(p);
> +	int ret;
> +
> +	ret = serial8250_do_startup(p);
> +	if (ret)
> +		return ret;
> +
> +	/*
> +	 * Ambarella keeps variant IER bits (e.g. ETOI) set for correct RX
> +	 * timeout behaviour. Force them into the 8250 IER shadow so later
> +	 * generic IER updates do not clear them.
> +	 */

Wondering if we should undo this in the port's .shutdown() callback.

> +	up->ier |= d->pdata->ier_mask;
> +	serial_port_out(p, UART_IER, up->ier);
> +
> +	return 0;
> +}

-- 
With Best Regards,
Andy Shevchenko