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

[zl020895]

Hi Andy,
Thanks for the Reviewed-by.

> Wondering if we should undo this in the port's .shutdown() callback.
I saw the shutdown path already covers it: dw8250_shutdown() calls
serial8250_do_shutdown(), which does
	up->ier = 0;
	serial_port_out(port, UART_IER, 0);
so both the IER shadow and hardware IER are cleared, including ETOI.

Best regards,
Long Zhao

At 2026-09-10 16:33:14, "Andy Shevchenko" <andriy.shevchenko@xxxxxxxxxxxxxxx> wrote:
>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@xxxxxxxxxxxxxxx>
>
>...
>
>> +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
>