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

[zl020895 <zl020895@163.com>]

Hi Ilpo,

Thanks for the review.

I'll drop the serial_port_out() here and only keep:
	up->ier |= d->pdata->ier_mask;
so ETOI stays in the shadow and serial8250_set_ier() programs the
hardware later.

Best regards,
Long Zhao

At 2026-09-10 16:44:35, "Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com> wrote:
>On Fri, 4 Sep 2026, Long Zhao via B4 Relay wrote:
>
>> From: Long Zhao <longzhao@ambarella.com>
>> 
>> 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
>> 
>> Signed-off-by: Long Zhao <longzhao@ambarella.com>
>> ---
>>  drivers/tty/serial/8250/8250_dw.c | 34 ++++++++++++++++++++++++++++++++++
>>  1 file changed, 34 insertions(+)
>> 
>> diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
>> index 5fba913f3301..b15de40d1e2a 100644
>> --- a/drivers/tty/serial/8250/8250_dw.c
>> +++ b/drivers/tty/serial/8250/8250_dw.c
>> @@ -43,6 +43,9 @@
>>  #define RZN1_UART_xDMACR_8_WORD_BURST	(2 << 1)
>>  #define RZN1_UART_xDMACR_BLK_SZ(x)	((x) << 3)
>>  
>> +/* Ambarella IER: receive timeout interrupt enable */
>> +#define AMBARELLA_UART_IER_ETOI		BIT(5)
>> +
>>  /* Quirks */
>>  #define DW_UART_QUIRK_OCTEON		BIT(0)
>>  #define DW_UART_QUIRK_ARMADA_38X	BIT(1)
>> @@ -60,6 +63,7 @@
>>  
>>  struct dw8250_platform_data {
>>  	u8 usr_reg;
>> +	u8 ier_mask;
>>  	u32 cpr_value;
>>  	unsigned int quirks;
>>  };
>> @@ -572,6 +576,27 @@ static void dw8250_prepare_rx_dma(struct uart_8250_port *p)
>>  	dw8250_writel_ext(up, RZN1_UART_RDMACR, val);
>>  }
>>  
>> +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.
>> +	 */
>> +	up->ier |= d->pdata->ier_mask;
>> +	serial_port_out(p, UART_IER, up->ier);
>
>serial8250_do_startup() seems to defer IER update on purpose. Is it fine 
>to override that behavior here?
>
>-- 
> i.
>
>> +	return 0;
>> +}
>> +
>>  static void dw8250_quirks(struct uart_port *p, struct dw8250_data *data)
>>  {
>>  	unsigned int quirks = data->pdata->quirks;
>> @@ -606,6 +631,8 @@ static void dw8250_quirks(struct uart_port *p, struct dw8250_data *data)
>>  		p->serial_in = dw8250_serial_in32;
>>  		data->uart_16550_compatible = true;
>>  	}
>> +	if (data->pdata->ier_mask)
>> +		p->startup = dw8250_ier_mask_startup;
>>  }
>>  
>>  static void dw8250_reset_control_assert(void *data)
>> @@ -879,6 +906,12 @@ static const struct dw8250_platform_data dw8250_intc10ee = {
>>  	.quirks = DW_UART_QUIRK_IER_KICK,
>>  };
>>  
>> +static const struct dw8250_platform_data dw8250_ambarella_cv75_data = {
>> +	.usr_reg = DW_UART_USR,
>> +	.ier_mask = AMBARELLA_UART_IER_ETOI,
>> +	.quirks = DW_UART_QUIRK_SKIP_SET_RATE,
>> +};
>> +
>>  static const struct dw8250_platform_data dw8250_ultrarisc_dp1000_data = {
>>  	.usr_reg = DW_UART_USR,
>>  	.cpr_value = FIELD_PREP_CONST(DW_UART_CPR_ABP_DATA_WIDTH, 2) |
>> @@ -889,6 +922,7 @@ static const struct dw8250_platform_data dw8250_ultrarisc_dp1000_data = {
>>  };
>>  
>>  static const struct of_device_id dw8250_of_match[] = {
>> +	{ .compatible = "ambarella,cv75-uart", .data = &dw8250_ambarella_cv75_data },
>>  	{ .compatible = "snps,dw-apb-uart", .data = &dw8250_dw_apb },
>>  	{ .compatible = "cavium,octeon-3860-uart", .data = &dw8250_octeon_3860_data },
>>  	{ .compatible = "marvell,armada-38x-uart", .data = &dw8250_armada_38x_data },
>> 
>>