Re: [PATCH] serial: meson: make the current driver compatible with S4

Re: [PATCH] serial: meson: make the current driver compatible with S4

[Neil Armstrong]

Hi,

On 06/12/2021 11:02, xianwei.zhao wrote:
> Because S4 UART use a different clock source, the baud rate calculation need to be updated.
> Reset the UART during initialization to clear previous status.
> 
> Signed-off-by: xianwei.zhao <xianwei.zhao@amlogic.com>
> ---
>  drivers/tty/serial/meson_uart.c | 50 +++++++++++++++++++++++++++------
>  1 file changed, 42 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/tty/serial/meson_uart.c b/drivers/tty/serial/meson_uart.c
> index efee3935917f..15a992ee6a28 100644
> --- a/drivers/tty/serial/meson_uart.c
> +++ b/drivers/tty/serial/meson_uart.c
> @@ -65,9 +65,11 @@
>  #define AML_UART_RECV_IRQ(c)		((c) & 0xff)
>  
>  /* AML_UART_REG5 bits */
> -#define AML_UART_BAUD_MASK		0x7fffff
> +#define AML_UART_BAUD_MASK		GENMASK(22, 0)
>  #define AML_UART_BAUD_USE		BIT(23)
>  #define AML_UART_BAUD_XTAL		BIT(24)
> +#define AML_UART_BAUD_XTAL_TICK		BIT(26)
> +#define AML_UART_BAUD_XTAL_DIV2		BIT(27)
>  
>  #define AML_UART_PORT_NUM		12
>  #define AML_UART_PORT_OFFSET		6
> @@ -80,6 +82,14 @@ static struct uart_driver meson_uart_driver;
>  
>  static struct uart_port *meson_ports[AML_UART_PORT_NUM];
>  
> +/*
> + * struct aml_uart - device data
> + * @xtal_tick_en: A clock source that calculates baud rates
> + */
> +struct aml_uart {

please change to a better name like meson_uart_data and pass it as data of meson_uart_dt_match

> +	unsigned int xtal_tick_en;
> +};
> +
>  static void meson_uart_set_mctrl(struct uart_port *port, unsigned int mctrl)
>  {
>  }
> @@ -103,7 +113,7 @@ static void meson_uart_stop_tx(struct uart_port *port)
>  	u32 val;
>  
>  	val = readl(port->membase + AML_UART_CONTROL);
> -	val &= ~AML_UART_TX_INT_EN;
> +	val &= ~AML_UART_TX_EN;

Seems to be a cosmetic change, please split this in a separate patch.

>  	writel(val, port->membase + AML_UART_CONTROL);
>  }
>  
> @@ -121,12 +131,12 @@ static void meson_uart_shutdown(struct uart_port *port)
>  	unsigned long flags;
>  	u32 val;
>  
> -	free_irq(port->irq, port);
> +	devm_free_irq(port->dev, port->irq, port);

Please split this in a separate patch

>  
>  	spin_lock_irqsave(&port->lock, flags);
>  
>  	val = readl(port->membase + AML_UART_CONTROL);
> -	val &= ~AML_UART_RX_EN;
> +	val &= ~(AML_UART_RX_EN | AML_UART_TX_EN);

Seems it fixes a bug, split in a separate patch.

>  	val &= ~(AML_UART_RX_INT_EN | AML_UART_TX_INT_EN);
>  	writel(val, port->membase + AML_UART_CONTROL);
>  
> @@ -270,6 +280,7 @@ static int meson_uart_startup(struct uart_port *port)
>  	u32 val;
>  	int ret = 0;
>  
> +	meson_uart_reset(port);

Same, split in a separate patch

>  	val = readl(port->membase + AML_UART_CONTROL);
>  	val |= AML_UART_CLEAR_ERR;
>  	writel(val, port->membase + AML_UART_CONTROL);
> @@ -285,24 +296,37 @@ static int meson_uart_startup(struct uart_port *port)
>  	val = (AML_UART_RECV_IRQ(1) | AML_UART_XMIT_IRQ(port->fifosize / 2));
>  	writel(val, port->membase + AML_UART_MISC);
>  
> -	ret = request_irq(port->irq, meson_uart_interrupt, 0,
> -			  port->name, port);
> +	ret = devm_request_irq(port->dev, port->irq, meson_uart_interrupt,
> +			       IRQF_SHARED, port->name, port);

Same, split in a separate patch

>  
>  	return ret;
>  }
>  
>  static void meson_uart_change_speed(struct uart_port *port, unsigned long baud)
>  {
> +	struct aml_uart *aml_uart_data = port->private_data;
>  	u32 val;
>  
>  	while (!meson_uart_tx_empty(port))
>  		cpu_relax();
>  
> +	val = readl_relaxed(port->membase + AML_UART_REG5);
> +	val &= ~AML_UART_BAUD_MASK;
> +
>  	if (port->uartclk == 24000000) {
> -		val = ((port->uartclk / 3) / baud) - 1;
> -		val |= AML_UART_BAUD_XTAL;
> +		if (aml_uart_data->xtal_tick_en) {
> +			val = (port->uartclk / 2 + baud / 2) / baud  - 1;
> +			val |= (AML_UART_BAUD_XTAL | AML_UART_BAUD_XTAL_DIV2);

This should be triggered by a value in match data with a new compatible.

> +		} else {
> +			val = ((port->uartclk / 3) + baud / 2) / baud  - 1;
> +			val &= (~(AML_UART_BAUD_XTAL_TICK |
> +				AML_UART_BAUD_XTAL_DIV2));
> +			val |= AML_UART_BAUD_XTAL;
> +		}
>  	} else {
>  		val = ((port->uartclk * 10 / (baud * 4) + 5) / 10) - 1;
> +		val &= (~(AML_UART_BAUD_XTAL | AML_UART_BAUD_XTAL_TICK |
> +			AML_UART_BAUD_XTAL_DIV2));
>  	}
>  	val |= AML_UART_BAUD_USE;
>  	writel(val, port->membase + AML_UART_REG5);
> @@ -715,6 +739,7 @@ static int meson_uart_probe(struct platform_device *pdev)
>  {
>  	struct resource *res_mem, *res_irq;
>  	struct uart_port *port;
> +	struct aml_uart *aml_uart_data;
>  	u32 fifosize = 64; /* Default is 64, 128 for EE UART_0 */
>  	int ret = 0;
>  
> @@ -754,6 +779,14 @@ static int meson_uart_probe(struct platform_device *pdev)
>  	if (!port)
>  		return -ENOMEM;
>  
> +	aml_uart_data = devm_kzalloc(&pdev->dev, sizeof(struct aml_uart),
> +				     GFP_KERNEL);
> +	if (!aml_uart_data)
> +		return -ENOMEM;
> +
> +	of_property_read_u32(pdev->dev.of_node, "xtal_tick_en",
> +			     &aml_uart_data->xtal_tick_en);

This property is not documented in the bindings, instead introduce
a new compatible for the S4 and pass the "aml_uart" as the meson_uart_dt_match
data pointer.

And don't forget to submit the bindings change in another separate patch.

> +
>  	/* Use legacy way until all platforms switch to new bindings */
>  	if (of_device_is_compatible(pdev->dev.of_node, "amlogic,meson-uart"))
>  		ret = meson_uart_probe_clocks_legacy(pdev, port);
> @@ -775,6 +808,7 @@ static int meson_uart_probe(struct platform_device *pdev)
>  	port->x_char = 0;
>  	port->ops = &meson_uart_ops;
>  	port->fifosize = fifosize;
> +	port->private_data = aml_uart_data;
>  
>  	meson_ports[pdev->id] = port;
>  	platform_set_drvdata(pdev, port);
> 
> base-commit: 3f19fed8d0daed6e0e04b130d203d4333b757901
> 

Thanks,
Neil

Re: [PATCH] serial: meson: make the current driver compatible with S4

[Martin Blumenstingl]

Hi,

On Mon, Dec 6, 2021 at 11:02 AM xianwei.zhao <xianwei.zhao@amlogic.com> wrote:
>
> Because S4 UART use a different clock source, the baud rate calculation need to be updated.
> Reset the UART during initialization to clear previous status.
Could you please explain why it is needed (is the divide-by-three
divider broken, does this patch decrease clock jitter, ...)?
Think of it like this: if I add another Amlogic board.dts tomorrow,
then how do I know when the "xtal_tick_en" property needs to be set?

I found that the public datasheet for the A311D SoC already mentions
AML_UART_BAUD_XTAL_TICK and AML_UART_BAUD_XTAL_DIV2 but so far UART is
working fine on that SoC even without this patch.

[...]
> +       val = readl_relaxed(port->membase + AML_UART_REG5);
The old logic worked like this:
- calculate the new register values
- write "val" to the register

The new logic uses many extra steps:
- read the existing register value
- mask off some bits in the "val" variable
- update some bits in the "val" variable based on the calculations below
- write "val" to the register

Is there any reason why we need to change this logic to set AML_UART_REG5?


Best regards,
Martin