Re: [PATCH V6 3/5] tty: serial: meson: Describes the calculation of the UART baud rate clock using a clock frame

[Yu Tu <yu.tu@amlogic.com>]

Hi Jerome,
     Thank you very much for your reply. At present, the problem of 
switching UART baud rate stuck has been solved. I'm ready to send the 
next edition. However, I still don't understand your suggestion and need 
to communicate with you.

On 2022/1/21 5:40, Jerome Brunet wrote:
> [ EXTERNAL EMAIL ]
> 
> 
> On Tue 18 Jan 2022 at 11:09, Yu Tu <yu.tu@amlogic.com> wrote:
> 
>> Using the common Clock code to describe the UART baud rate clock
>> makes it easier for the UART driver to be compatible with the
>> baud rate requirements of the UART IP on different meson chips.
>>
>> Signed-off-by: Yu Tu <yu.tu@amlogic.com>
>> ---
>>   drivers/tty/serial/meson_uart.c | 195 +++++++++++++++++++++++---------
>>   1 file changed, 142 insertions(+), 53 deletions(-)
>>
>> diff --git a/drivers/tty/serial/meson_uart.c b/drivers/tty/serial/meson_uart.c
>> index 7570958d010c..92fa91c825e6 100644
>> --- a/drivers/tty/serial/meson_uart.c
>> +++ b/drivers/tty/serial/meson_uart.c
>> @@ -6,6 +6,7 @@
>>    */
>>   
>>   #include <linux/clk.h>
>> +#include <linux/clk-provider.h>
>>   #include <linux/console.h>
>>   #include <linux/delay.h>
>>   #include <linux/init.h>
>> @@ -65,9 +66,7 @@
>>   #define AML_UART_RECV_IRQ(c)		((c) & 0xff)
>>   
>>   /* AML_UART_REG5 bits */
>> -#define AML_UART_BAUD_MASK		0x7fffff
>>   #define AML_UART_BAUD_USE		BIT(23)
>> -#define AML_UART_BAUD_XTAL		BIT(24)
>>   
>>   #define AML_UART_PORT_NUM		12
>>   #define AML_UART_PORT_OFFSET		6
>> @@ -76,6 +75,11 @@
>>   #define AML_UART_POLL_USEC		5
>>   #define AML_UART_TIMEOUT_USEC		10000
>>   
>> +struct meson_uart_data {
>> +	struct clk	*baud_clk;
>> +	bool		use_xtal_clk;
>> +};
>> +
>>   static struct uart_driver meson_uart_driver;
>>   
>>   static struct uart_port *meson_ports[AML_UART_PORT_NUM];
>> @@ -293,19 +297,17 @@ static int meson_uart_startup(struct uart_port *port)
>>   
>>   static void meson_uart_change_speed(struct uart_port *port, unsigned long baud)
>>   {
>> +	struct meson_uart_data *private_data = port->private_data;
>>   	u32 val;
>>   
>>   	while (!meson_uart_tx_empty(port))
>>   		cpu_relax();
>>   
>> -	if (port->uartclk == 24000000) {
>> -		val = ((port->uartclk / 3) / baud) - 1;
>> -		val |= AML_UART_BAUD_XTAL;
>> -	} else {
>> -		val = ((port->uartclk * 10 / (baud * 4) + 5) / 10) - 1;
>> -	}
>> +	val = readl(port->membase + AML_UART_REG5);
>>   	val |= AML_UART_BAUD_USE;
>>   	writel(val, port->membase + AML_UART_REG5);
>> +
>> +	clk_set_rate(private_data->baud_clk, baud);
>>   }
>>   
>>   static void meson_uart_set_termios(struct uart_port *port,
>> @@ -395,11 +397,20 @@ static int meson_uart_verify_port(struct uart_port *port,
>>   
>>   static void meson_uart_release_port(struct uart_port *port)
>>   {
>> -	/* nothing to do */
>> +	struct meson_uart_data *private_data = port->private_data;
>> +
>> +	clk_disable_unprepare(private_data->baud_clk);
>>   }
>>   
>>   static int meson_uart_request_port(struct uart_port *port)
>>   {
>> +	struct meson_uart_data *private_data = port->private_data;
>> +	int ret;
>> +
>> +	ret = clk_prepare_enable(private_data->baud_clk);
>> +	if (ret)
>> +		return ret;
>> +
>>   	return 0;
>>   }
>>   
>> @@ -629,57 +640,105 @@ static struct uart_driver meson_uart_driver = {
>>   	.cons		= MESON_SERIAL_CONSOLE,
>>   };
>>   
>> -static inline struct clk *meson_uart_probe_clock(struct device *dev,
>> -						 const char *id)
>> -{
>> -	struct clk *clk = NULL;
>> -	int ret;
>> -
>> -	clk = devm_clk_get(dev, id);
>> -	if (IS_ERR(clk))
>> -		return clk;
>> -
>> -	ret = clk_prepare_enable(clk);
>> -	if (ret) {
>> -		dev_err(dev, "couldn't enable clk\n");
>> -		return ERR_PTR(ret);
>> -	}
>> -
>> -	devm_add_action_or_reset(dev,
>> -			(void(*)(void *))clk_disable_unprepare,
>> -			clk);
>> -
>> -	return clk;
>> -}
>> +static struct clk_div_table xtal_div_table[] = {
>> +	{0, 3},
>> +	{1, 1},
>> +	{2, 2},
>> +	{3, 2},
>> +};
>>   
>> -static int meson_uart_probe_clocks(struct platform_device *pdev,
>> -				   struct uart_port *port)
>> +static int meson_uart_probe_clocks(struct uart_port *port)
>>   {
>> -	struct clk *clk_xtal = NULL;
>> -	struct clk *clk_pclk = NULL;
>> -	struct clk *clk_baud = NULL;
>> +	struct meson_uart_data *private_data = port->private_data;
>> +	struct clk *clk_baud, *clk_xtal;
>> +	struct clk_hw *hw;
>> +	char clk_name[32];
>> +	struct clk_parent_data use_xtal_mux_parents[2] = {
>> +		{ .index = -1, },
>> +		{ .index = -1, },
>> +	};
> 
> You are using hw pointers later, you don't need to init the index to -1
> I think
> 
I'm going to delete them in the next version.
like: struct clk_parent_data use_xtal_mux_parents[2] = { };
>>   
>> -	clk_pclk = meson_uart_probe_clock(&pdev->dev, "pclk");
>> -	if (IS_ERR(clk_pclk))
>> -		return PTR_ERR(clk_pclk);
>> +	clk_baud = devm_clk_get(port->dev, "baud");
>> +	if (IS_ERR(clk_baud)) {
>> +		dev_err(port->dev, "Failed to get the 'baud' clock\n");
>> +		return PTR_ERR(clk_baud);
>> +	}
>>   
>> -	clk_xtal = meson_uart_probe_clock(&pdev->dev, "xtal");
>> +	clk_xtal = devm_clk_get(port->dev, "xtal");
>>   	if (IS_ERR(clk_xtal))
>> -		return PTR_ERR(clk_xtal);
>> -
>> -	clk_baud = meson_uart_probe_clock(&pdev->dev, "baud");
>> -	if (IS_ERR(clk_baud))
>> -		return PTR_ERR(clk_baud);
>> +		return dev_err_probe(port->dev, PTR_ERR(clk_xtal),
>> +				     "Failed to get the 'xtal' clock\n");
>> +
>> +	if (private_data->use_xtal_clk) {
>> +		snprintf(clk_name, sizeof(clk_name), "%s#%s", dev_name(port->dev),
>> +			 "xtal_div");
>> +		hw = devm_clk_hw_register_divider_table(port->dev,
>> +							clk_name,
>> +							__clk_get_name(clk_baud),
>> +							CLK_SET_RATE_NO_REPARENT,
>> +							port->membase + AML_UART_REG5,
>> +							26, 2,
>> +							CLK_DIVIDER_READ_ONLY,
>> +							xtal_div_table, NULL);
>> +		if (IS_ERR(hw))
>> +			return PTR_ERR(hw);
>> +
>> +		use_xtal_mux_parents[1].hw = hw;
>> +	} else {
>> +		snprintf(clk_name, sizeof(clk_name), "%s#%s", dev_name(port->dev),
>> +			 "clk81_div4");
>> +		hw = devm_clk_hw_register_fixed_factor(port->dev,
>> +						       clk_name,
>> +						       __clk_get_name(clk_baud),
>> +						       CLK_SET_RATE_NO_REPARENT,
>> +						       1, 4);
>> +		if (IS_ERR(hw))
>> +			return PTR_ERR(hw);
>> +
>> +		use_xtal_mux_parents[0].hw = hw;
>> +	}
> 
> The above is still wrong.
> 
> use_xtal_mux_parents initialize both parent to nothing
> And you init the parent in the conditional above.
> It is means only one path is actually set instead of both.
> 
> The mux always has 2 sources - Both should be set regardless of the HW version
> You just add
> * /4 on path 0 on legacy SoC
> * the funky divider on path 1 on newer SoC.
> 
You do have a point, so I was wondering if you had any suggestions.
>>   
>> -	port->uartclk = clk_get_rate(clk_baud);
>> +	snprintf(clk_name, sizeof(clk_name), "%s#%s", dev_name(port->dev),
>> +		 "use_xtal");
>> +	hw = __devm_clk_hw_register_mux(port->dev, NULL,
>> +					clk_name,
>> +					ARRAY_SIZE(use_xtal_mux_parents),
>> +					NULL, NULL,
>> +					use_xtal_mux_parents,
>> +					CLK_SET_RATE_PARENT,
>> +					port->membase + AML_UART_REG5,
>> +					24, 0x1,
>> +					CLK_MUX_READ_ONLY,
>> +					NULL, NULL);
>> +	if (IS_ERR(hw))
>> +		return PTR_ERR(hw);
>> +
>> +	port->uartclk = clk_hw_get_rate(hw);
>> +
>> +	snprintf(clk_name, sizeof(clk_name), "%s#%s", dev_name(port->dev),
>> +		 "baud_div");
>> +	hw = devm_clk_hw_register_divider(port->dev,
>> +					  clk_name,
>> +					  clk_hw_get_name(hw),
>> +					  CLK_SET_RATE_PARENT,
>> +					  port->membase + AML_UART_REG5,
>> +					  0, 23,
>> +					  CLK_DIVIDER_ROUND_CLOSEST,
>> +					  NULL);
>> +	if (IS_ERR(hw))
>> +		return PTR_ERR(hw);
>> +
>> +	private_data->baud_clk = hw->clk;
>>   
>>   	return 0;
>>   }
>>   
>>   static int meson_uart_probe(struct platform_device *pdev)
>>   {
>> +	struct meson_uart_data *private_data;
>>   	struct resource *res_mem;
>>   	struct uart_port *port;
>> +	struct clk *pclk;
>>   	u32 fifosize = 64; /* Default is 64, 128 for EE UART_0 */
>>   	int ret = 0;
>>   	int irq;
>> @@ -705,6 +764,15 @@ static int meson_uart_probe(struct platform_device *pdev)
>>   	if (!res_mem)
>>   		return -ENODEV;
>>   
>> +	pclk = devm_clk_get(&pdev->dev, "pclk");
>> +	if (IS_ERR(pclk))
>> +		return dev_err_probe(&pdev->dev, PTR_ERR(pclk),
>> +				     "Failed to get the 'pclk' clock\n");
>> +
>> +	ret = clk_prepare_enable(pclk);
>> +	if (ret)
>> +		return ret;
>> +
> 
> I think this is unbalanced.
I don't understand what you mean. How should I change it? Can you tell 
me more specifically.
> 
>>   	irq = platform_get_irq(pdev, 0);
>>   	if (irq < 0)
>>   		return irq;
>> @@ -724,9 +792,13 @@ static int meson_uart_probe(struct platform_device *pdev)
>>   	if (IS_ERR(port->membase))
>>   		return PTR_ERR(port->membase);
>>   
>> -	ret = meson_uart_probe_clocks(pdev, port);
>> -	if (ret)
>> -		return ret;
>> +	private_data = devm_kzalloc(&pdev->dev, sizeof(*private_data),
>> +				    GFP_KERNEL);
>> +	if (!private_data)
>> +		return -ENOMEM;
>> +
>> +	if (device_get_match_data(&pdev->dev))
>> +		private_data->use_xtal_clk = true;
>>   
>>   	port->iotype = UPIO_MEM;
>>   	port->mapbase = res_mem->start;
>> @@ -740,6 +812,11 @@ static int meson_uart_probe(struct platform_device *pdev)
>>   	port->x_char = 0;
>>   	port->ops = &meson_uart_ops;
>>   	port->fifosize = fifosize;
>> +	port->private_data = private_data;
>> +
>> +	ret = meson_uart_probe_clocks(port);
>> +	if (ret)
>> +		return ret;
>>   
>>   	meson_ports[pdev->id] = port;
>>   	platform_set_drvdata(pdev, port);
>> @@ -766,10 +843,22 @@ static int meson_uart_remove(struct platform_device *pdev)
>>   }
>>   
>>   static const struct of_device_id meson_uart_dt_match[] = {
>> -	{ .compatible = "amlogic,meson6-uart" },
>> -	{ .compatible = "amlogic,meson8-uart" },
>> -	{ .compatible = "amlogic,meson8b-uart" },
>> -	{ .compatible = "amlogic,meson-gx-uart" },
>> +	{
>> +		.compatible = "amlogic,meson6-uart",
>> +		.data = (void *)false,
>> +	},
>> +	{
>> +		.compatible = "amlogic,meson8-uart",
>> +		.data = (void *)false,
>> +	},
>> +	{
>> +		.compatible = "amlogic,meson8b-uart",
>> +		.data = (void *)false,
>> +	},
>> +	{
>> +		.compatible = "amlogic,meson-gx-uart",
>> +		.data = (void *)true,
>> +	},
>>   	{ /* sentinel */ },
>>   };
>>   MODULE_DEVICE_TABLE(of, meson_uart_dt_match);
>