linux-kernel - Re: [PATCH v1 3/5] tty: serial: meson: apply ttyS devname instead of ttyAML for new SoCs

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Date:   Tue, 4 Jul 2023 17:59:33 +0300
From:   Dmitry Rokosov <ddrokosov@...rdevices.ru>
To:     <neil.armstrong@...aro.org>
CC:     <gregkh@...uxfoundation.org>, <robh+dt@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <conor+dt@...nel.org>,
        <jbrunet@...libre.com>, <jirislaby@...nel.org>,
        <khilman@...libre.com>, <martin.blumenstingl@...glemail.com>,
        <kelvin.zhang@...ogic.com>, <xianwei.zhao@...ogic.com>,
        <kernel@...rdevices.ru>, <rockosov@...il.com>,
        <linux-amlogic@...ts.infradead.org>,
        <linux-serial@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v1 3/5] tty: serial: meson: apply ttyS devname instead of
 ttyAML for new SoCs

Hello Neil,

Thank you for quick feedback!

On Tue, Jul 04, 2023 at 04:42:39PM +0200, neil.armstrong@...aro.org wrote:
> On 04/07/2023 15:59, Dmitry Rokosov wrote:
> > It is worth noting that the devname ttyS is a widely recognized tty name
> > and is commonly used by many uart device drivers. Given the established
> > usage and compatibility concerns, it may not be feasible to change the
> > devname for older SoCs. However, for new definitions, it is acceptable
> > and even recommended to use a new devname to help ensure clarity and
> > avoid any potential conflicts on lower or upper software levels. In
> > addition, modify the meson_uart_dt match data for g12a, a1, and s4 to
> > their appropriate values to ensure proper devname values and
> > functionality.
> 
> I'm not confident about modifying a global struct from a probe,
> I think you should add a separate meson_uart_driver/meson_serial_console couple
> with ttyS instead of ttyAML, refer to the right uart_driver in meson_uart_data
> and in probe() register it and pass it to uart_add_one_port().

Could you provide some insight into why you believe this solution may
not be acceptable? It appears that the meson_uart_driver and
meson_serial_console are not labeled with __init, which means it stay in
memory forever.

To clarify, are you suggesting a solution that involves segregating the
meson_uart_driver and meson_serial_console objects for each scenario and
subsequently declaring pointers to both objects within the
meson_uart_data? I want to make sure that I have accurately grasped the
essence of your proposed approach.

> > 
> > For more information please refer to IRC discussion at [1].
> > 
> > Links:
> >      [1]: https://libera.irclog.whitequark.org/linux-amlogic/2023-07-03
> > 
> > Signed-off-by: Dmitry Rokosov <ddrokosov@...rdevices.ru>
> > ---
> >   drivers/tty/serial/meson_uart.c | 33 +++++++++++++++++++++++++++++++--
> >   1 file changed, 31 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/tty/serial/meson_uart.c b/drivers/tty/serial/meson_uart.c
> > index 87c0eb5f2dba..361f9326b527 100644
> > --- a/drivers/tty/serial/meson_uart.c
> > +++ b/drivers/tty/serial/meson_uart.c
> > @@ -82,6 +82,7 @@ static struct uart_driver meson_uart_driver;
> >   static struct uart_port *meson_ports[AML_UART_PORT_NUM];
> >   struct meson_uart_data {
> > +	const char *dev_name;
> >   	bool has_xtal_div2;
> >   };
> > @@ -683,6 +684,7 @@ static int meson_uart_probe_clocks(struct platform_device *pdev,
> >   static int meson_uart_probe(struct platform_device *pdev)
> >   {
> > +	const struct meson_uart_data *priv_data;
> >   	struct resource *res_mem;
> >   	struct uart_port *port;
> >   	u32 fifosize = 64; /* Default is 64, 128 for EE UART_0 */
> > @@ -729,6 +731,18 @@ static int meson_uart_probe(struct platform_device *pdev)
> >   	if (ret)
> >   		return ret;
> > +	priv_data = device_get_match_data(&pdev->dev);
> > +
> > +	if (priv_data) {
> > +		struct console *cons = meson_uart_driver.cons;
> > +
> > +		meson_uart_driver.dev_name = priv_data->dev_name;
> > +
> > +		if (cons)
> > +			strscpy(cons->name, priv_data->dev_name,
> > +				sizeof(cons->name));
> > +	}
> > +
> >   	if (!meson_uart_driver.state) {
> >   		ret = uart_register_driver(&meson_uart_driver);
> >   		if (ret)
> > @@ -748,7 +762,7 @@ static int meson_uart_probe(struct platform_device *pdev)
> >   	port->x_char = 0;
> >   	port->ops = &meson_uart_ops;
> >   	port->fifosize = fifosize;
> > -	port->private_data = (void *)device_get_match_data(&pdev->dev);
> > +	port->private_data = (void *)priv_data;
> >   	meson_ports[pdev->id] = port;
> >   	platform_set_drvdata(pdev, port);
> > @@ -780,6 +794,17 @@ static int meson_uart_remove(struct platform_device *pdev)
> >   }
> >   static struct meson_uart_data meson_g12a_uart_data = {
> > +	.dev_name = "ttyAML",
> > +	.has_xtal_div2 = true,
> > +};
> > +
> > +static struct meson_uart_data meson_a1_uart_data = {
> > +	.dev_name = "ttyS",
> > +	.has_xtal_div2 = false,
> > +};
> > +
> > +static struct meson_uart_data meson_s4_uart_data = {
> > +	.dev_name = "ttyS",
> >   	.has_xtal_div2 = true,
> >   };
> > @@ -794,7 +819,11 @@ static const struct of_device_id meson_uart_dt_match[] = {
> >   	},
> >   	{
> >   		.compatible = "amlogic,meson-s4-uart",
> > -		.data = (void *)&meson_g12a_uart_data,
> > +		.data = (void *)&meson_s4_uart_data,
> > +	},
> > +	{
> > +		.compatible = "amlogic,meson-a1-uart",
> > +		.data = (void *)&meson_a1_uart_data,
> >   	},
> >   	{ /* sentinel */ },
> >   };
> 

-- 
Thank you,
Dmitry