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

Dmitry Rokosov
2023-07-04T16:00:47Z

On Tue, Jul 04, 2023 at 05:29:57PM +0200, neil.armstrong@linaro.org wrote:
> Hi.
>
> On 04/07/2023 16:59, Dmitry Rokosov wrote:
> > Hello Neil,
> >
> > Thank you for quick feedback!
> >
> > On Tue, Jul 04, 2023 at 04:42:39PM +0200, neil.armstrong@linaro.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.
> Yes but nothing forbids registering a g12a and an a1 uart on the same system,
> but you modify the meson_uart_driver/meson_serial_console struct.
> This could cause some issues.
>
> In practice this will never happen, but since we don't control the DT passed
> to the system we must make sure we take in account any scenario.
>

Yep, agree, this will cause an issue.

> >
> > 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.
>
> Not both, only the appropriate one.
>
> So either we make sure ttyAML and ttyS at exclusive at runtime, in this case we can
> modify the global meson_uart_driver/meson_serial_console, or you add
> a second set of uart_driver/console structs to handle this improbable case.

Got it, thank you for explanation! I will prepare the v2.

> >
> > > >
> > > > 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@sberdevices.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