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Date:   Tue, 4 Jul 2023 19:00:12 +0300
From:   Dmitry Rokosov <ddrokosov@sberdevices.ru>
To:     <neil.armstrong@linaro.org>
CC:     <gregkh@linuxfoundation.org>, <robh+dt@kernel.org>,
        <krzysztof.kozlowski+dt@linaro.org>, <conor+dt@kernel.org>,
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        <khilman@baylibre.com>, <martin.blumenstingl@googlemail.com>,
        <kelvin.zhang@amlogic.com>, <xianwei.zhao@amlogic.com>,
        <kernel@sberdevices.ru>, <rockosov@gmail.com>,
        <linux-amlogic@lists.infradead.org>,
        <linux-serial@vger.kernel.org>, <devicetree@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v1 3/5] tty: serial: meson: apply ttyS devname instead of
 ttyAML for new SoCs
Message-ID: <20230704160012.yoaqgk4plpyd6v26@CAB-WSD-L081021>
References: <20230704135936.14697-1-ddrokosov@sberdevices.ru>
 <20230704135936.14697-4-ddrokosov@sberdevices.ru>
 <eb0dab5b-2fc7-728c-c6e0-43d2db422ed5@linaro.org>
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 <9fde3632-2419-d36b-9c54-337155bb482e@linaro.org>
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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