linux-kernel - Re: [PATCH v1 04/10] serial: mps2-uart: add MPS2 UART driver

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Message-ID: <56700A45.3070109@arm.com>
Date:	Tue, 15 Dec 2015 12:40:37 +0000
From:	Vladimir Murzin <vladimir.murzin@....com>
To:	Andy Shevchenko <andy.shevchenko@...il.com>
CC:	Arnd Bergmann <arnd@...db.de>,
	Russell King <linux@....linux.org.uk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	Andreas Färber <afaerber@...e.de>,
	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	Mark Rutland <Mark.Rutland@....com>,
	Pawel Moll <Pawel.Moll@....com>,
	ijc+devicetree <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>, Jiri Slaby <jslaby@...e.cz>,
	Rob Herring <robh+dt@...nel.org>,
	devicetree <devicetree@...r.kernel.org>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
	"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
	linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 04/10] serial: mps2-uart: add MPS2 UART driver

On 12/12/15 23:39, Andy Shevchenko wrote:
> On Wed, Dec 2, 2015 at 11:33 AM, Vladimir Murzin
> <vladimir.murzin@....com> wrote:
>> This driver adds support to the UART controller found on ARM MPS2
>> platform.
> 
> Just few comments (have neither time not big desire to do full review).
> 

Still better than nothing ;) I'm mostly agree on points you had, so I've
just left some I'm doubt about...

>> +
>> +static void mps2_uart_enable_ms(struct uart_port *port)
>> +{
>> +}
>> +
>> +static void mps2_uart_break_ctl(struct uart_port *port, int ctl)
>> +{
>> +}
> 
> Are those required to be present? If not, remove them until you have
> alive code there.

A quick grep shows that core calls mps2_uart_break_ctl()
unconditionally, but, yes, it checks for presence of
mps2_uart_enable_ms() before jumping there, so it is safe to remove latter.

>> +static irqreturn_t mps2_uart_oerrirq(int irq, void *data)
>> +{
>> +       irqreturn_t handled = IRQ_NONE;
>> +       struct uart_port *port = data;
>> +       u8 irqflag = mps2_uart_read8(port, UARTn_INT);
>> +
>> +       spin_lock(&port->lock);
>> +
>> +       if (irqflag & UARTn_INT_RX_OVERRUN) {
>> +               struct tty_port *tport = &port->state->port;
>> +
>> +               mps2_uart_write8(port, UARTn_INT_RX_OVERRUN, UARTn_INT);
>> +               tty_insert_flip_char(tport, 0, TTY_OVERRUN);
>> +               port->icount.overrun++;
>> +               handled = IRQ_HANDLED;
>> +       }
>> +
>> +       /* XXX: this shouldn't happen? */
> 
> If shouldn't why it's there? Otherwise better to explain which
> conditions may lead to this.
> 

In practice I've never seen that happened and I think it never *should*
happen since we check if there is room in TX buffer. However, I could be
wrong here, so it is why that statement has question mark.

>> +       if (irqflag & UARTn_INT_TX_OVERRUN) {
>> +               mps2_uart_write8(port, UARTn_INT_TX_OVERRUN, UARTn_INT);
>> +               handled = IRQ_HANDLED;
>> +       }
>> +
>> +       spin_unlock(&port->lock);
>> +
>> +       return handled;
>> +}
>> +
...
>> +static void mps2_uart_release_port(struct uart_port *port)
>> +{
>> +}
>> +
>> +static int mps2_uart_request_port(struct uart_port *port)
>> +{
>> +       return 0;
>> +}
>> +
> 
> Same question about empty stubs.

Looks like they called unconditionally by the core.

>> +static int __init mps2_uart_init(void)
>> +{
>> +       int ret;
>> +
>> +       ret = uart_register_driver(&mps2_uart_driver);
>> +       if (ret)
>> +               return ret;
>> +
>> +       ret = platform_driver_register(&mps2_serial_driver);
>> +       if (ret)
>> +               uart_unregister_driver(&mps2_uart_driver);
>> +
>> +       pr_info("MPS2 UART driver initialized\n");
>> +
>> +       return ret;
>> +}
>> +module_init(mps2_uart_init);
>> +
>> +static void __exit mps2_uart_exit(void)
>> +{
>> +       platform_driver_unregister(&mps2_serial_driver);
>> +       uart_unregister_driver(&mps2_uart_driver);
>> +}
>> +module_exit(mps2_uart_exit);
> 
> module_platform_driver();
> And move uart_*register calls to probe/remove.
> 

With this move we'll get uart_*register for every device probed, no?

Thanks
Vladimir

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