linux-kernel - Re: [RFC PATCH] serial: sc16is7xx: fix broken port 0 uart init

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Date:   Thu, 25 May 2023 00:09:24 -0400
From:   Hugo Villeneuve <hugo@...ovil.com>
To:     Hugo Villeneuve <hugo@...ovil.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Hugo Villeneuve <hvilleneuve@...onoff.com>,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] serial: sc16is7xx: fix broken port 0 uart init

On Wed, 17 May 2023 15:44:07 -0400
Hugo Villeneuve <hugo@...ovil.com> wrote:

> From: Hugo Villeneuve <hvilleneuve@...onoff.com>
> 
> While experimenting with rs485 configuration on a SC16IS752 dual UART,
> I found that the sc16is7xx_config_rs485() function was called only for
> the second port (index 1, channel B), causing initialization problems
> for the first port.
> 
> For the sc16is7xx driver, port->membase and port->mapbase are not set,
> and their default values are 0. And we set port->iobase to the device
> index. This means that when the first device is registered using the
> uart_add_one_port() function, the following values will be in the port
> structure:
>     port->membase = 0
>     port->mapbase = 0
>     port->iobase  = 0
> 
> Therefore, the function uart_configure_port() in serial_core.c will
> exit early because of the following check:
> 	/*
> 	 * If there isn't a port here, don't do anything further.
> 	 */
> 	if (!port->iobase && !port->mapbase && !port->membase)
> 		return;
> 
> Typically, I2C and SPI drivers do not set port->membase and
> port->mapbase. But I found that the max310x driver sets
> port->membase to ~0 (all ones). By implementing the same change in our
> driver, uart_configure_port() is now correctly executed.
> 
> Signed-off-by: Hugo Villeneuve <hvilleneuve@...onoff.com>
> ---
> 
> I am not sure if this change is the best long-term solution to this
> problem, and maybe uart_configure_port() itself could be modified to
> take into account the fact that some devices have all three *base
> values set to zero?
> 
> Also, many drivers use port->iobase as an index, is it the correct way
> to use it?
> 
> For example, for our driver, there was
> commit 5da6b1c079e6 ("sc16is7xx: Set iobase to device index") with the
> following explanation:
>     "Set the .iobase value to the relative index within the device to allow
>     infering the order through sysfs."
> 
>  drivers/tty/serial/sc16is7xx.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
> index 1a3143331c1f..3e0e63498052 100644
> --- a/drivers/tty/serial/sc16is7xx.c
> +++ b/drivers/tty/serial/sc16is7xx.c
> @@ -1432,6 +1432,7 @@ static int sc16is7xx_probe(struct device *dev,
>  		s->p[i].port.fifosize	= SC16IS7XX_FIFO_SIZE;
>  		s->p[i].port.flags	= UPF_FIXED_TYPE | UPF_LOW_LATENCY;
>  		s->p[i].port.iobase	= i;
> +		s->p[i].port.membase	= (void __iomem *)~0;
>  		s->p[i].port.iotype	= UPIO_PORT;
>  		s->p[i].port.uartclk	= freq;
>  		s->p[i].port.rs485_config = sc16is7xx_config_rs485;
> -- 
> 2.30.2

This patch is now integrated in the following series:
https://lkml.org/lkml/2023/5/25/7