linux-kernel - Re: [PATCH v3 05/11] serial: sc16is7xx: fix broken port 0 uart init

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Message-Id: <20230525111034.fc59852a7f91c752ed39499d@hugovil.com>
Date:   Thu, 25 May 2023 11:10:34 -0400
From:   Hugo Villeneuve <hugo@...ovil.com>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        conor+dt@...nel.org, Jiri Slaby <jirislaby@...nel.org>,
        jringle@...dpoint.com, tomasz.mon@...lingroup.com,
        l.perczak@...lintechnologies.com,
        linux-serial <linux-serial@...r.kernel.org>,
        devicetree@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        linux-gpio@...r.kernel.org,
        Hugo Villeneuve <hvilleneuve@...onoff.com>
Subject: Re: [PATCH v3 05/11] serial: sc16is7xx: fix broken port 0 uart init

On Thu, 25 May 2023 14:20:59 +0300 (EEST)
Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com> wrote:

> On Thu, 25 May 2023, Hugo Villeneuve wrote:
> 
> > From: Hugo Villeneuve <hvilleneuve@...onoff.com>
> > 
> > While experimenting with rs485 configuration on a SC16IS752 dual UART,
> 
> You can remove this intro, it's not necessary.

Fixed.

 
> > 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.
> 
> Just start with:
> 
> sc16is7xx_config_rs485() function is called only for ...
> 
> > 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).
> 
> The max310x driver sets port->membase to ~0 (all ones) to solve the same 
> problem.

Fixed.


> > By implementing the same change in our
> > driver, uart_configure_port() is now correctly executed.
> 
> our driver -> this driver

Fixed.

 
> This changelog was really well describing the problem! :-)
> 
> > Fixes: dfeae619d781 ("serial: sc16is7xx")
> > 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?
> 
> Yeah, some other solution should be devised. Maybe we should add another 
> .iotype for thse kind of devices. But I'm fine with this for this fix.
> After editing the changelog, feel free to add:
> 
> Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>

Added.

 
> > Also, many drivers use port->iobase as an index, is it the correct way
> > to use it?
> 
> "Many" for this and max310x? Besides that, uartlite.c has a comment which 
> says "mark port in use".

Ok, 
anyway with your approval I will remove these comments which will not part of the final commit message anyway.

Hugo.


> > 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 af7e66db54b4..8a2fc6f89d36 100644
> > --- a/drivers/tty/serial/sc16is7xx.c
> > +++ b/drivers/tty/serial/sc16is7xx.c
> > @@ -1443,6 +1443,7 @@ 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;
> >